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Ancient Australian fossils offer clues as to how four-legged animals came to dominate Earth.....
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00:00Over four billion years in the making.
00:06An island adrift in southern seas.
00:10It's Australia.
00:12The giant down under.
00:16A young nation.
00:19With all the gifts of the modern age.
00:22That move beyond the cities.
00:26And an ancient land awaits.
00:30One nearly as old as the earth itself.
00:39Australia is a puzzle.
00:42Put together in prehistoric times.
00:47And the clues that unlock the mystery
00:49can be found scattered across Australia's sunburnt face.
01:00I'm Richard Smith.
01:02And this is an amazing country.
01:07I'll show you that every rock has a history.
01:11Every creature.
01:12A tale of survival against the odds.
01:16Join me on an epic journey across a mighty continent.
01:22And far back in time.
01:25Of all continents on earth,
01:28none preserve the great saga of our planet
01:30and the evolution of life quite like this one.
01:34Nowhere else can you so simply jump in a car
01:38and travel back to the dawn of time.
01:42In this episode.
01:44The world above water has sat silent and lifeless.
01:50But now armies storm the beaches.
01:53And biology conquers the world.
01:55It's the battle for life on earth.
01:59The struggle for legs and lungs.
02:03Sunlight and shelter.
02:05Even the quest for sex.
02:08From Australia's ancient stones
02:10comes the story of our world.
02:15Australia's first four billion years.
02:19Life explodes.
02:22Right now on NOVA.
02:39Major funding for NOVA is provided by the following.
02:45The David H. Koch Fund for Science.
02:48Supporting NOVA and promoting public understanding of science.
02:55And by the Corporation for Public Broadcasting.
03:00And by contributions to your PBS station from viewers like you.
03:24If Australia seems a little tired and worn,
03:27it's because she's seen a lot happen over the course of her long life.
03:42In the last episode,
03:44our journey down the road of time
03:46began with the Earth's fiery birth.
03:49Four and a half billion years ago.
03:54We passed the first fumbles of life
03:57in the waters skirting Australia's ancient shoreline.
04:04Along the way,
04:05we've seen the planet change from poisonous to pleasant.
04:10And the first animals begin to swim the seas.
04:17Yet, save for a thin smear of slime and bacteria
04:20along the soggiest of margins,
04:24all the continents themselves had lain bare for over four billion years.
04:32In terms of the lifetime of a continent,
04:35Australia and the world around it is still an infant,
04:39still attached to its motherland,
04:41the great supercontinent Gondwana,
04:44and still a blank canvas on land.
04:48Your destination is the Paleozoic.
04:52Now, with 90% of Earth history behind us,
04:56it's time for conquest.
05:13The tremendous explosion of life that began in the oceans of the Cambrian
05:17was still going strong at the dawn of the Ordovician,
05:19the second of the six great periods that make up the Paleozoic.
05:24And it was in Ordovician oceans
05:26that a second wave of animal experimentation began as well.
05:30One that ultimately would lead to the first Australians coming ashore.
05:37With the seas now crowded with life,
05:39the first tentative footsteps onto land were not far away.
05:48Now, at the time,
05:49Australia was just one of an exotic collection of lands,
05:52including India, Africa, South America and Antarctica,
05:56that today we call the supercontinent Gondwana.
06:01Australia's position was just about here.
06:03Right at the tip,
06:06just north of the equator,
06:07and mostly underwater.
06:14Oceans were rising around the planet,
06:17and seawater flooded in across parts of Central Australia.
06:24At the time,
06:26the sea of sand we know today as the Simpson Desert
06:29was slap-bang in the middle of the Larrapinta Seaway.
06:33A tongue of warm ocean water that licked right across the country.
06:41Back then, this bouncy drive would have been a bumpy boat crossing.
06:51As the rising waters swept in, they carried a rich bloom of plankton.
06:57Food for some of the earliest fish to swim in the sea.
07:03And they swam right here, right above me.
