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00:00:00There's a moment in Earth's history that feels like it was ripped from a science fiction movie,
00:00:05except it wasn't fiction.
00:00:07It happened, and it transformed our planet into an alien world that would terrify us today.
00:00:13Imagine breathing air so thick with oxygen that it would make you dizzy within minutes.
00:00:19A world where a single lightning strike could set even damp forests ablaze in unstoppable infernos.
00:00:26A realm where insects grew to monstrous proportions,
00:00:31with dragonflies sporting wingspans wider than your arm and millipedes longer than your sofa.
00:00:38Welcome to Earth during the Carboniferous Period,
00:00:42when our atmosphere contained 35% oxygen, nearly double what we breathe today,
00:00:48and for a staggering 60 million years this hypercharged atmosphere transformed life in ways that seem impossible.
00:00:56So, if these stories help you relax or whatever, hit like or subscribe.
00:01:02Also curious where everyone's at.
00:01:04Comment your city and time, reading through last video's comments and seeing Miami, Manchester and Melbourne all in there.
00:01:12The internet's weird, right?
00:01:15This isn't just a story about big bugs.
00:01:18It's about a bizarre chapter in our planet's biography,
00:01:21when the very chemistry of the air reshaped everything alive.
00:01:26It's about how our planet once created conditions that will never, can never, exist again.
00:01:33And it all began with an evolutionary accident.
00:01:36To step into the late Carboniferous world of 300 million years ago is to enter a planet in transformation.
00:01:43The continents weren't scattered as they are today.
00:01:47They were assembling into one massive supercontinent called Pangaea,
00:01:51a vast landmass stretching from pole to pole surrounded by a single global ocean.
00:01:57The land was raw, newly conquered by life, and it pulsed with humidity.
00:02:03But what truly set this era apart wasn't the shape of the continents.
00:02:07It was the forests.
00:02:09The Carboniferous period saw the rise of Earth's first true rainforests,
00:02:14and they were unlike anything alive today.
00:02:17Towering over the landscape were giant lycopcids, ancient club mosses, growing up to 100 feet tall.
00:02:24That's a 10-storey building, and technically they weren't even trees as we understand them.
00:02:29These plants had hollow, water-filled stems and reproduced with spores, not seeds.
00:02:35Alongside them stood seed ferns, giant horsetails and tree-sized fungi that reached nearly 25 feet high.
00:02:45It was a time so old that even plants were primitive beings.
00:02:49No flowers, no fruits, no grasses.
00:02:52The world was still a few hundred million years away from the hum of bees or the shade of oaks.
00:02:58These early forests were a brand new concept.
00:03:03Damp, dense and dark.
00:03:05An endless tangle of ferns and shadow choked with vines and crawling with life.
00:03:12Beneath the canopy, the floor was alive with decay.
00:03:16The Carboniferous swamp forests became massive peat bogs,
00:03:20trapping dead plant matter under waterlogged soil.
00:03:24Over millions of years, this carbon-rich soup compressed into the coal seams we still dig up today.
00:03:30But this lush world wasn't just a paradise.
00:03:33The dense plant life released massive amounts of oxygen into the atmosphere through photosynthesis,
00:03:40far more than the planet had ever seen.
00:03:43Some estimates suggest the air reached up to 35% oxygen, compared to 21% today.
00:03:51That's enough to make a modern human dizzy with every breath or make a candle burn twice as fast.
00:03:57And this oxygen-rich world was perfect for one group, arthropods.
00:04:02Insects, spiders, millipedes and scorpions flourished here, not just in numbers, but in scale.
00:04:12Vertebrates, by contrast, were still figuring things out.
00:04:16Early amphibians had made the leap onto land and some had grown large, six feet or more,
00:04:22but they were limited by moist skin and water-bound eggs.
00:04:27Reptiles were just beginning to emerge, developing the dry, scaly armour and shelled eggs that would one day give rise to dinosaurs.
00:04:37But for now, all of them were background players.
00:04:41It was a world of giants in Chitin.
00:04:44So, how did insects grow to such monstrous sizes?
00:04:49The secret lies in how they breathe.
00:04:52If you've ever wondered, insects rely on a completely different oxygen delivery system than mammals or reptiles,
00:04:59one that's elegant but critically inefficient.
00:05:03Insects don't have lungs.
00:05:05No diaphragm, no air sacs, no deep breaths.
00:05:09Instead, their entire respiratory system is a branching network of tiny tubes called trachea
00:05:16that deliver oxygen directly to their cells by passive diffusion.
00:05:21It's like having millions of microscopic snorkels running throughout their bodies.
00:05:26Oxygen simply drifts in through openings in their exoskeleton called spiracles and diffuses to where it's needed.
00:05:34This system works beautifully for small creatures, but there's a major problem.
00:05:40It doesn't scale well.
00:05:42The bigger the body, the harder it is to push oxygen all the way through without active transport.
00:05:48In today's atmosphere, this puts a hard cap on insect size, with the largest being the giant weeter in New Zealand.
00:05:56These chunky cricket relatives can reach up to 7 centimetres and weigh about 70 grams.
00:06:03Impressive, but still small enough to fit in your hand.
00:06:07But during the Carboniferous, the higher atmospheric oxygen concentration
00:06:12meant that even large-bodied insects could get enough oxygen passively.
00:06:17Suddenly, insects had plenty of room to grow.
00:06:20Atmospheric oxygen acted like an evolutionary steroid for invertebrates.
00:06:25This link isn't just theoretical.
00:06:28It's been tested.
00:06:30In 2007, researchers at Arizona State University raised modern insects in controlled environments
00:06:37with varying oxygen concentrations.
00:06:41The results were striking.
00:06:42When reared in hyperoxic conditions, some species of dragonflies and beetles grew significantly larger
00:06:51than their normal counterparts.
00:06:53The same principles that shaped giants millions of years ago still lurk inside their genomes today.
00:07:02Let's imagine standing in the middle of a Carboniferous jungle.
00:07:06Your boots sink slightly into the spongy ground.
00:07:09Dense, waterlogged peat formed from millions of years of decaying plant matter.
00:07:15The air is thick, not just with moisture, but with oxygen.
00:07:19All 35% of it.
00:07:21That's more than one and a half times what we breathe today.
00:07:26You feel light-headed.
00:07:27Your chest rises faster than usual.
00:07:29Not out of panic, but chemistry.
00:07:31That kind of oxygen density would make you dizzy, euphoric even, and dangerously flammable.
00:07:37One spark, one lightning strike, and even the wettest wood could go up in flames.
00:07:43Ever heard of spontaneous combustion?
00:07:46In this atmosphere, it wouldn't be a myth.
00:07:49You look down and see roots winding across the swamp floor like veins under the skin of the earth.
00:07:56Everywhere there's movement, tiny arthropods, early amphibians, things with too many legs and too little regard for your presence.
00:08:05But the real spectacle is above.
00:08:08You lift your gaze, and for a second your brain struggles to make sense of what it's seeing.
00:08:14Because up there in the canopy-shrouded sky are creatures that shouldn't exist.
00:08:19Not in your world.
00:08:21Not by your rules.
00:08:23You hear a flutter overhead.
00:08:25A pair of wings passes through the filtered light of the Carboniferous canopy.
00:08:30And for a moment, it looks like a bird, if birds had never been invented and evolution had tried something different.
00:08:39It's no bird.
00:08:40It's Palaeodictioptera.
00:08:42With wingspans ranging from 15 to 22 inches, these were some of the largest winged insects to ever exist.
00:08:50Fossils show they were among the earliest flyers in Earth's history, predating both true dragonflies and modern butterflies by tens of millions of years.
00:09:02But despite their size, they weren't predators.
00:09:05They were gentle gliders, relics of evolutionary experimentation.
00:09:11The name Palaeodictioptera means ancient net wing, and it fits.
00:09:17Their four main wings, two fore and two hind, were richly veined, forming geometric patterns like stained glass or spider silk.
00:09:27These insects also possessed a pair of additional small wing-like lobes near the front of their thorax, just behind the head.
00:09:35Often referred to as prothoracic winglets, that make six wing-like extensions in total, though only four were used for powered flight.
00:09:44These front lobes weren't true wings in the aerodynamic sense, but they may have served as stabilizers or represented an ancestral stage in wing evolution.
00:09:55Some paleontologists suggest these structures support the theory that insect wings evolved from gill-like structures in aquatic ancestors.
00:10:06Paleotic teopterans weren't designed for high-speed chases.
00:10:10They were herbivores, sippers of plant sap and feeders of soft tissues.
00:10:15Their mouthparts included a primitive proboscis, a needle-like projection used for piercing vegetation and extracting fluids.
00:10:23This made them among the earliest insects to evolve specialized feeding strategies beyond chewing, paving the way for everything from butterflies to mosquitoes.
00:10:34Some of them may have had vibrant patterns on their wings, like living kites suspended in sunlight, though we can only guess at their coloration.
00:10:43Fossils preserve the structure, not the paint, but their presence alone suggests something profound.
00:10:50Flight had arrived.
00:10:52For the first time in Earth's history, an animal wasn't limited to crawling or swimming.
00:10:57It could fly.
00:10:58Evolution had found a way to exploit a completely new realm on this planet.
00:11:04The air.
00:11:05Paleotic teoptera opened the skies to life.
00:11:08But they weren't the only ones taking advantage of the oxygen-rich atmosphere, and not all the aerial giants were peaceful plant sippers.
00:11:18Some were hunters, and they were about to change the game forever.
00:11:22Two wings, then four, wide, veined and beating like sails.
00:11:27Eyes the size of marbles.
00:11:30Legs like grappling hooks.
00:11:32And a wingspan nearly the length of your arm.
00:11:35This is Meganeura monyi, and for millions of years, it was the apex predator of the carboniferous skies.
00:11:45Reaching wingspans up to 28 inches and body lengths of 13 inches, Meganeura was a giant by any standard.
00:11:54Modern birds would struggle to match its silhouette, but Meganeura wasn't just big, it was lethal.
00:12:00Its four wings worked independently, allowing it to hover, bank, dive, and accelerate with surgical precision.
00:12:09Its eyes were enormous compound orbs, nearly 360 degrees of vision, like two full-dome cameras stitched into its skull, like modern dragonflies.
00:12:21It likely had a prey-capture success rate above 90%, and its prey wasn't gnats or mosquitoes.
00:12:28Fossil evidence and biomechanical modelling suggest it hunted other insects, juvenile amphibians, and possibly even small vertebrates.
00:12:39Its legs were barbed with long, claw-like tarsal segments that formed a spiny basket mid-flight.
00:12:47Anything caught in it, soft-bodied insects, smaller winged prey, was crushed mid-air.
00:12:53No ground kill, no chase needed, just strike and consume.
00:12:59Meganeura didn't glide awkwardly like a prehistoric experiment.
00:13:04It flew like it was born for it, and yet we still don't fully understand its life cycle.
00:13:11We assume it began, like modern dragonflies, as an aquatic nymph, likely a voracious predator in carboniferous ponds and marshes.
00:13:20Its juvenile form might have had gills, ambush strategies, and a taste for tadpoles or tiny crustaceans.
00:13:30Then, after molting, possibly several times, it would emerge, stretch its wings, and begin its rain above the canopy.
00:13:38Its fossil record is patchy but unmistakable.
00:13:42The first remains were discovered in 1880 in France, and additional specimens have since been found in Europe and North America.
00:13:50The wing venation, complex, grid-like, almost architectural, is a defining feature.
00:13:57It wasn't just strong, it was engineered.
00:13:59No other insect would come close to its aerial dominance until hundreds of millions of years later.
00:14:06While the skies of the Carboniferous were dominated by these dragonfly-like predators,
00:14:13the forest floor had its own terrors, and they were even more alien than what soared above.
00:14:19Creatures that would make your skin crawl not just because of their appearance,
00:14:24but because they represent one of our oldest, most primal fears.