07:11The last vestiges of the old Larrapinta sea floor
07:15lie tumbling from the top of the mesa-shaped hills of the Simpson Desert.
07:21Even in the best of seasons like this,
07:24the Simpson is a harsh, unforgiving landscape.
07:30Now, you probably wouldn't expect to find the world's earliest fish
07:34in the dead centre of the driest inhabited continent on the planet today.
07:39But it was on the side of this hill in the Simpson Desert
07:42where the fossil of Arendaspis lay waiting to be discovered.
07:50We only know Arendaspis from the bony headplates and body scales it left behind.
07:57Enough to tell that this was a fish with a simple tail and no real fins.
08:03Nor did fish like Arendaspis have jaws or even teeth.
08:08They probably just slurped in whatever morsels they could find.
08:17But don't underestimate the significance of this fish.
08:22This was an animal with a backbone.
08:25It's one of the first vertebrates,
08:27so we can all trace our ancestry back to an animal like this.
08:37But giant invertebrates ruled these Ordovician seas.
08:41And to them, Arendaspis was just a bite-sized snack.
08:50While the first fish took to swimming out of danger,
08:53their invertebrate foes would soon be flexing their leg muscles
08:58in a different way.
09:00Time to put the foot down
09:02and head for the seaside in the Silurian.
09:16On a remote stretch of the Western Australian coast,
09:19the 21st century Indian Ocean eats away at an ancient Silurian shoreline.
09:28Wind and water have exposed the burrows of long-gone animals
09:32in the sandy coastal cliffs.
09:37The original inhabitants of the burrows remain a mystery.
09:40But not the predators attracted by such rich pickings
09:44along the prehistoric shoreline.
09:51Clues to their identity are revealed in the rocks
09:55of nearby Murchison Gorge.
09:58Here, the river has sliced deep into the Silurian past.
10:05The Murchison Gorge back in the Silurian
10:08wasn't a gorge at all, of course.
10:10It was a vast estuarine floodplain
10:13with rivers winding down from the hills in the distance,
10:16carrying sand into the sea.
10:18But for the first time in the history of the planet,
10:21those Silurian shorelines down there were alive with animal activity.
10:32This may not have been a good time to take the kids to the beach.
10:38Armies of sea scorpions were massing in the shallows.
10:43Known to palaeontologists as Eurypterids,
10:47some of these intimidating arthropods grew as long as a man is tall,
10:52and they bristled with armoured legs and fearsome claws.
10:59Far less threatening was this bloke.
11:03Calbaria was probably an ancestor of modern crustaceans
11:07and grew about as long as a king prawn.
11:11Whether in search of food, a safe place to mate,
11:15or simply to avoid the nasty neighbours,
11:18Calbaria clambered ashore.
11:24And left clear imprints of its many tiny feet in the rocks.
11:34A descent into Murchison Gorge
11:37takes you back to those ancient Silurian shorelines.
11:43Down here, it soon becomes clear
11:46that the sea scorpions followed Calbaria ashore.
11:52This is what we call Track Central.
11:55I can see why.
11:56There are tracks everywhere.
11:58This is probably the best site in the park
11:59to look at these Eurypterid tracks.
12:02Our animals come through here.
12:03So in shallow water?
12:04Shallow water.
12:05OK, it's been slipping and sliding a little bit
12:07as it comes around the corner.
12:08That's exactly right.
12:09But here, I mean, I can see clearly
12:11this is kind of sloppy-looking track here.
12:13Yep, it is.
12:14But once you come over here,
12:15you start seeing really discreet footprints.
12:18Clear, graphic demonstration of a creature
12:21walking out of the water and onto dry land.
12:24And where we are here in the depth of the gorge,
12:27we're in the oldest of the Silurian sediments in this area.
12:30Quite a historic little spot you've got here.
12:32Very, very.
12:35These trackways offer some of the oldest evidence
12:38for animals on land.
12:41And even though these formidable beasts
12:44could not stray far from the water's edge,
12:46a beachhead had been established.