00:14:28Something massive moves through the underbrush.
00:14:32Something with too many legs and an armoured body that shouldn't be possible at that size.
00:14:38You've just encountered one of the most nightmarish creations of the oxygen-rich world,
00:14:44a predator that would make even modern horror directors think twice about including it in their films.
00:14:50But what exactly was this creature, and how did it hunt in the primitive forests of the Carboniferous?
00:14:58The answer lies in one of the most remarkable fossil discoveries from this alien chapter of Earth's history.
00:15:06Meet Pulmonoscorpius kirktonensis, the largest scorpion to have ever walked the Earth.
00:15:13It stretched nearly 28 inches long from claw to stinger.
00:15:18That's about the size of a modern housecat, but with a completely different energy.
00:15:22Its body was covered in thick, kitiness armour, sculpted like interlocking plates of obsidian.
00:15:30Each movement was deliberate, each footfall calculated.
00:15:34This wasn't a creature in a hurry because it didn't need to be.
00:15:39Pulmonoscorpius was at the top of the food chain in its niche.
00:15:43An apex predator of the carboniferous forest floor.
00:15:47It hunted by ambush and by sensory precision, using a tool kit that seemed almost overbuilt for its time.
00:15:55Let's start with the pedipalps, those front appendages that look like arms ending in pincers.
00:16:01They were massive, muscle-packed weapons that could crush the exoskeletons of arthropods and pin-down struggling amphibians.
00:16:09Fossil morphology suggests they had serrated inner ridges, ideal for gripping slippery, soft-bodied prey.
00:16:17And of course, we need to talk about the tail.
00:16:21It arched high above its body, ending in a curved stinger, likely tipped with venom.
00:16:27While no direct fossil evidence of the venom gland survives, modern scorpions give us a clear analogue.
00:16:34And there's no reason to assume pulmonoscorpius was any less equipped.
00:16:39Its size alone would allow for significant venom volume, making even a single sting lethal to small vertebrates.
00:16:48Its eyes were another advantage.
00:16:51Pulmonoscorpius had two main types, a central pair that likely provided spatial depth perception and lateral eyes spread across its carapace for detecting motion and changes in light.
00:17:04Like modern arachnids, it may have also had sensory hairs called trichobothria, which could detect the slightest air movements.
00:17:13It could sense prey coming long before it arrived.
00:17:16Even vibrations on the ground caused by the soft steps of a juvenile tetrapod could be enough to give away its position.
00:17:26And that made pulmonoscorpius a perfect ambush predator.
00:17:30It didn't chase.
00:17:32It waited.
00:17:33It blended into the dark spaces beneath decaying club moss trunks or hunched beneath a blanket of fern litter where its armoured body was nearly indistinguishable from its surroundings.
00:17:46Then, snap, strike, inject, wait.
00:17:52It likely fed on a range of creatures.
00:17:56Smaller arthropods, mollusks, early amphibians, even the first primitive reptiles if they were slow or unlucky enough.
00:18:04Fossil records from Scotland's Kirkton Quarry place it squarely in the Carboniferous, thriving in what was once a wetland environment full of fallen vegetation and dense underbrush, perfect terrain for ambush predators.
00:18:19But despite its terrifying appearance, pulmonoscorpius was a one-time phenomenon.
00:18:26Modern scorpions rarely grow beyond eight inches, and even the largest living species, the emperor scorpion, is a fraction of its extinct ancestor.
00:18:37Still, for a brief moment in Earth's history, this ancient hunter was unchallenged.
00:18:42And yet, there were even bigger arthropods walking the Carboniferous landscape.
00:18:48At first, you might think it's a log being dragged across the forest floor, but then it bends around a tree trunk.
00:18:55This is Arthropleura, and it is quite literally the biggest land invertebrate that has ever lived.
00:19:01We know this not just from fossils, but from trackways.
00:19:06Massive, undulating impressions left in Carboniferous sediment and preserved in the stone record.
00:19:14Some are so wide and deep that you could lie inside them.
00:19:19Arthropleura measured up to eight and a half feet long and weighed as much as a large dog or more.
00:19:26It looked like a millipede, but was nothing like the ones that curl up in your garden.
00:19:30Arthropleura was a multi-ton centipede-tank hybrid covered in a hard, segmented exoskeleton,
00:19:38its dorsal plates locked together like roof tiles, giving it protection from above,
00:19:44while its dozens of leg pairs gave it traction through mud, root networks and decomposing plant matter.
00:19:52Despite its terrifying size, Arthropleura appears to have been a herbivore or detritivore,
00:19:59a decomposer feeding on decaying vegetation, mosses and perhaps even fungal matter.
00:20:06Fossil evidence from gut contents is sparse, but its jaw structure lacks the piercing or slicing features you'd expect from a predator.
00:20:16Instead, it likely ground up soft plant tissues, slowly converting the forest floor into mulch.
00:20:23And yet, in this world, being massive was a form of protection in itself.
00:20:30Size meant safety.
00:20:32Even predators like pulmonoscorpius would likely have thought twice before attacking an animal with a nearly impenetrable shell and mass on its side.
00:20:42No known vertebrate from that era could challenge it in a direct confrontation.
00:20:46Its widespread fossil evidence from Scotland, Germany and North America suggests it was common in carboniferous wetland forests,
00:20:56especially in areas prone to periodic flooding where decaying plant matter piled up fast.
00:21:03And yet, for all its size, we've never found its complete head.
00:21:07The exact structure of its mouthparts remains a mystery, as does much of its reproductive biology.
00:21:15Did it guard its eggs?
00:21:17Did it burrow?
00:21:18We can only speculate.
00:21:21And, as with so many giants of this era, what we know is impressive, but what we don't know is even more intriguing.
00:21:29The Carboniferous was a time of evolutionary experimentation, creatures testing the limits of what was physically possible in a hyperoxic world.
00:21:40Take Megarachne Cervonae, for example.
00:21:43For decades, that mega-prefix was taken literally.
00:21:47It was considered the largest spider to have ever lived.
00:21:51Paleontologists, journalists, even school textbooks described it as an eight-legged terror of the Carboniferous wetlands.
00:21:59With a leg span that would have covered a dinner plate.
00:22:02Until 2005, when a team led by Dr. Paul Seldon re-examined the original fossil, and what they found changed the narrative.
00:22:13Megarachne wasn't actually a spider.
00:22:16It wasn't even an arachnid.
00:22:18It belonged to a whole other family, the Eurypterids, a long-extinct group of arthropods more commonly known as sea scorpions.
00:22:27Megarachne didn't weave webs or creep through the underbrush.
00:22:31It crawled along the bottom of Carboniferous riverbeds, sweeping through the sediment with paddle-like limbs in search of food.
00:22:40It belonged to the same broad evolutionary family as scorpions, horseshoe crabs and trilobites,
00:22:46aquatic hunters and bottom feeders that thrived before fish and amphibians came to dominate the shallows.
00:22:54But even if it wasn't a spider, it was still huge.
00:22:57Estimates based on the fossil suggest a body length of about 21 inches,
00:23:02making it one of the largest known Eurypterids from freshwater environments.
00:23:06Its limbs were squat and broad, made for anchoring in soft mud and shoveling through detritus,
00:23:15and its feeding method was likely sweep-feeding,
00:23:18using specialized appendages to rake through silt and trap small prey like worms, insect larvae or crustaceans.
00:23:27Its thick carapace, preserved in beautiful detail in the fossil record,
00:23:33resembled the segmented body of a terrestrial spider,
00:23:37which is what originally confused researchers, but its structure was fundamentally different.
00:23:43No spinnerets, no fangs and no clear adaptations for air-breathing life.
00:23:48It lived in water, shallow, swampy, oxygen-rich water,
00:23:53where decaying vegetation fed a whole ecosystem of bottom dwellers and filter feeders.
00:23:59And Megarachne sat comfortably near the top of that aquatic world.
00:24:05It shared this lineage with giants.
00:24:07Its ancestors included Jaecolopterus renaniae and Pterygotus,
00:24:13marine Eurypterids that reached eight feet or more.
00:24:16Megarachne was smaller but unique,
00:24:19one of the few Eurypterids adapted to fresh water,
00:24:23bridging a critical transition from oceanic to terrestrial ecosystems.
00:24:28And when you look at its armoured body and flattened limbs,
00:24:32you see a different kind of terror,
00:24:34something so alien from us,
00:24:37so fundamentally different in its body plan,
00:24:40that it triggers an instinctive fear,
00:24:42a reaction to something that breaks all the rules of what an animal should be.
00:24:47But not all the terrors of the Carboniferous needed size or speed.
00:24:52Some just needed to be first.
00:24:56Trigonotarbids were among the first true terrestrial predators,
00:25:01land-based, air-breathing,
00:25:03and fully at home in the Carboniferous undergrowth.
00:25:05Some fossils date them to at least 419 million years ago,
00:25:11well before the Carboniferous.
00:25:13They were among the first creatures to abandon the safety of water
00:25:17and claim the land as their own.
00:25:20They look like spiders,
00:25:21and for decades they were often classified as such.
00:25:25Trigonotarbids were arachnids,
00:25:27yes, but not true spiders.
00:25:29They couldn't spin webs.
00:25:31They had no silk glands.
00:25:33Instead, their bodies were low,
00:25:35segmented,
00:25:36and heavily armoured with a shell-like carapace,
00:25:39protecting their head and thorax.
00:25:43Their abdomens were covered in plates,
00:25:46and their eight legs were spined and nimble,
00:25:49ideal for navigating a cluttered forest floor.
00:25:53Their prey were small, soft-bodied invertebrates.
00:25:57Their jaws, or chelicerae,
00:25:59were strong enough to crush and tear.
00:26:02Once captured,
00:26:03the prey was held in place by the legs
00:26:05and consumed alive.
00:26:07Some trigonotarbids were just a few millimetres long,
00:26:10and the largest about two inches.
00:26:13Their small size was their strength.
00:26:16In a world of enormous predators,
00:26:19they could go unnoticed.
00:26:21They breathed through book lungs,
00:26:24just like modern scorpions and spiders,
00:26:26and their internal anatomy shows a level of adaptation
00:26:30that's staggering for its time.
00:26:32Fossils from the Rhiney Chert site in Scotland
00:26:35preserve trigonotarbids in stunning detail,
00:26:39down to their respiratory organs,
00:26:40their mouthparts,
00:26:41even the hairs on their legs.
00:26:43And for tens of millions of years,
00:26:46they thrived.
00:26:47Then, quietly, they vanished.
00:26:49No catastrophic extinction event.
00:26:52No final predator to end their reign.
00:26:54They were simply outpaced by spiders,
00:26:57by scorpions,
00:26:59by more specialised arachnids who came later,
00:27:02and evolved the one thing trigonotarbids never did.
00:27:05Silk.
00:27:06But while trigonotarbids faded quietly into history,
00:27:11in the oceans and shallows,
00:27:13another kind of armour was evolving,
00:27:15one that didn't need webs or stealth
00:27:17because it had something else.
00:27:19Raw defence.
00:27:20This was Lepidocoleus,
00:27:24better known by its unofficial nickname,
00:27:26the Excalibur Worm,
00:27:28and despite being only a few millimetres long,
00:27:31it might have been the most heavily armoured animal
00:27:33in its size class in all of Earth's history.
00:27:37It lived over 400 million years ago,
00:27:40during the Devonian period,
00:27:42predating the Carboniferous rainforest
00:27:44by tens of millions of years.
00:27:47Its fossils were first uncovered
00:27:50in what is now Western Australia,
00:27:53in shallow reef environments
00:27:54that once bordered ancient seas.
00:27:57Lepidocoleus was protected
00:27:59by a full-body exoskeleton
00:28:01made of overlapping mineralised plates
00:28:05composed of crystalline calcite,
00:28:07a structure more like medieval chainmail
00:28:09than soft annelid tissue.
00:28:11These plates interlocked,
00:28:13forming a flexible yet nearly impenetrable suit of armour.
00:28:17They resembled miniature scales
00:28:19or overlapping shields,
00:28:21and when the worm curled into a ball,
00:28:24much like a pillbug,
00:28:25it presented only the outer plates to the world.
00:28:28No predator in that size class
00:28:30stood a chance of breaking through.
00:28:33That armour was so advanced
00:28:35it inspired its nickname,
00:28:37the Excalibur Worm,
00:28:39after the legendary sword of King Arthur,
00:28:41because like the blade in the stone,
00:28:44it seemed too perfect,
00:28:45too finely built,
00:28:47too out of place
00:28:48for such an ancient time.
00:28:50But like all evolutionary advantages,
00:28:53there was a trade-off.
00:28:55It may have been invulnerable to attack,
00:28:57but it paid the price in mobility.
00:28:59The armour slowed it down,
00:29:01limited its reach,
00:29:02and possibly made it harder
00:29:04to disperse to new habitats.
00:29:06It could defend,
00:29:07but it couldn't compete forever.
00:29:10We don't know exactly what it ate,
00:29:12possibly organic waste,
00:29:14microbial mats,
00:29:16or small detritus particles
00:29:18swept up from the seafloor.
00:29:20It didn't leave tooth marks.
00:29:22What it left was a fossilised marvel,
00:29:24a micro-scale masterpiece
00:29:26of evolutionary engineering.
00:29:28And then, quietly,
00:29:31it vanished.
00:29:33In a time of escalating predators
00:29:35and rising vertebrates,
00:29:37survival by defence alone
00:29:39was no longer enough.
00:29:41But for a time,
00:29:42deep in ancient tropical seas,
00:29:44this tiny creature lived
00:29:46wrapped in crystal plates,
00:29:48carried a fortress on its back,
00:29:50and dared the world to try.
00:29:52The key to understanding
00:29:54all these strange creatures
00:29:56lies in how they breathed.
00:29:58Arthropods have a unique
00:30:00respiratory system
00:30:01that worked remarkably well
00:30:02in the oxygen-rich
00:30:04carboniferous atmosphere,
00:30:05but imposed strict limits
00:30:07as oxygen levels declined.
00:30:10Modern insects have openings
00:30:12called spiracles
00:30:13along their bodies
00:30:15that connect to a network
00:30:16of increasingly tiny tubes
00:30:19called tracheae.
00:30:20These tubes branch throughout the body,
00:30:23delivering oxygen directly to tissues
00:30:25through passive diffusion.
00:30:27No pumping,
00:30:28no blood oxygen carriers
00:30:29like our haemoglobin.
00:30:31Oxygen simply moves
00:30:32from areas of high concentration
00:30:34to areas of low concentration.
00:30:37This system is incredibly efficient
00:30:40for small animals.
00:30:41Because oxygen goes straight
00:30:43to the cells that need it,
00:30:44insects can achieve
00:30:46extraordinarily high metabolic rates
00:30:48for their size,
00:30:49allowing for rapid wing beats
00:30:51and quick movements.
00:30:53But there's a critical limitation.
00:30:55Diffusion only works
00:30:57over short distances.
00:30:59The larger an insect grows,
00:31:01the longer its tracheal tubes
00:31:03must become,
00:31:04and the harder it is for oxygen
00:31:06to reach the center of the body.
00:31:09In today's atmosphere,
00:31:11with 21% oxygen,
00:31:13this creates a hard size limit.
00:31:15But in the Carboniferous,
00:31:17with 35% oxygen,
00:31:19that cap was lifted.
00:31:21Suddenly,
00:31:22passive diffusion could work
00:31:24over much greater distances.
00:31:26Giant insects weren't just possible,
00:31:29they were inevitable.
00:31:30The same physical principles
00:31:31that limit insect size today
00:31:34allowed them to grow enormous
00:31:35in the oxygen-rich past.
00:31:38But it wasn't just about breathing.
00:31:40The Carboniferous giants
00:31:42also had incredible strength.
00:31:44If you had to compare insects,
00:31:46mammals,
00:31:47and reptiles
00:31:48in a pound-for-pound strength contest,
00:31:51insects would easily win.
00:31:52The dung beetle can pull
00:31:541,141 times its body weight.
00:31:58If a human had to do the same,
00:32:01we'd need to be pulling
00:32:02six buses simultaneously.
00:32:04Other contenders include
00:32:06the Rhinoceros beetle
00:32:08with 850 times its body weight,
00:32:11the Leafcutter ant
00:32:12carrying 50 to 100 times its weight,
00:32:15and the Trapjaw ant
00:32:17with a bite force
00:32:18of 50 times its body weight.
00:32:20They outperform
00:32:21other powerhouses of nature
00:32:22like tigers,
00:32:24grizzly bears,
00:32:25and silverback gorillas.
00:32:26Even the mighty gorilla
00:32:28only manages about
00:32:2910 times its body weight.
00:32:32All of this comes
00:32:33from their exoskeleton structure
00:32:35and muscle arrangement,
00:32:36allowing them to exert
00:32:38tremendous force
00:32:39relative to their size.
00:32:41Now imagine
00:32:42these same mechanical advantages
00:32:44scaled up to the size of a dog
00:32:46or larger in the Carboniferous.
00:32:48The strength of these
00:32:49ancient arthropods
00:32:51would have been
00:32:51absolutely phenomenal.
00:32:54But the age of insects
00:32:55was nearing its end,
00:32:57and the cause
00:32:57wasn't what you might expect.
00:33:00No asteroid,
00:33:01no volcanic winter,
00:33:02no great extinction
00:33:04sweeping the board clean
00:33:06in a single geological breath.
00:33:08Instead,
00:33:09the end came
00:33:10like a long exhale,
00:33:11gradual,
00:33:12uneven,
00:33:13but final
00:33:14all the same.
00:33:15By the end
00:33:16of the Carboniferous,
00:33:17around 300 million years ago,
00:33:20the great swamplands
00:33:21that had dominated
00:33:22Earth's equatorial zones
00:33:24began to fracture,
00:33:25what was once
00:33:26a vast,
00:33:27humid jungle
00:33:28perfect for the massive
00:33:29oxygen-producing plants
00:33:31and the giants
00:33:32they supported
00:33:33started to break apart.
00:33:35Why?
00:33:36Because Pangea
00:33:37was closing in.
00:33:39The tectonic forces
00:33:40that were slowly assembling
00:33:42all the world's land masses
00:33:44into one enormous
00:33:45supercontinent
00:33:47did more than shift
00:33:48coastlines.
00:33:49They changed climate.
00:33:51As the continents collided,
00:33:53mountain ranges rose,
00:33:55altering air circulation
00:33:56and rainfall patterns.
00:33:59The moist,
00:33:59swampy habitats
00:34:00began to dry out,
00:34:01rainforests fragmented,
00:34:03peat bogs shrank.
00:34:05The carbon sink
00:34:06that had pumped
00:34:07Earth's atmosphere
00:34:08full of oxygen
00:34:09for millions of years
00:34:11was shutting down
00:34:12and the oxygen
00:34:13began to fall.
00:34:15From its peak,
00:34:16atmospheric oxygen levels
00:34:17started a slow,
00:34:19irreversible decline.
00:34:21By the early Permian period,
00:34:23they had dropped
00:34:23to something closer
00:34:24to 25%.
00:34:27Still high by modern standards,
00:34:29but not enough
00:34:29to sustain the physiology
00:34:31of giants.
00:34:32Large insects
00:34:33could no longer
00:34:34get enough oxygen
00:34:35to support their mass.
00:34:38And that wasn't
00:34:39the only problem.
00:34:40The collapse
00:34:41of the rainforest ecosystems
00:34:43triggered what scientists
00:34:44now call
00:34:45the Carboniferous
00:34:46Rainforest Collapse
00:34:48around 305 million years ago.
00:34:51As habitats dried
00:34:53and fragmented,
00:34:54many amphibians
00:34:55and large arthropods
00:34:57lost their ecological niches.
00:34:59Fire became more frequent
00:35:01in the drier climate.
00:35:03Fungi better suited
00:35:04to decomposition
00:35:05in cooler,
00:35:06oxygen-thin environments
00:35:08began to outcompete plants
00:35:10in breaking down wood,
00:35:11meaning less carbon
00:35:12was trapped in the soil
00:35:14and more stayed
00:35:15in the atmosphere
00:35:15as carbon dioxide.
00:35:17The biosphere
00:35:19was rebalancing itself,
00:35:21but not in favour
00:35:22of the giants.
00:35:24And then came
00:35:25the reptiles.
00:35:27With their amniotic eggs
00:35:28and scaly,
00:35:29watertight skin,
00:35:31early reptiles
00:35:32didn't need swamps.
00:35:33They could move inland,
00:35:35lay eggs on dry soil,
00:35:37breathe less oxygen,
00:35:38and keep growing.
00:35:39They weren't dominant yet,
00:35:41but they were flexible,
00:35:42adaptive,
00:35:43poised
00:35:44to inherit
00:35:44what the invertebrates
00:35:46could no longer hold.
00:35:48By the dawn
00:35:49of the Permian period,
00:35:50around 299 million years ago,
00:35:54the reign of the giant arthropods
00:35:56was effectively over.
00:35:58Some of their lineages survived.
00:36:00Smaller,
00:36:01more efficient,
00:36:02more conservative,
00:36:03but the age of giants
00:36:04had passed.
00:36:05It's tempting
00:36:06to imagine
00:36:07a different outcome.
00:36:08What if evolution
00:36:09had rolled the dice
00:36:10another way?
00:36:11Could insects
00:36:12have retained their size?
00:36:14Could we be living
00:36:14in a world
00:36:15with hummingbird-sized wasps
00:36:17and condor-sized beetles?
00:36:20Probably not,
00:36:21because once vertebrates
00:36:22got their act together,
00:36:24once lungs
00:36:25and complex circulatory systems
00:36:27entered the arms race,
00:36:29arthropods lost their edge.
00:36:31The vertebrate body plan
00:36:32allowed for more mobility,
00:36:34more adaptability,
00:36:35and most of all,
00:36:36scalability.
00:36:38And scale matters.
00:36:40When birds took to the skies
00:36:41and mammals emerged
00:36:43from the underbrush,
00:36:44the pressure was on.
00:36:45Competition intensified.
00:36:47New predators,
00:36:48new prey,
00:36:49new tactics.
00:36:50Insects didn't disappear,
00:36:52but they couldn't dominate
00:36:53the way they once did.
00:36:55Still,
00:36:56echoes of that
00:36:57ancient insect empire
00:36:59remain.
00:37:00We see it in the
00:37:01silent glide
00:37:02of dragonflies,
00:37:03whose flight mechanics
00:37:04haven't changed
00:37:05in 300 million years,
00:37:07in the segmented armor
00:37:09of millipedes,
00:37:10in the alien elegance
00:37:12of mantises
00:37:12patiently hunting
00:37:14like miniature dinosaurs.
00:37:16They're smaller now,
00:37:17less terrifying,
00:37:18but no less remarkable.
00:37:20They didn't evolve
00:37:21that much in the meantime.
00:37:23They scaled down,
00:37:25but many of the mechanisms
00:37:26we saw back then
00:37:27are still in place
00:37:29or with very few adaptations.
00:37:32But could such a
00:37:33hyperoxic world
00:37:34ever return?
00:37:36The answer is
00:37:36a definitive no
00:37:37and the reasons
00:37:38why reveal
00:37:39one of the most
00:37:40fascinating
00:37:41evolutionary arms races
00:37:43in Earth's history.
00:37:45The story centres
00:37:46around a seemingly
00:37:47mundane substance
00:37:48called lignin.