12:52So this seems to be how the animal invasion of the land began,
12:57with a scary assortment of arthropods with attitude
13:01slinking and scuttling ashore
13:02onto the wet sands of a new frontier.
13:07But this wasn't just a continent to exploit.
13:10There was a whole planet for the taking.
13:18Waiting beyond the breakers
13:20were all the wide brown lands of Earth.
13:30Australia, already under animal assault,
13:34found itself centre stage
13:36for the waves of invasion and conquest that would follow.
13:44But animals were not going to get far inland
13:48without help from plants.
13:55They, too, came out of the sea.
13:58First as slime,
14:00then as low-spreading things that clung to dampness.
14:06Seaweeds captured the shoreline.
14:08Then tiny forests of lichens, liverworts and mosses
14:13pioneered the moving land.
14:25Today, we take for granted the plants around us.
14:29It's their oxygen we breathe.
14:31Their food we eat.
14:34But the land can be a tough, dry place to live.
14:38And any plant going to make it big out here
14:41needed a thick skin
14:43and a little internal fortitude.
14:47Just such a plant first took root somewhere around here.
15:05If you thought that this was just another ordinary roadside cutting,
15:09on a pretty but ordinary country road,
15:12well, of course, you'd be dead wrong.
15:13It was here near Yeay in Victoria
15:16that fossils of some of the world's earliest land plants were found.
15:21Indeed, these rocks contain the first signs
15:25of the greening of Gondwana.
15:29Just amazing.
15:34This is Barra-Gwenathia.
15:37Possibly the oldest true land plant in the world.
15:41Not much to look at, perhaps.
15:43But with green leaves and a stem to carry sap internally
15:47and to support its weight,
15:49the world above water was its oyster.
15:54In life, it would have looked much like this.
15:58This is a lycopod, or club moss, as was Barra-Gwenathia,
16:02rising out of the water in a coastal bog in Queensland today.
16:11These are the direct descendants of the green revolutionaries
16:15who changed the face of the planet.
16:20If you look closely,
16:22you can see many of these Silurian-type plants
16:25still clinging on in damp corners around the country.
16:28Here's a rainforest Selaginella,
16:32a tropical tassel fern,
16:35a club moss in Tasmania,
16:38even a Silotum in Sydney.
16:46Plant life had by now engineered a solution
16:49to the ultraviolet radiation
16:51that had been sterilising the Earth's surface.
16:55An ozone layer, built from excess oxygen.
17:03The low spreading thickets provided the perfect humid cover
17:08for other arthropod forms like millipedes, centipedes and mites
17:12to make the transition to the land complete.
17:17Some mollusks even brought their own homes
17:21because it was still not a very welcoming place.
17:31While life was exploring the fringes,
17:34most of the Gondwanan supercontinent was dry,
17:38probably still quite bare,
17:41and almost certainly windy.
17:46The Larapinta Seaway had receded,
17:49leaving much of what is now central Australia
17:52resembling the Sahara Desert.
17:58And that desert became mountains.
18:21Titanic tectonic forces, operating over a span of 150 million years,
18:27buckled the Earth and pushed great folds of rock into the air.
18:39In their heyday,
18:41Central Australia's McDonnell Ranges
18:44would have been a mountaineer's dream,
18:47as high it's thought as any on Earth today.
18:53But Australia would never experience mountain building on this scale again.
19:19After a near eternity of erosion,
19:22the diminished remnants of the McDonnell Ranges
19:26still run in long jagged wrinkles
19:30across the heart of Australia.
19:44From the air, they protrude into this ancient landscape,
19:49like the bony skeleton over which the dry skin of a tired continent is draped.
20:11All other continents boast mighty mountain ranges.
20:16The Rockies, the Alps, the Andes, the Himalayas.
20:20But they're all relative newcomers,
20:24and mostly still growing.
20:32What sets Australia's landscape apart is its venerable antiquity,
20:38and its great flatness.