00:37:50Today,
00:37:50we take it for granted,
00:37:52but lignin
00:37:53was a revolutionary
00:37:54innovation
00:37:54when plants
00:37:55first evolved it
00:37:56roughly 400 million
00:37:58years ago.
00:37:59This complex polymer
00:38:01gave plants
00:38:02rigid support,
00:38:03allowing them to grow
00:38:04taller and compete
00:38:05for sunlight.
00:38:05Lignin is what
00:38:07puts the wood
00:38:08in woody plants.
00:38:09It's a key component
00:38:10of tree trunks,
00:38:11branches and other
00:38:12supportive tissues.
00:38:14But lignin had a property
00:38:16that would change
00:38:17Earth's atmosphere.
00:38:19It was extremely
00:38:20difficult to break down
00:38:21biologically.
00:38:22When the first plants
00:38:24evolved lignin,
00:38:25nothing on Earth
00:38:26could efficiently
00:38:27decompose it.
00:38:28When these plants
00:38:29died,
00:38:30instead of rotting
00:38:31completely,
00:38:32much of their
00:38:32carbon-rich tissue
00:38:34became buried
00:38:35in swampy conditions,
00:38:36eventually forming coal.
00:38:39This created
00:38:40a one-way flow
00:38:41of carbon
00:38:42from the atmosphere
00:38:43into plant tissue,
00:38:45then into the ground,
00:38:47and for every carbon atom
00:38:48locked away,
00:38:49free oxygen
00:38:50remained in the atmosphere.
00:38:52This imbalance,
00:38:53carbon going in
00:38:54without coming back out,
00:38:56drove oxygen levels
00:38:57higher and higher
00:38:58over millions of years.
00:39:00Then something happened
00:39:02that would forever
00:39:03change Earth's chemistry.
00:39:05Around the end
00:39:06of the Carboniferous period,
00:39:08a certain group
00:39:09of fungi evolved
00:39:10the ability
00:39:11to efficiently
00:39:12break down lignin.
00:39:13These white rot fungi
00:39:15developed enzymatic tools
00:39:17to dismantle
00:39:18the tough polymer,
00:39:19releasing its stored carbon
00:39:20back to the atmosphere.
00:39:22It was an evolutionary
00:39:24innovation as important
00:39:25as the evolution
00:39:26of lignin itself.
00:39:28Suddenly,
00:39:29the one-way carbon street
00:39:30became a two-way exchange.
00:39:33Dead plants
00:39:33could now be
00:39:34fully decomposed,
00:39:36their carbon returned
00:39:37to the atmosphere,
00:39:38preventing the build-up
00:39:39of oxygen.
00:39:41This fungal innovation
00:39:42was so efficient
00:39:43that it fundamentally
00:39:44rewired Earth's
00:39:46carbon cycle.
00:39:47Never again
00:39:48would conditions
00:39:49allow for the
00:39:50massive carbon burial
00:39:51that created
00:39:52the Carboniferous
00:39:53Oxygen Peak.
00:39:54The same early versions
00:39:56of these fungi
00:39:57can be found in amber
00:39:58from the late Carboniferous,
00:40:01right when oxygen levels
00:40:03began to fall.
00:40:05Today,
00:40:05every forest floor
00:40:07is teeming
00:40:07with lignin-degrading
00:40:09fungi.
00:40:10Every fallen log
00:40:11hosts a community
00:40:12of decomposers
00:40:14that can break it
00:40:15down completely.
00:40:16Modern trees
00:40:17still produce lignin,
00:40:18but now it's part
00:40:19of a balanced carbon cycle,
00:40:21rather than a one-way ticket
00:40:23to sequestration.
00:40:25The evolution
00:40:25of lignin-degrading
00:40:27fungi
00:40:27is why we'll never
00:40:29see 35% oxygen again.
00:40:32It's a perfect example
00:40:33of how life itself
00:40:35reshapes the planet's
00:40:36chemistry,
00:40:37creating feedback loops
00:40:38that persist
00:40:39for hundreds of
00:40:40millions of years.
00:40:42But fungi
00:40:43weren't the only
00:40:44organisms
00:40:45that changed the game.
00:40:46The evolution
00:40:47of termites
00:40:48around 150 million
00:40:50years ago
00:40:51introduced another
00:40:52highly efficient
00:40:53wood decomposing
00:40:54system.
00:40:55These insects,
00:40:56with their
00:40:57specialized gut
00:40:58microbiomes,
00:40:59became incredibly
00:41:00effective at breaking
00:41:01down cellulose
00:41:02and other plant
00:41:03materials.
00:41:04Today,
00:41:05termites process
00:41:06roughly a third
00:41:07of all dead wood
00:41:08in tropical environments.
00:41:10These decomposers,
00:41:12fungi,
00:41:13bacteria,
00:41:14termites,
00:41:15and others,
00:41:15now form a
00:41:16continuous
00:41:17clean-up crew
00:41:18that prevents
00:41:19the massive
00:41:19carbon burial
00:41:20that once drove
00:41:21oxygen levels
00:41:23so high.
00:41:24It's not just
00:41:24about the absence
00:41:25of swampy forests,
00:41:27it's about the
00:41:27presence of creatures
00:41:28that couldn't exist
00:41:30until evolution
00:41:32solved the
00:41:33lignin puzzle.
00:41:35This evolutionary
00:41:36arms race,
00:41:37plants developing
00:41:38tough lignin,
00:41:40fungi eventually
00:41:41developing ways
00:41:42to break it down,
00:41:43fundamentally changed
00:41:45Earth's atmosphere.
00:41:46It's a shift
00:41:47as significant
00:41:48as the great
00:41:49oxygenation event
00:41:50two billion years
00:41:51earlier,
00:41:52but in the
00:41:53opposite direction,
00:41:54not eliminating
00:41:55oxygen,
00:41:57but preventing it
00:41:58from reaching
00:41:59such extreme
00:42:00levels again.
00:42:02The Carboniferous
00:42:03Oxygen Peak
00:42:04wasn't just a
00:42:05strange chapter
00:42:06in Earth's history,
00:42:08it was a
00:42:08one-time event,
00:42:10a window of
00:42:10opportunity created
00:42:12by a temporary
00:42:13imbalance in the
00:42:14carbon cycle
00:42:15that life itself
00:42:16eventually corrected.
00:42:18And this brings us
00:42:19to another remarkable
00:42:21insight about our
00:42:22atmosphere.
00:42:23It isn't just a
00:42:24physical feature
00:42:25of the planet,
00:42:26it's a biological
00:42:27creation,
00:42:28shaped by the
00:42:29metabolic activities
00:42:30of countless
00:42:31organisms over
00:42:32billions of years.
00:42:34The air we breathe
00:42:35is, in a very real
00:42:37sense, a product
00:42:38of life itself.
00:42:39But the Carboniferous
00:42:41wasn't the only time
00:42:42oxygen levels
00:42:43changed dramatically.
00:42:45Let's zoom out
00:42:46to see the full
00:42:47sweep of oxygen's
00:42:48history on Earth,
00:42:49because it tells a
00:42:50story of revolution,
00:42:52balance, and the
00:42:53rise of complexity.
00:42:55For the first
00:42:56two billion years
00:42:57of Earth's existence,
00:42:59there was virtually
00:43:00no free oxygen
00:43:01in the atmosphere,
00:43:03less than
00:43:03one thousandth of
00:43:04one percent.
00:43:06Early life forms
00:43:07were anaerobes,
00:43:08using chemicals
00:43:09other than oxygen
00:43:10in their metabolism.
00:43:11The planet's
00:43:12atmosphere was
00:43:13dominated by
00:43:14nitrogen, carbon
00:43:16dioxide, and
00:43:18methane, more like
00:43:19today's Venus or
00:43:21Mars than
00:43:22modern Earth.
00:43:23Then, around
00:43:242.4 billion
00:43:26years ago,
00:43:27something
00:43:27revolutionary
00:43:28happened.
00:43:29Simple, single-celled
00:43:31organisms called
00:43:32cyanobacteria
00:43:33perfected
00:43:34photosynthesis,
00:43:36the ability to
00:43:36use sunlight to
00:43:37split water
00:43:38molecules, producing
00:43:39energy and
00:43:40releasing oxygen
00:43:41as a waste
00:43:42product.
00:43:43It was, from the
00:43:44bacteria's perspective,
00:43:45just a useful
00:43:46metabolic trick, but
00:43:48it would transform
00:43:49the planet.
00:43:51Slowly at first,
00:43:53then with gathering
00:43:53momentum, oxygen
00:43:55began to accumulate
00:43:56in the atmosphere.
00:43:57Much of it
00:43:58initially reacted with
00:43:59dissolved iron in
00:44:00the oceans, creating
00:44:02massive rust
00:44:03deposits called
00:44:04banded iron
00:44:05formations that we
00:44:06still mine today, but
00:44:08eventually the oxygen
00:44:09overwhelmed these
00:44:10chemical sinks and
00:44:12began to build up in
00:44:13the atmosphere.
00:44:14This event, the
00:44:15great oxygenation
00:44:17event, was Earth's
00:44:18first atmospheric
00:44:20revolution.
00:44:21Oxygen levels rose
00:44:22from nearly zero to
00:44:24perhaps one or two
00:44:25percent of the
00:44:26atmosphere.
00:44:27It was also Earth's
00:44:28first mass
00:44:29extinction, as
00:44:30anaerobic organisms
00:44:31that found oxygen
00:44:33toxic were wiped
00:44:34out or retreated to
00:44:35oxygen-free
00:44:36environments.
00:44:38For the next
00:44:39billion and a half
00:44:40years, oxygen
00:44:41levels remained
00:44:42relatively low,
00:44:44perhaps fluctuating
00:44:45between one and
00:44:46ten percent.
00:44:47Then, around
00:44:48eight hundred million
00:44:49years ago, another
00:44:51oxygen increase
00:44:52began, the
00:44:53neoproterozoic
00:44:54oxygenation event,
00:44:56pushing levels to
00:44:57perhaps 15 percent of
00:44:58the atmosphere.
00:44:59This may have helped
00:45:00trigger the evolution
00:45:01of the first complex
00:45:02animals.
00:45:04From about 550 to
00:45:06400 million years ago,
00:45:08oxygen gradually
00:45:09increased to around
00:45:1120 percent as the
00:45:12first land plants
00:45:13evolved and spread.
00:45:15Then came the
00:45:16dramatic rise during
00:45:17the Carboniferous that
00:45:19we've been exploring,
00:45:20reaching that peak of
00:45:2130 to 35 percent
00:45:23around 300 million
00:45:25years ago.
00:45:27Since then, oxygen
00:45:28has experienced
00:45:29several oscillations
00:45:31but never again
00:45:32reached such heights.
00:45:34There was a
00:45:34significant drop
00:45:35during the Permian
00:45:36and Triassic periods
00:45:38to perhaps 15 percent,
00:45:40followed by a rise
00:45:41during the Cretaceous
00:45:42period to around
00:45:4325 to 30 percent.
00:45:47For the past 60
00:45:47million years, levels
00:45:48have gradually
00:45:49declined to our
00:45:50current 21 percent.
00:45:53What's remarkable
00:45:54about this history is
00:45:55how closely it aligns
00:45:57with the evolution
00:45:58of complex life.
00:46:00Each major increase
00:46:01in atmospheric oxygen
00:46:02corresponds with the
00:46:04emergence of more
00:46:05complex, energy-demanding
00:46:07life forms.
00:46:08The great oxygenation
00:46:10event prepared Earth
00:46:11for the first
00:46:12eukaryotic cells.
00:46:14The neoproterozoic
00:46:16increase preceded the
00:46:17Cambrian explosion
00:46:19of animal diversity.
00:46:21The Carboniferous peak
00:46:22enabled the first
00:46:24largest large land animals.
00:46:26Oxygen isn't just
00:46:27a background condition
00:46:29for life.
00:46:30It's been a driver
00:46:31of evolutionary innovation,
00:46:33repeatedly enabling
00:46:34new forms of complexity.
00:46:37Higher oxygen levels
00:46:38allow for higher
00:46:39metabolic rates,
00:46:40which in turn support
00:46:42more complex body plans
00:46:43and behaviours.
00:46:45Today's atmosphere,
00:46:47with its 21 percent
00:46:48oxygen, represents
00:46:50a long-term equilibrium
00:46:52between oxygen-producing
00:46:54processes, primarily
00:46:55photosynthesis, and
00:46:57oxygen-consuming processes
00:46:59respiration, decomposition,
00:47:01and chemical weathering,
00:47:03it's high enough to support
00:47:04complex life like us,
00:47:07but low enough to prevent
00:47:08the runaway fires that would
00:47:10have been common in the
00:47:11Carboniferous.
00:47:13Human activities are causing
00:47:15a very slight decrease in
00:47:17atmospheric oxygen,
00:47:18about 0.001 percent per year,
00:47:22as we burn fossil fuels.
00:47:24This rate is too small
00:47:26to affect human health
00:47:27directly, but it represents
00:47:29yet another chapter in the
00:47:30long dance between life
00:47:32and its gaseous environment.
00:47:35The story of Earth's oxygen
00:47:36is a reminder that our planet
00:47:38is not static.
00:47:40It has gone through
00:47:41radical transformations,
00:47:43sometimes driven by
00:47:44the simplest life forms.
00:47:46The air we breathe today
00:47:48is the product of
00:47:49billions of years
00:47:50of biological activity,
00:47:52chemical reactions,
00:47:54and geological processes.
00:47:56It's a living atmosphere,
00:47:58constantly maintained
00:47:59by the biosphere.
00:48:01And it brings us back
00:48:03to the Carboniferous,
00:48:04a time when a temporary
00:48:06imbalance in this system
00:48:08created conditions so alien
00:48:10that they've never been
00:48:12repeated.
00:48:12The giant insects of that era
00:48:15were not just curiosities,
00:48:17they were the products
00:48:18of a specific atmospheric moment,
00:48:21beneficiaries of a brief window
00:48:23when oxygen reached levels
00:48:24that would never be seen again.
00:48:27Scientists have experimentally
00:48:29confirmed the connection
00:48:30between oxygen and insect size.
00:48:33In 2010,
00:48:35researchers at Arizona State University
00:48:38conducted an elegant experiment.
00:48:40they raised fruit flies
00:48:42in atmospheres with different
00:48:43oxygen concentrations
00:48:45over multiple generations.
00:48:48The results were clear.
00:48:49Higher oxygen led to
00:48:51larger body sizes,
00:48:52while lower oxygen
00:48:53produced smaller flies.
00:48:56Similar experiments
00:48:57with dragonflies showed
00:48:59that modern species
00:49:00raised in 35% oxygen
00:49:03developed larger wing-to-body
00:49:05ratios and grew to sizes
00:49:07well beyond their normal range.
00:49:10These studies demonstrate
00:49:11that the genetic potential
00:49:13for gigantism still exists
00:49:15in modern insects.
00:49:17They simply can't express
00:49:19these traits in today's atmosphere.
00:49:22But the story becomes
00:49:23even more interesting
00:49:24when we consider another factor,
00:49:27atmospheric density.
00:49:29The Carboniferous atmosphere
00:49:30wasn't just oxygen-rich,
00:49:32it was likely denser overall.
00:49:35Computer models suggest
00:49:36that the combination
00:49:37of higher oxygen
00:49:39and different carbon dioxide levels
00:49:41would have created air
00:49:43that was approximately
00:49:4420 to 25% denser
00:49:47than what we breathe today.
00:49:49For flying insects,
00:49:51this made an enormous difference.
00:49:54Denser air provides
00:49:55more lift for wings,
00:49:56making flight easier
00:49:58and less energetically expensive.
00:50:00Meganeura with its massive wingspan
00:50:03wasn't just able to breathe
00:50:04in the Carboniferous,
00:50:06it was able to fly
00:50:07more efficiently
00:50:08than would be possible today,
00:50:09even if modern oxygen levels
00:50:11could support its size.
00:50:13This density effect
00:50:15extended beyond insects.
00:50:17Early tetrapods,
00:50:19the amphibian-like creatures
00:50:20that were just beginning
00:50:22to exploit land environments,
00:50:24would have found
00:50:25the dense, oxygen-rich air
00:50:27much easier to breathe
00:50:29through their primitive lungs.
00:50:31It may have been
00:50:32a crucial factor
00:50:33allowing vertebrates
00:50:34to make the challenging transition
00:50:36from water to land.
00:50:39The Carboniferous atmosphere
00:50:40also had another distinctive feature.
00:50:43It was prone
00:50:44to spectacular,
00:50:46unstoppable fires.
00:50:48While modern forests
00:50:49can certainly burn
00:50:50under dry conditions,
00:50:52Carboniferous forests
00:50:53could burn
00:50:54even when wet.
00:50:56Laboratory experiments
00:50:57have shown that at 35% oxygen,
00:51:00even damp vegetation
00:51:02can sustain combustion.
00:51:04Ironically,
00:51:05these fires may have helped
00:51:07limit oxygen
00:51:08from climbing even higher.
00:51:10As oxygen increased,
00:51:11so did fire frequency,
00:51:13creating a negative feedback loop.
00:51:16More oxygen led to more fires,
00:51:18which consumed plant matter
00:51:19that would otherwise
00:51:20have been buried,
00:51:22returning carbon
00:51:23to the atmosphere
00:51:24and preventing further oxygen increase.
00:51:27Some scientists believe
00:51:29this fire feedback mechanism
00:51:31may have capped oxygen
00:51:32at around 35%,
00:51:34any higher,
00:51:35and fires would have been
00:51:37so frequent and intense
00:51:38that forests couldn't recover.
00:51:41Evidence for these ancient fires
00:51:43comes from charcoal deposits
00:51:45in Carboniferous sediments.
00:51:47These charcoal layers suggest
00:51:49regular, intense burning,
00:51:51another aspect of that alien world
00:51:54that's difficult to imagine today.
00:51:56The ripple effects
00:51:57of this hyperoxic world
00:51:59extended far beyond
00:52:01just creating giant insects.
00:52:05The entire ecosystem
00:52:06was shaped by these
00:52:08atmospheric conditions
00:52:09in ways that transformed
00:52:11the evolutionary trajectory
00:52:13of multiple lineages.
00:52:16Consider the forests themselves.
00:52:18The high oxygen levels
00:52:20allowed plants to grow taller
00:52:22and faster
00:52:23than would otherwise be possible.
00:52:25Carboniferous lycopcids
00:52:27like lepidodendron
00:52:28could reach maturity
00:52:30in just 10 to 15 years,
00:52:32astonishingly fast
00:52:34for a 100-foot tree.
00:52:36Modern redwoods,
00:52:37by comparison,
00:52:38take several centuries
00:52:39to reach their full height.
00:52:42This rapid growth
00:52:43was possible
00:52:44because high oxygen concentrations
00:52:46enhanced photosynthetic efficiency,
00:52:49plants could produce
00:52:51more energy
00:52:51with less effort,
00:52:53fuelling explosive growth.
00:52:55The Carboniferous forests
00:52:56weren't just bigger,
00:52:57they were more productive,
00:52:59generating biomass
00:53:00at rates
00:53:01that would be impossible today.
00:53:04These forests
00:53:05were also structurally different
00:53:07from modern ones.
00:53:08Without the selection pressure
00:53:10of efficient decomposers,
00:53:12Carboniferous plants
00:53:13didn't need to invest heavily
00:53:15in defensive compounds
00:53:16to deter herbivores
00:53:18and fungi.
00:53:19Their tissues
00:53:20contained fewer tannins,
00:53:22resins,
00:53:23and other compounds
00:53:24that make modern wood
00:53:25resistant to decay.
00:53:27This may have made them
00:53:28more vulnerable
00:53:29to the insects
00:53:30that fed on them,
00:53:31driving an arms race
00:53:32that contributed
00:53:33to the evolution
00:53:34of different feeding strategies.
00:53:37The high oxygen environment
00:53:39also affected reproduction.
00:53:41Many Carboniferous plants
00:53:43reproduced via spores
00:53:45rather than seeds,
00:53:47a more primitive method
00:53:48that requires water
00:53:49for fertilization.
00:53:51The humid,
00:53:52swampy conditions
00:53:53of the Carboniferous
00:53:54were perfect
00:53:55for this reproductive strategy,
00:53:57but as the climate
00:53:58dried toward the end
00:53:59of the period,
00:54:00plants with seeds,
00:54:02which can be fertilized
00:54:03with outstanding water,
00:54:05gained an evolutionary advantage.
00:54:08This transition
00:54:08from spore-based
00:54:10to seed-based reproduction
00:54:12was accelerated
00:54:13by the changing
00:54:14atmospheric conditions.
00:54:16For amphibians,
00:54:18the oxygen-rich air
00:54:19presented both opportunities
00:54:21and challenges.
00:54:22Early tetrapods
00:54:24like Eogyrinus
00:54:25and Proterogyrinus
00:54:27grew to impressive sizes.
00:54:29Some reached lengths
00:54:30of 15 feet or more.
00:54:32Their primitive lungs
00:54:33worked more efficiently
00:54:34in high oxygen conditions,
00:54:37allowing them to venture
00:54:38further from water
00:54:39than would otherwise
00:54:40be possible.
00:54:42But these amphibians
00:54:43still had a critical weakness.
00:54:46Their eggs had to be laid
00:54:47in water
00:54:48to prevent drying out.
00:54:49As the Carboniferous climate
00:54:51shifted
00:54:51and swampy habitats
00:54:53became less common,
00:54:54this limitation
00:54:55became increasingly problematic.
00:54:58This created
00:54:58an evolutionary pressure
00:55:00that would lead
00:55:00to one of the most
00:55:01important adaptations
00:55:02in vertebrate history,
00:55:04the amniotic egg.
00:55:06Around 320 million years ago,
00:55:09the first true reptiles evolved.
00:55:12Their key innovation
00:55:13was an egg
00:55:14with a protective shell
00:55:16and internal membranes
00:55:17that kept the embryo moist.
00:55:19This amniotic egg
00:55:20was a biological breakthrough,
00:55:23freeing vertebrates
00:55:24from their dependence
00:55:25on standing water
00:55:26for reproduction.
00:55:28Early reptiles
00:55:29like Hylonomus
00:55:30and Paleothyrus
00:55:31were small,
00:55:32perhaps 12 to 20 inches long,
00:55:34but they had a crucial advantage
00:55:36over their amphibian contemporaries.
00:55:40They could lay their eggs
00:55:41on land
00:55:41in relatively dry environments.
00:55:45This adaptation,
00:55:46combined with scaly skin
00:55:48that prevented water loss,
00:55:50allowed reptiles
00:55:51to thrive
00:55:51in the increasingly arid conditions
00:55:54of the late Carboniferous
00:55:55and early Permian.
00:55:57As oxygen levels fell,
00:55:59the advantage shifted
00:56:00toward organisms
00:56:01with more efficient
00:56:02respiratory systems.
00:56:03Reptiles,
00:56:05with their improved lungs
00:56:07and circulatory systems,
00:56:09were perfectly positioned
00:56:10to inherit the world
00:56:11that was becoming
00:56:12increasingly hostile
00:56:14to giant arthropods.
00:56:17The transition
00:56:17from the Carboniferous
00:56:19to the Permian period
00:56:20around 299 million years ago
00:56:24marked the end
00:56:25of the giant insect era
00:56:26and the beginning
00:56:27of the age of reptiles.
00:56:29Oxygen levels
00:56:30continued to drop,
00:56:32reaching perhaps
00:56:3315% during parts
00:56:35of the Permian,
00:56:36significantly lower
00:56:37than today's 21%.