20:45Australia is actually quite remarkably flat.
20:48And when you look at it from space,
20:52it's not just flat, but it's apparently saucer-shaped.
20:58It's a saucer that holds many secrets for geologist Lisa Worrell.
21:04Her interest is not so much the bedrock of the outback,
21:07but the story of all its eroded remnants,
21:11accumulated over a vast gulf of time.
21:15We know parts of Australia have been exposed for millions,
21:20if not billions of years.
21:28We're part way through an ongoing geological story.
21:34The rivers that in Australia mostly drain inland
21:38are actually losing or have lost the ability
21:42to carry sediments out and down into the seas.
21:45So inland Australia is filling up with sediments.
21:58Outback Australia is drowning in sand.
22:05Head towards the coast in any direction from the red centre,
22:08and you cross oceans of these old, weathered sediments.
22:14It's the sort of landscape you should expect
22:17from the flattest continent on the globe.
22:23Travelling north-west, it's 700 miles
22:26before you reach the next significant patch of high rocky ground.
22:33The Kimberley.
22:40While mountains were still pushing skywards in the continent's heart,
22:45up here in Pernalulu National Park,
22:47others were already wearing down to nothing.
23:03CHOIR SINGS
23:08Epic tales of erosion and recycling lie behind most geological features
23:14in the Australian landscape.
23:21The sands and gravels that made the Bungle Bungle Ranges
23:25started arriving here about 375 million years ago.
23:30Dumped by rivers that wore away highlands far older and now long gone.
23:41This landscape was already second-hand, long before the rocks began eroding away
23:47into the famous striped beehive domes we see today.
23:56The distinctive striping of the rocks here is a dead giveaway to how the Bungle Bungles were formed,
24:02layer by layer, as mighty rivers wash sediment from distant mountain ranges to fill the basin.
24:13This unfolding landscape is a two-tone testament to change.
24:19Left as a parting gift by rivers that ran down into a Devonian tropical sea.
24:40300 dusty miles to the west of the Bungle Bungles,
24:43and you can run down to that same ancient sea.
24:48Once home to some of the most spectacular tropical reefs on the planet.
24:58Surprisingly, you can still visit these reefs today.
25:11I'm standing at the base of the Great Devonian Barrier Reef.
25:17These towering limestone cliffs were once towers of life
25:21rising into the clear sunlit waters of a colossal reef system that once circled the Kimberley.
25:32In both size and significance,
25:35the Devonian Reef rivalled modern Australia's Great Barrier Reef.
25:41Its limestone ramparts were once festooned with crinoids and corals, sponges and sea squirts,
25:48and many other creatures still found clinging on in tropical waters.
25:55That Devonian life is gone, but the Great Reef walls still stand to this day.
26:06It's easier to see from the air.
26:12In the same way that the Great Barrier Reef fringes the Queensland coast today,
26:18the Great Devonian Reef skirted in a sweeping curve around the Kimberley hinterland
26:22for perhaps 600 miles.
26:30Reef after reef line up across the landscape as if a giant bath plug had been pulled.
26:47The Great Barrier Reef
26:48At Tunnel Creek, one such stream has carved its way right through the Devonian Limestone Range.
26:59It's a deliciously cool change from the sweltering heat outside
27:04and offers dark access to the very heart of the reef itself.
27:18A whole suite of reef building organisms built this Great Devonian Reef above me.
27:23You can see a lot of their ghostly remains in the rock still.
27:27Sponges, stromatolites, corals, strange extinct things called stromatoporoids.
27:34But the real stars of the show here weren't the things that made the reef,
27:39but the things that swam around outside it.
27:41Things with fins.
27:43Because this was the great age of the fishes.
27:53It was in the Devonian that for the first time, fish filled the oceans.
28:00Fish of all shapes and sizes.
28:04Just not quite the shapes and sizes we see today.
28:17Like the reefs themselves, the fish of the Devonian Northwest are amazingly well preserved.