00:56:39These changing
00:56:42atmospheric conditions
00:56:43drove one of the most
00:56:45significant transitions
00:56:47in Earth's history,
00:56:48from a world
00:56:49dominated by amphibians
00:56:51and giant arthropods
00:56:53to one increasingly
00:56:54controlled by reptiles.
00:56:56The descendants
00:56:57of those early reptiles
00:56:58would eventually
00:56:59include dinosaurs,
00:57:02pterosaurs,
00:57:03birds and mammals,
00:57:06including us.
00:57:08In a very real sense,
00:57:10we owe our existence
00:57:11to the falling oxygen levels
00:57:14that ended the reign
00:57:15of the arthropod giants.
00:57:18The Carboniferous oxygen peak
00:57:20wasn't just an interesting
00:57:22aberration,
00:57:23it was a pivotal moment
00:57:24in Earth's history
00:57:25that shaped the evolutionary
00:57:27trajectories of multiple lineages
00:57:29for hundreds of millions
00:57:31of years,
00:57:32and its effects
00:57:32continue to resonate today.
00:57:36Consider the coal
00:57:37that powers much
00:57:38of our modern world.
00:57:39Those black rocks
00:57:41that fuel power plants
00:57:42and industries
00:57:43are the compressed,
00:57:44transformed remains
00:57:46of Carboniferous forests.
00:57:48The name Carboniferous itself
00:57:50means coal-bearing,
00:57:52reflecting the abundance
00:57:53of coal deposits
00:57:54from this period.
00:57:55When we burn coal,
00:57:57we're releasing carbon
00:57:58that was sequestered
00:57:59over 300 million years ago,
00:58:02reversing the process
00:58:03that created the oxygen peak
00:58:05in the first place.
00:58:07Ironically,
00:58:08our use of fossil fuels
00:58:10is causing a very slight decrease
00:58:12in atmospheric oxygen,
00:58:14about 0.001% per year,
00:58:18This is too small
00:58:19to affect human health directly,
00:58:21but it represents
00:58:22a tiny step
00:58:23toward reversing
00:58:24the great oxygenation event
00:58:26that made complex life
00:58:28possible in the first place.
00:58:30Of course,
00:58:31at the current rate,
00:58:32it would take thousands of years
00:58:34to make a significant difference
00:58:36in oxygen levels,
00:58:37and other effects
00:58:38of fossil fuel use,
00:58:40particularly climate change,
00:58:42are far more immediate concerns.
00:58:45But the history
00:58:46of Earth's oxygen
00:58:47teaches us something profound
00:58:49about our planet.
00:58:50It is not a static stage
00:58:52upon which life performs.
00:58:54It is a dynamic system
00:58:56in which life and environment
00:58:57constantly shape each other.
00:58:59The oxygen we breathe
00:59:01is biologically generated,
00:59:03maintained,
00:59:04by the collective metabolism
00:59:05of countless organisms.
00:59:07Change the organisms,
00:59:09and you change the atmosphere.
00:59:12This perspective
00:59:12helps us understand
00:59:14why exoplanet researchers
00:59:16are so interested
00:59:17in detecting oxygen
00:59:18in the atmospheres
00:59:19of distant worlds.
00:59:21Free oxygen
00:59:22is relatively reactive
00:59:24and would quickly bind
00:59:25with other elements
00:59:26if not continuously replenished.
00:59:29On Earth,
00:59:29that replenishment
00:59:30comes from photosynthesis.
00:59:32Finding a similar oxygen signature
00:59:35on another planet
00:59:36would be a strong indicator
00:59:38of life,
00:59:39perhaps not intelligent life,
00:59:41but at least
00:59:41photosynthetic organisms
00:59:43altering their planetary atmosphere
00:59:45as they have on Earth.
00:59:47The search for biosignatures,
00:59:50chemical indications of life
00:59:51in exoplanet atmospheres,
00:59:53is one of the most exciting
00:59:55frontiers in astronomy,
00:59:57and it's informed
00:59:58by our understanding
00:59:59of how Earth's own atmosphere
01:00:01has been transformed
01:00:03by life
01:00:03over billions of years.
01:00:06But the oxygen story
01:00:07also has implications
01:00:09closer to home.
01:00:10Understanding how
01:00:11atmospheric composition
01:00:13affects evolution
01:00:14gives us insight
01:00:15into our own biology.
01:00:17Humans,
01:00:18like all mammals,
01:00:19are highly oxygen-dependent.
01:00:22Our high metabolic rates
01:00:23and energy-hungry brains
01:00:25require constant,
01:00:27efficient oxygen delivery.
01:00:29This is why we've evolved
01:00:32such sophisticated
01:00:33respiratory and circulatory systems,
01:00:36lungs with millions of alveoli
01:00:39to maximise gas exchange
01:00:41and haemoglobin-rich blood
01:00:43to transport oxygen
01:00:44throughout our bodies.
01:00:47These adaptations reflect
01:00:48our evolutionary history
01:00:50in an oxygen-rich environment.
01:00:52Unlike insects
01:00:54with their passive tracheal systems,
01:00:56vertebrates evolved active,
01:00:58pumping respiration
01:00:59that could scale up
01:01:00as animals grew larger,
01:01:02this allowed us
01:01:03to maintain
01:01:03high metabolic rates
01:01:05even as oxygen levels
01:01:07fluctuated
01:01:08over geological time.
01:01:11Our dependence on oxygen
01:01:12is so complete
01:01:14that even small changes
01:01:15in its availability
01:01:16have profound effects.
01:01:19Ascend to high altitude
01:01:20where oxygen partial pressure
01:01:22is lower
01:01:23and you'll quickly feel
01:01:24the effects,
01:01:25shortness of breath,
01:01:26fatigue,
01:01:27and potentially more serious conditions
01:01:29like altitude sickness.
01:01:31Stay at high altitude
01:01:33long enough
01:01:34and your body will adapt
01:01:35by producing
01:01:36more red blood cells
01:01:38to capture
01:01:38what oxygen is available,
01:01:40a physiological response
01:01:42that demonstrates
01:01:43how tightly our biology
01:01:44is linked to this gas.
01:01:46At the other extreme,
01:01:48hyperbaric oxygen therapy,
01:01:51exposure to higher
01:01:52than normal oxygen concentrations,
01:01:54is used medically
01:01:56to treat conditions
01:01:57like decompression sickness,
01:01:59carbon monoxide poisoning,
01:02:01and certain infections.
01:02:03The extra oxygen
01:02:04dissolves directly
01:02:05in the blood plasma,
01:02:07bypassing the normal
01:02:08hemoglobin transport system
01:02:10and delivering
01:02:11more of this vital gas
01:02:13to tissues that need it.
01:02:15But too much oxygen
01:02:17can be harmful.
01:02:18Hyperoxia,
01:02:19oxygen toxicity,
01:02:21can damage the lungs,
01:02:23central nervous system,
01:02:24and other tissues.
01:02:25Our cells have evolved
01:02:26to function
01:02:27within a relatively narrow range
01:02:29of oxygen concentrations.
01:02:32Like Goldilocks,
01:02:33we need it to be just right.
01:02:35Not too little,
01:02:36not too much.
01:02:39This biological balancing act
01:02:41reflects the long history
01:02:43of oxygen on Earth.
01:02:44Our physiology is adapted
01:02:46to the current
01:02:47atmospheric equilibrium.
01:02:4921% oxygen at sea level.
01:02:51Significant deviations
01:02:53in either direction
01:02:54would require
01:02:55substantial biological adjustments.
01:02:58If we were somehow
01:02:59transported back
01:03:01to the Carboniferous
01:03:02with its 35% oxygen,
01:03:04we'd experience something
01:03:06like oxygen intoxication.
01:03:08Our thinking would be impaired,
01:03:10our coordination would suffer,
01:03:12and eventually
01:03:13we might experience seizures.
01:03:16Evolution hasn't prepared us
01:03:17for such oxygen-rich conditions
01:03:19because they haven't existed
01:03:21for hundreds of millions of years.
01:03:24Conversely,
01:03:25if oxygen levels
01:03:26fell significantly,
01:03:28say,
01:03:28to the 15%
01:03:29that existed
01:03:30during parts of the Permian,
01:03:32we'd feel constantly
01:03:33out of breath
01:03:34like we were at high altitude.
01:03:36Our current physiology
01:03:38is calibrated
01:03:39to the atmosphere
01:03:39we've evolved in,
01:03:41not the atmospheres
01:03:42of the deep past.
01:03:44This raises
01:03:45an interesting question
01:03:46about human adaptability
01:03:48and space exploration.
01:03:49As we contemplate
01:03:51establishing human presence
01:03:53on other worlds,
01:03:54whether through visits
01:03:55or permanent settlements,
01:03:57we'll need to reckon
01:03:58with different atmospheric compositions.
01:04:00Mars,
01:04:02for example,
01:04:03has an atmosphere
01:04:04that's less than 1%
01:04:06the pressure of Earth's
01:04:07and contains
01:04:08only trace amounts
01:04:10of oxygen.
01:04:11Any human habitation
01:04:13would require
01:04:14artificially maintained environments
01:04:16with Earth-like air.
01:04:19Even more intriguing
01:04:20are proposals
01:04:21to terraform Mars
01:04:23to transform its atmosphere
01:04:25to make it more Earth-like.
01:04:27Such projects
01:04:28would need to consider
01:04:30not just temperature
01:04:31and pressure,
01:04:32but the specific gas mixture
01:04:34that human physiology requires.
01:04:36We are,
01:04:37in a very real sense,
01:04:39creatures of our atmosphere,
01:04:41shaped by its particular chemistry
01:04:43over millions of years
01:04:44of evolution.
01:04:46This brings us back
01:04:47to the Carboniferous
01:04:49and its lessons
01:04:49about atmospheric change.
01:04:52The transition
01:04:53from high to low oxygen
01:04:55at the end of that period
01:04:56drove massive evolutionary changes
01:04:59and extinction events.
01:05:00It's a reminder
01:05:01that when atmospheres change,
01:05:04life must adapt
01:05:05or perish.
01:05:07Today,
01:05:07we're causing
01:05:08atmospheric change
01:05:10of a different kind,
01:05:11not primarily
01:05:12in oxygen levels,
01:05:13but in greenhouse gases
01:05:15like carbon dioxide.
01:05:17The rate of this change
01:05:18is unprecedented
01:05:19in geological history,
01:05:21occurring over decades
01:05:22rather than millions of years.
01:05:24The lesson
01:05:25from the Carboniferous
01:05:27is clear.
01:05:28Atmospheric change
01:05:29drives biological change,
01:05:31often in ways
01:05:32that are difficult
01:05:33to predict.
01:05:34But there's another lesson
01:05:36from the Carboniferous
01:05:37that's equally important.
01:05:39The insects
01:05:39and other arthropods
01:05:41that once grew
01:05:42to enormous sizes
01:05:43didn't disappear
01:05:44when oxygen levels fell.
01:05:46They adapted.
01:05:47They evolved
01:05:48more efficient
01:05:49respiratory systems,
01:05:51reduced their body sizes
01:05:52to match the new
01:05:53atmospheric constraints
01:05:54and diversified
01:05:56into countless new niches.
01:05:58Today,
01:05:59insects are among
01:06:00the most successful
01:06:01animals on Earth,
01:06:03with over a million
01:06:04described species
01:06:05and many more
01:06:06yet to be discovered.
01:06:08They may be smaller
01:06:09than their Carboniferous
01:06:10ancestors,
01:06:11but they're arguably
01:06:12more successful.
01:06:13They've colonized
01:06:14virtually every terrestrial
01:06:16habitat on the planet,
01:06:18from deserts
01:06:19to rainforests,
01:06:20from mountain peaks
01:06:21to urban environments.