28:26Protected in limestone nodules scattered across nearby Gogo Station.
28:31Ow!
28:35You don't get a lot of bites around here.
28:38About one nodule in every thousand yields a good fossil strike.
28:47But whenever you catch a Gogo fish, it's always something special.
28:55Oh wow!
28:56That's a lot of bone.
28:58That's all bone there.
28:59That's some very large plates.
29:02So what do you think that is, Gavin?
29:05It's clearly a large placoderm.
29:09Probably a big arthrodite.
29:10That's why.
29:20Kings of the Devonian Seas were the placoderms.
29:27Fish had moved on since the days of Arendaspis.
29:31Now they had jaws, fins and teeth to go with their bony headplates.
29:39The front part of the body was covered in these bony plates.
29:45And then the tail would be pretty much shark-like.
29:50They were in fact very agile, successful predators.
29:55They had a highly developed sensory system.
29:58Some of them had electrosensory perception, like modern sharks and rays.
30:04Many of these fossil features have been preserved in fabulous 3D.
30:10Oh look, there's some ridging.
30:12The Gogo nodules have protected the fossils from being crushed.
30:16Do you think it might be a holonema?
30:18A nice bath and acid's going to clear it up.
30:21Soak it in some water and scrub it with it.
30:23Toothbrush, it'll be much water.
30:24I don't know, if I'm not getting a shower at night, this fish certainly isn't.
30:35It's only once the limestone nodule is dissolved away in acid in the lab that the fossilised fish within come
30:42back to life.
30:45In astonishing detail.
30:52Scales, teeth, eye sockets, brain cases, bones and fin rays.
30:58The fish are all so fabulously well preserved for their age that even soft body bits can be made out.
31:06In more ways than one, these are pretty sexy fossils.
31:13Well this one here is particularly interesting because it's one of the few male fossils that we have.
31:19And we can tell that because it has this clasper.
31:22What, like in a shark?
31:23Very much like a shark.
31:25This bony tube structure is the oldest confirmed male appendage.
31:31A fishy private part for impregnating a female.
31:40The Devonian was an important time for vertebrate life.
31:44With many biological experiments underway.
31:48Including the all-important vertebrate sex.
31:57Even today, sex in the sea can be a bit of a hit or miss affair.
32:03A trade-off between precision and plenty.
32:09Without coupling and live birth, vulnerable progeny sink or swim on their own.
32:18Not a strategy destined for success on land.
32:28This is a portrait of the world's oldest preserved mother with child.
32:34And we have the fossil to prove it.
32:38And this is perhaps our most famous discovery to date.
32:42This is the mother fish.
32:43And this is the real kind of clincher we had that you could have live birth.
32:48And it's this little structure here right around the bottom.
32:52And that is the umbilical cord which is attaching the mother to her unborn embryo.
33:00My goodness, that's the world's earliest umbilical cord we know of.
33:05That is, it's the world's earliest evidence of live birth in any vertebrate.
33:12Our backbone ancestors were making all the right moves.
33:18Already on the road to becoming social, smart and sexy.
33:25And they were everywhere.
33:31As rain fell on Australia's newly constructed east, rivers ran back down towards the sea.
33:38Filling the freshwater lakes and backwaters of the new coastal landscape.
33:46Throw a line into one of those Devonian rivers and you would have caught plenty of fish that looked almost
33:52identical to this.
33:58Whoa, hi big guy.
34:01Oh, look at you.
34:02Aren't you something special?
34:04Now this is something truly special.
34:07A living link to our fossil past.
34:09It's the Queensland lungfish, Neotheratidus fosteri.
34:13And I'm trying to hold him my hope.
34:16Now, he is the most primitive of the handful of lungfish that still swim on planet Earth.
34:22Think about it for a moment.
34:25These guys were already ancient history, a hundred million years before the first dinosaurs walked the Earth.
34:32And if you're worried about that fish out of water thing,
34:36these guys are called lungfish for a reason.
34:39They're built for it.