01:06:24This adaptability
01:06:25is a hallmark
01:06:26of life on Earth.
01:06:28When conditions change,
01:06:30life finds a way
01:06:31to continue,
01:06:32though often in new forms
01:06:34and with new dominant groups.
01:06:36The end of the Carboniferous
01:06:37oxygen peak
01:06:38didn't spell doom for life.
01:06:40It simply changed
01:06:42which organisms
01:06:43would thrive.
01:06:44As we face
01:06:45our own period
01:06:46of rapid environmental change,
01:06:49this perspective
01:06:49offers both caution
01:06:51and hope.
01:06:52The caution is that
01:06:53significant changes
01:06:54to Earth's atmosphere
01:06:55and climate
01:06:56will inevitably drive
01:06:58biological changes,
01:07:00including extinctions.
01:07:02The hope is that
01:07:02life as a whole
01:07:03has demonstrated
01:07:04remarkable resilience
01:07:06over billions of years,
01:07:08adapting to conditions
01:07:09far more extreme
01:07:10than anything humans
01:07:11have yet caused.
01:07:13Our own species
01:07:14with its tremendous
01:07:16technological capabilities
01:07:18has more adaptive options
01:07:20than any previous organism.
01:07:22We can create
01:07:23artificial environments,
01:07:24develop new technologies,
01:07:26and potentially
01:07:27even engineer
01:07:28biological adaptations,
01:07:30but we remain
01:07:31fundamentally dependent
01:07:32on the planetary systems
01:07:33that have sustained life
01:07:34for billions of years,
01:07:36the oxygen cycle
01:07:37among them.
01:07:38Understanding the history
01:07:40of Earth's atmosphere
01:07:41helps us appreciate
01:07:42how finely tuned
01:07:44our planet's chemistry
01:07:45is for life
01:07:46as we know it.
01:07:47The Carboniferous
01:07:48Oxygen Peak
01:07:49was a biological creation,
01:07:51the result of plants
01:07:53producing oxygen
01:07:54faster than it could
01:07:55be consumed.
01:07:57Its end was
01:07:58equally biological,
01:08:00the evolution
01:08:01of decomposers
01:08:02that could break down
01:08:03lignin
01:08:04and return carbon
01:08:05to the atmosphere.
01:08:07This balance,
01:08:08oxygen production
01:08:09versus consumption,
01:08:11continues today,
01:08:13maintained by the
01:08:14collective metabolism
01:08:15of the biosphere.
01:08:17It's a dynamic
01:08:17equilibrium,
01:08:19not a static condition,
01:08:20and it's one
01:08:21that can be disrupted
01:08:22by significant changes
01:08:24to the organisms
01:08:25that maintain it.
01:08:27The giants
01:08:28of the Carboniferous,
01:08:30the dragonflies
01:08:31with two-foot wingspans,
01:08:33the millipede-like
01:08:34arthropleura
01:08:35reaching eight feet
01:08:37in length,
01:08:38the cat-sized scorpions,
01:08:40were possible
01:08:40because of a specific
01:08:42atmospheric moment,
01:08:44a window of opportunity
01:08:45created by an imbalance
01:08:47in Earth's carbon cycle.
01:08:49When that imbalance
01:08:50was corrected
01:08:50by the evolution
01:08:51of lignin-degrading fungi,
01:08:53the window closed,
01:08:55never to reopen.
01:08:57But the impact
01:08:58of that brief
01:08:59hyperoxic world
01:09:00continues to reverberate
01:09:02through Earth's history.
01:09:03The coal formed
01:09:04during the Carboniferous fuels
01:09:06much of our modern civilization.
01:09:09The evolutionary pressures
01:09:10created by changing
01:09:12oxygen levels
01:09:13helped drive
01:09:14the development
01:09:14of the amniotic egg
01:09:16and the rise of reptiles.
01:09:19And the fossil record
01:09:20of giant arthropods
01:09:22provides a vivid demonstration
01:09:24of how atmospheric chemistry
01:09:26shapes the possibilities
01:09:27of life.
01:09:29The scientific investigation
01:09:30of carboniferous oxygen levels
01:09:33and giant arthropods
01:09:34continues today
01:09:36with new technologies
01:09:37providing unprecedented insights
01:09:40into this ancient world.
01:09:42One of the most exciting frontiers
01:09:44involves the study of amber,
01:09:46fossilized tree resin
01:09:47that sometimes contains
01:09:49tiny bubbles of ancient air.
01:09:51By analyzing these bubbles
01:09:53using advanced mass spectrometry,
01:09:56researchers can directly measure
01:09:58of the gas composition
01:09:59of ancient atmospheres.
01:10:01Recent studies
01:10:02of Cretaceous amber
01:10:04have confirmed
01:10:05elevated oxygen levels
01:10:07during that period,
01:10:08though not as high
01:10:09as the Carboniferous,
01:10:11lending support
01:10:12to the methods used
01:10:14to estimate
01:10:14even older
01:10:16atmospheric conditions.
01:10:18Another innovative approach
01:10:20involves examining
01:10:21the microscopic structure
01:10:23of plant fossils,
01:10:25the density of stomata,
01:10:26the small pores
01:10:28on leaf surfaces
01:10:29through which
01:10:30gas exchange occurs,
01:10:31is inversely related
01:10:33to carbon dioxide concentration.
01:10:36When CO2 is abundant,
01:10:37plants need fewer stomata.
01:10:39When it's scarce,
01:10:40they develop more.
01:10:41By counting stomatal density
01:10:43in fossil leaves,
01:10:44researchers can estimate
01:10:46ancient CO2 levels,
01:10:47which in turn helps
01:10:49constrain oxygen estimates.
01:10:52Advanced imaging techniques
01:10:53are also revolutionizing
01:10:55our understanding
01:10:56of arthropod respiration.
01:10:58CT scanning
01:10:59and synchrotron imaging
01:11:01allow scientists
01:11:02to visualize
01:11:03the internal anatomy
01:11:05of both fossil
01:11:06and modern insects
01:11:07in unprecedented detail.
01:11:10These studies
01:11:10have revealed
01:11:11that insects
01:11:12can actively control
01:11:13the diameter of their trachea,
01:11:15dilating them
01:11:16during periods
01:11:16of high oxygen demand
01:11:18like flight.
01:11:20This suggests
01:11:21that even Carboniferous
01:11:22giants had some ability
01:11:24to regulate
01:11:25their respiratory systems,
01:11:27though they remained
01:11:28fundamentally constrained
01:11:29by passive diffusion.
01:11:32Computer modeling
01:11:33has become another
01:11:34powerful tool.
01:11:36By creating detailed
01:11:37simulations
01:11:38of insect respiratory systems,
01:11:41researchers can test
01:11:42hypotheses
01:11:43about how size
01:11:44relates to oxygen requirements.
01:11:47These models suggest
01:11:48that in today's atmosphere,
01:11:49the theoretical maximum size
01:11:52for a flying insect
01:11:53is not much larger
01:11:54than the largest
01:11:55existing species.
01:11:57But in a 35% oxygen atmosphere,
01:12:00the size limit
01:12:01increases dramatically,
01:12:03aligning perfectly
01:12:05with the fossil evidence
01:12:06from the Carboniferous.
01:12:08The implications
01:12:09of this research
01:12:10extend beyond
01:12:12understanding Earth's past.
01:12:14As we explore
01:12:15other worlds,
01:12:16the question of how
01:12:17atmospheric composition
01:12:19affects the evolution
01:12:20of life
01:12:21becomes increasingly relevant.
01:12:23Mars once had
01:12:24a thicker atmosphere
01:12:25and liquid water
01:12:26on its surface.
01:12:28If life evolved there,
01:12:31how might it have been
01:12:32shaped by the Martian
01:12:33atmosphere's
01:12:34particular chemistry?
01:12:35What kinds of
01:12:37respiratory systems
01:12:38might evolve on worlds
01:12:40with different
01:12:41atmospheric compositions
01:12:42than Earth's?
01:12:44These questions
01:12:45aren't just academic.
01:12:47They inform our search
01:12:48for biosignatures,
01:12:50signs of life
01:12:51on other planets.
01:12:52By understanding
01:12:53how life and atmosphere
01:12:55interact on Earth,
01:12:56we develop better models
01:12:57for what to look for
01:12:59elsewhere.
01:13:00The Carboniferous Oxygen
01:13:02Peak also offers
01:13:03insights into potential
01:13:05futures for our own planet.
01:13:07While we'll never again
01:13:09see 35% oxygen
01:13:11due to the evolution
01:13:12of lignin-degrading organisms,
01:13:14human activities
01:13:16are causing
01:13:17other significant changes
01:13:18to atmospheric chemistry.
01:13:21The rapid increase
01:13:22in carbon dioxide
01:13:24from about 280 parts
01:13:26per million
01:13:27before the Industrial Revolution
01:13:29to over 420 parts
01:13:31per million today
01:13:33represents a rate of change
01:13:35unprecedented
01:13:35in geological history.
01:13:38Just as the shift
01:13:40from high to low oxygen
01:13:41drove major evolutionary changes
01:13:44at the end of the Carboniferous,
01:13:46today's atmospheric changes
01:13:48will likely drive
01:13:49biological adaptations.
01:13:51Some organisms will thrive
01:13:53in the new conditions,
01:13:55others will struggle.
01:13:56The specific winners and losers
01:13:58are difficult to predict,
01:13:59but the history of Earth's atmosphere
01:14:01suggests that significant change
01:14:04is inevitable.
01:14:04This perspective helps place
01:14:07current climate concerns
01:14:09in a broader context.
01:14:11Earth and its biosphere
01:14:12have experienced
01:14:13dramatic changes before.
01:14:16Life as a whole
01:14:16has proven remarkably resilient.
01:14:19But individual species,
01:14:21ecosystems,
01:14:22and climate regimes
01:14:23can change dramatically
01:14:25when atmospheric chemistry
01:14:26shifts beyond certain thresholds.
01:14:29The Carboniferous
01:14:30was a world of fire
01:14:32where even wet vegetation
01:14:34could burn
01:14:34in the oxygen-rich air.
01:14:36Our future may be
01:14:37a world of heat
01:14:38where increased greenhouse gases
01:14:41trap more of the sun's energy.
01:14:43Different drivers,
01:14:44different outcomes,
01:14:45but both demonstrate
01:14:46the profound connection
01:14:48between atmosphere
01:14:49and biosphere.
01:14:51But perhaps the most compelling aspect
01:14:53of the Carboniferous oxygen story
01:14:56is what it reveals
01:14:57about the interconnectedness
01:14:59of Earth's systems.
01:15:01The atmosphere,
01:15:02biosphere,
01:15:02hydrosphere,
01:15:04and geosphere
01:15:04don't exist in isolation.
01:15:07They constantly interact,
01:15:08each shaping
01:15:09and being shaped
01:15:10by the others.
01:15:12The oxygen
01:15:12that enabled giant insects
01:15:14came from plants.
01:15:16Those plants emerged
01:15:18from an evolutionary history
01:15:19shaped by earlier
01:15:21atmospheric conditions.
01:15:23Their ability
01:15:23to transform the atmosphere
01:15:25through photosynthesis
01:15:27changed the planet's chemistry,
01:15:29which in turn
01:15:30created new evolutionary pressures.
01:15:34This complex web of feedbacks
01:15:37and interactions
01:15:38is what makes Earth
01:15:39a living planet,
01:15:41not just a rock
01:15:42with life on it.
01:15:45Modern Earth system science
01:15:47emphasizes these interconnections.
01:15:50We now understand
01:15:50that to study
01:15:51any aspect of our planet,
01:15:53whether climate,
01:15:54biodiversity,
01:15:55or atmospheric chemistry,
01:15:57we must consider
01:15:59the whole system.