34:41There you go matey, off you go.
34:55When lungfish moved from the sea into fresh water in the Devonian, they brought with them the ability to breathe
35:01with or without gills, when the going got tough.
35:08It's a skill that still stands these remarkable living fossils in good stead.
35:14They live on in just a few river systems in South East Queensland.
35:19And when oxygen levels fall, they can switch to gulping air from the surface.
35:27It's a strategy that has doubtless allowed them to struggle through more than one Australian drought.
35:35Not all fish have been so lucky.
35:45As far as we can tell, drought is a problem that has plagued the country for at least 360 million
35:52years.
35:55We know this because in 1955, the local council sent a bulldozer to smooth out a bad bend on the
36:03Canoundra to Goolagong Road.
36:18Well, the bad bend in the Canoundra to Goolagong Road is still here.
36:22And you wouldn't know it to look at it, but I've just parked right on top of one of the
36:27most spectacular Devonian freshwater fish sites in the world.
36:32The roadworks inadvertently lifted the lid on Australia's oldest known outback waterhole.
36:43When a paleontological team returned to open the site,
36:46thousands of fish tumbled out.
36:52They were lying on the slabs just as they had been the day they all died together when their waterhole
36:59dried up.
37:03Like their saltwater go-go cousins, many were armour-plated placoderms.
37:16There were lungfish here as well.
37:19And another related group of fishes with four-lobed fins that we humans should be very thankful for.
37:33Of the 4,000 or more fish uncovered on these Canoundra slabs, this one is special.
37:41It's been given the name Canoundra grossi, after the town of course, but its real claim to fame are the
37:48features that it shares with those fish-like animals that were leaving the water behind.
37:55A single pair of external nostrils suggests it too could breathe with both lungs and gills.
38:04And it was one of the lobed-finned fish.
38:06A group with four rim-like fins, with a bony internal structure we can recognise in our own arms and
38:14legs.
38:20It's not hard to imagine that somewhere in the drying Devonian waterhole at Canoundra, at least one of those fish
38:28might have got away.
38:31By walking onto land.
38:35And this is why.
38:38Hard evidence in the form of fossilised four-legged footprints, of about the same age, and found near the Genoa
38:46River in Victoria.
38:56It was a different Genoa River, but these early fish-like tetrapods, about three feet long, were among the first
39:04animals on Earth to feel the sand between their toes.
39:12It's not hard to see how the evolution of walking limbs might have come about.
39:20Many Australian fish species today are still testing out ways of getting about without swimming.
39:28This is the aptly named handfish.
39:32Hopping and skipping its way along the Derwent Estuary in Tasmania.
39:40And this, that master of the tropical mangrove, the mudskipper.
39:48However they'd managed it in the first place, amphibians soon walked out into the botanical wonderland of the Carboniferous.
40:10The Carboniferous saw all sorts of new plants putting down roots and pumping out oxygen at levels the planet had
40:18never seen before.
40:24Huge forests, especially in the Northern Hemisphere, helped push up oxygen levels in the atmosphere, perhaps 50% higher than
40:33today.
40:37The extra oxygen saw some invertebrates grow to enormous sizes.
40:43It allowed millipedes the size of snakes to scuttle across the land, and insects as large as seagulls to take
40:52to the air.
40:56The rich insect pickings on offer must have favoured the spread of the amphibians now moving through the landscape.
41:06But like their froggy descendants today, these ancestral four-legged animals needed to return to water to reproduce.
41:19Some time in the Carboniferous, the first reptiles overcame this limitation.
41:26Wrapping their eggs in a membrane blanket with a hard outer shell, reptiles could take a watery egg with them
41:33on their travels.
41:37It was a solution so successful that it allowed the many contemporary lizards of Oz to still claim the arid
41:46Australian outback as their own.
41:56There was yet another Carboniferous legacy left out here.
42:04The greening of the earth began to at least partly turn Australia red.
42:12The highly oxygenated atmosphere began to rust the iron-rich soils and rocks of the outback.