01:16:00The Carboniferous oxygen peak
01:16:02and its subsequent decline
01:16:04provide a vivid example
01:16:06of how these systems interact
01:16:08over geological timescales.
01:16:11When we look at
01:16:12a modern dragonfly
01:16:13with its incredible
01:16:15aerial agility
01:16:16and predatory precision,
01:16:18we're seeing
01:16:18the descendant of giants.
01:16:20The basic body plan,
01:16:22the respiratory system,
01:16:23the compound eyes,
01:16:24the predatory lifestyle,
01:16:26all were established
01:16:27hundreds of millions
01:16:28of years ago
01:16:29when dragonfly-like
01:16:31meganeura
01:16:32ruled the Carboniferous skies.
01:16:35Today's dragonflies
01:16:37are smaller
01:16:38but no less impressive.
01:16:40Their flight capabilities
01:16:41and hunting success rates
01:16:43remain unmatched
01:16:44in the insect world.
01:16:47Similarly,
01:16:47when we examine
01:16:48modern millipedes
01:16:49or scorpions,
01:16:51we're looking at
01:16:51the diminutive relatives
01:16:53of once-massive arthropods.
01:16:55They've retained
01:16:56many of the adaptations
01:16:57that served
01:16:58their giant ancestors,
01:17:00just scaled down
01:17:01to match the constraints
01:17:03of modern atmospheric conditions.
01:17:06This evolutionary continuity
01:17:08connects us directly
01:17:10to that alien world
01:17:12of 300 million years ago.
01:17:14The Carboniferous
01:17:15isn't just a remote period
01:17:17in Earth's history.
01:17:18It's present in the DNA
01:17:20of countless organisms
01:17:21around us,
01:17:22in the coal that still powers
01:17:24much of our civilization,
01:17:26and in the oxygen
01:17:27we breathe.
01:17:29The study of this
01:17:30ancient hyperoxic world
01:17:32continues to yield
01:17:34new insights.
01:17:35Recent research suggests
01:17:37that elevated oxygen levels
01:17:39may have played a role
01:17:40in the evolution
01:17:41of complex flight behaviors
01:17:43in insects.
01:17:44The extra oxygen
01:17:45would have provided
01:17:46more metabolic energy,
01:17:48potentially allowing
01:17:49for the development
01:17:50of sophisticated
01:17:51neural control systems
01:17:53for flight.
01:17:55Other studies indicate
01:17:56that the transition
01:17:57from high to low oxygen
01:17:59at the end
01:18:00of the Carboniferous
01:18:01may have driven innovations
01:18:03in respiratory efficiency
01:18:04across multiple animal groups.
01:18:07as oxygen became
01:18:08less abundant,
01:18:10natural selection
01:18:11favored organisms
01:18:12that could make better use
01:18:13of what was available.
01:18:15This may have contributed
01:18:16to the development
01:18:17of more efficient lungs
01:18:18in early reptiles,
01:18:20setting the stage
01:18:21for the active,
01:18:22high-metabolism lifestyles
01:18:24of later dinosaurs,
01:18:25birds,
01:18:26and mammals.
01:18:28There's even evidence
01:18:29that changing oxygen levels
01:18:31influenced the evolution
01:18:32of animal behavior.
01:18:34Higher oxygen allows
01:18:35for higher metabolic rates
01:18:37which in turn
01:18:38enable more active lifestyles.
01:18:41The predatory strategies
01:18:42of Carboniferous arthropods
01:18:44may have been shaped
01:18:45by the abundant energy
01:18:47available in their
01:18:48oxygen-rich environment.
01:18:51As oxygen declined,
01:18:52new behavioral adaptations
01:18:54would have been necessary.
01:18:56Changes in hunting strategies,
01:18:58activity patterns,
01:19:00and energy budgets.
01:19:02These ongoing discoveries
01:19:04remind us
01:19:05that the Carboniferous Oxygen Peak
01:19:07wasn't just an isolated phenomenon.
01:19:10It was part of Earth's
01:19:11long atmospheric history,
01:19:14a history that continues
01:19:15to unfold today.
01:19:17The current composition
01:19:18of our atmosphere
01:19:19with its 21% oxygen,
01:19:2278% nitrogen,
01:19:25and trace gases,
01:19:26including the all-important
01:19:28carbon dioxide,
01:19:30represents the current
01:19:31equilibrium
01:19:32in this dynamic system.
01:19:35Will this equilibrium
01:19:36hold?
01:19:37Human activities
01:19:38are now a significant factor
01:19:40in atmospheric chemistry,
01:19:42particularly through
01:19:43greenhouse gas emissions.
01:19:45While our impact
01:19:46on oxygen levels
01:19:47remains minimal,
01:19:48our effect on carbon dioxide
01:19:50and methane
01:19:51is substantial.
01:19:52Just as the Carboniferous
01:19:54demonstrates how
01:19:55atmospheric change
01:19:56can drive biological change,
01:19:58our current situation
01:20:00suggests that we're
01:20:01conducting an unplanned
01:20:02experiment with Earth's systems.
01:20:05The lesson from the Carboniferous
01:20:07isn't that atmospheric change
01:20:09is inherently bad.
01:20:11Earth's atmosphere
01:20:12has never been static.
01:20:14Rather,
01:20:14it's that rapid change
01:20:16can drive extinctions
01:20:17and ecological disruptions
01:20:19when organisms
01:20:20don't have time
01:20:21to adapt.
01:20:22The transition
01:20:23from the Carboniferous
01:20:24to the Permian
01:20:25occurred over millions
01:20:26of years,
01:20:27allowing for evolutionary
01:20:28responses.
01:20:30Today's changes
01:20:30are happening
01:20:31orders of magnitude
01:20:32faster.
01:20:34Yet,
01:20:35there's also hope
01:20:36in the Carboniferous story.
01:20:38It shows that
01:20:38Earth's systems
01:20:39tend toward
01:20:40new equilibria.
01:20:42When oxygen
01:20:43rose too high,
01:20:44fires increased,
01:20:45limiting further
01:20:46oxygen accumulation.
01:20:48When lignin-degrading
01:20:50fungi evolved,
01:20:51they brought the
01:20:52carbon cycle
01:20:52back into balance.
01:20:55Earth's history
01:20:56is full of such
01:20:57feedback mechanisms
01:20:58that moderate
01:20:59extreme changes.
01:21:01Understanding these
01:21:03mechanisms is crucial
01:21:04as we navigate
01:21:05our own impact
01:21:06on the planet.
01:21:07By studying how
01:21:08Earth responded
01:21:10to past atmospheric
01:21:11changes,
01:21:12we gain insights
01:21:13into how it might
01:21:14respond to current
01:21:15and future changes.
01:21:17This knowledge
01:21:17informs not just
01:21:19climate science,
01:21:20but conservation
01:21:21biology,
01:21:22environmental policy,
01:21:24and even space
01:21:25exploration.
01:21:27The giant insects
01:21:28of the Carboniferous
01:21:29were never meant
01:21:30to last forever.
01:21:32They were the
01:21:32products of a
01:21:33specific atmospheric
01:21:34moment,
01:21:36a window of
01:21:36opportunity created
01:21:38by a temporary
01:21:39imbalance in Earth's
01:21:40carbon cycle.
01:21:42When that imbalance
01:21:43was corrected by
01:21:44by the evolution
01:21:45of new
01:21:45decomposers,
01:21:47the window closed
01:21:48and the giants
01:21:49disappeared.
01:21:51But they weren't
01:21:51evolutionary failures,
01:21:53they were supremely
01:21:54well adapted
01:21:55to their time
01:21:56and place,
01:21:57exploiting the
01:21:58unique conditions
01:21:59of their
01:22:00hyperoxic world.
01:22:01Their descendants
01:22:02continue to thrive
01:22:03today,
01:22:04having adapted
01:22:05to changing conditions
01:22:06over hundreds
01:22:07of millions
01:22:08of years.
01:22:09This perspective
01:22:10offers a profound
01:22:12insight about
01:22:13life on Earth.
01:22:14Success isn't
01:22:15about permanence.
01:22:16Nothing in evolution
01:22:17is permanent.
01:22:19It's about adaptation,
01:22:20about finding
01:22:21opportunities in
01:22:22changing conditions.
01:22:24The Carboniferous
01:22:25giants did exactly
01:22:26that,
01:22:27thriving in their
01:22:28oxygen-rich world
01:22:29for tens of
01:22:30millions of years
01:22:31before conditions
01:22:32changed again.
01:22:34As we face
01:22:35our own period
01:22:36of rapid
01:22:36environmental change,
01:22:38this insight
01:22:39becomes increasingly
01:22:40relevant.
01:22:41The question
01:22:42isn't whether
01:22:43Earth's atmosphere
01:22:44and climate
01:22:44will change.
01:22:46They always have
01:22:47and always will.
01:22:48The question
01:22:49is how we respond
01:22:50to those changes,
01:22:51both as a species
01:22:52and as stewards
01:22:54of the biosphere.
01:22:56The Carboniferous
01:22:57oxygen peak
01:22:58was a biological
01:22:59creation,
01:23:00the result of
01:23:01plants producing
01:23:02oxygen faster
01:23:03than it could
01:23:04be consumed.
01:23:05Its end
01:23:06was equally
01:23:07biological.
01:23:07the evolution
01:23:08of decomposers
01:23:10that could
01:23:10break down
01:23:11lignin
01:23:11and return
01:23:12carbon to
01:23:13the atmosphere.
01:23:14In both cases,
01:23:16life shaped
01:23:17the atmosphere,
01:23:18which in turn
01:23:19shaped life.
01:23:21Today,
01:23:21humans have become
01:23:22a geological force
01:23:24capable of altering
01:23:25atmospheric chemistry
01:23:27at a global scale.
01:23:29This gives us
01:23:29a responsibility
01:23:30unique in
01:23:31Earth's history,
01:23:32the ability
01:23:33to consciously
01:23:34shape the future
01:23:35of our atmosphere
01:23:36and, by extension,
01:23:38the evolutionary
01:23:39trajectories of
01:23:40countless species,
01:23:41including our own.
01:23:43The legacy of the
01:23:44Carboniferous lives on,
01:23:46in the coal we burn,
01:23:48in the insects that
01:23:49buzz around us,
01:23:50and in the oxygen
01:23:51we breathe.
01:23:52By understanding
01:23:53this ancient
01:23:54hyperoxic world
01:23:56and its eventual
01:23:57transformation,
01:23:58we gain perspective
01:23:59on our own moment
01:24:00in Earth's
01:24:01long atmospheric
01:24:02history.
01:24:04We walk
01:24:05a quieter world
01:24:06now.
01:24:07The giants
01:24:08are gone,
01:24:09but their stories
01:24:10are still written
01:24:11in stone,
01:24:12in coal seams,
01:24:13in the genomes
01:24:14of their descendants,
01:24:15and in the very
01:24:16composition of the air
01:24:18around us.
01:24:19The Carboniferous
01:24:20wasn't just a strange
01:24:21chapter in Earth's
01:24:22history.
01:24:23It was a moment
01:24:24when the air
01:24:25itself changed
01:24:27what life could be,
01:24:28when creatures
01:24:29that seem impossible
01:24:30to us today
01:24:31were simply normal.
01:24:33And that perspective
01:24:34that Earth
01:24:35has been many
01:24:36different worlds
01:24:37over its long
01:24:38history is perhaps
01:24:40the most valuable
01:24:41insight of all.
01:24:42It reminds us
01:24:43that our current
01:24:44world isn't the
01:24:45only possible one.
01:24:47Earth has been
01:24:47and will be
01:24:48many things.
01:24:50The Carboniferous,
01:24:51with its giant
01:24:52insects and
01:24:53oxygen-rich air,
01:24:54is just one chapter
01:24:56in that ongoing
01:24:57story,
01:24:58a reminder of how
01:24:59thoroughly our planet
01:25:00can reinvent itself
01:25:01given enough
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