42:22And some rocks out here are bigger than others.
42:30It's very impressive.
42:32It's a fabulous monolith, isn't it?
42:34It's justly famous for being the largest bit of rock, lump of rock in the world.
42:40Yeah. And it's just gorgeous.
42:43And it's very red.
42:46The colour of weathered iron minerals like haematite.
42:52Many of the rocks of Australia are rusted.
42:56We know that we had oxidising rocks back to around the Permocarboniferous.
43:01That colouration of the landscape is in fact very old and very persistent.
43:12But at the end of the Carboniferous, just as world domination lay within the reptiles' grasp,
43:20the changing world threw up another great climate challenge.
43:31The drift of Gondwana saw Australia heading south and getting colder.
43:39It was more than just the location.
43:43The earth had slipped into another ice age.
43:47And Australia was covered in more ice than it would ever see again.
44:00By the time we reached the Permian, a deep chill had settled in.
44:06Ice carved its calling card on the country.
44:11Nowhere more clearly than the Floro Peninsula in South Australia.
44:22The bedrock here was scoured by glaciers.
44:28All these long scratches and grooves in this smooth surface were gouged by rocks and debris
44:33being dragged along at the bottom of an ice sheet flowing in this direction.
44:41What these rocks are telling us is that clearly if you look to the south of Australia back in the
44:46Permian,
44:47you wouldn't have seen the open ocean we see today.
44:50If you look back that way, you would have seen the mountains of Antarctica.
45:18It's incredible to think that if you travelled to Australia in the early Permian,
45:22the landscape probably looked much like this over at least the southern half of the continent.
45:29Evidence for ice can be found stretching across the country,
45:33from the Kimberley to the coast of Tasmania.
45:42But this cold landscape was not frozen solid like Antarctica.
45:50It was seasonally cold, more like a northern Alaska or Canada.
46:00Well, Permian Australia might have been freezing cold, but it was far from lifeless.
46:07These remarkable rocks on Moriah Island are just stuffed to the gunwales with shellfish.
46:13And nearly every one of the animals in the rocks here, and in the rocks behind me, and the cliffs
46:19in the distance,
46:20belong to one species of clam.
46:23This one, called Urodesma.
46:33What Australia's Permian Ocean lacked in diversity, it made up for with abundance.
46:44Life crowded the sea floor.
46:57It was the same story on land.
47:00And the proof can be found hidden underneath Australia's moist eastern seaboard.
47:07Much of it right under modern Sydney.
47:14Beneath the eucalypt forests that surround the city of Sydney today
47:18lie cool climate forests far more ancient.
47:22Welcome underground, gentlemen.
47:23Ground floor of the Permian.
47:29I'm heading half a mile down into a coal mine at Hellensburg on Sydney's southern outskirts.
47:40The seams of rich black coal here have been mined for longer than any other in the country.
47:50What you're looking at here is the exhumation.
47:53Half a kilometre underground of the dead black graveyard of a vast swampy forest that once stretched right across the
48:01Sydney basin.
48:02It's hard, messy, noisy work.
48:05But there's treasure in this coal.
48:07The raw energy of fossilised sunlight.
48:16Half the energy used to light Australian homes, fuel industry, cool beer and power this program comes from Permian plants
48:27buried faster than they decomposed over a quarter of a billion years ago.
48:42When scientists looked closely at these coal scenes, they found something not seen in the Australian forest growing so far
48:48above me today.
48:49The fossil leaves they encountered were found in alternating repeated layers.
48:56Every autumn it seems, these now blackened Permian coal forests were once a riot of colour.
49:10One tree above all others dominated the Permian forests.
49:16Glossopterus.
49:22Glossopterus had solved another part of the problem of reproducing on dry land by encasing its embryo in a protective
49:31seedy shell.
49:34So successfully, it turns out, that fossilised Glossopterus leaves are the botanical signature of all Gondwannon lands.
49:47The planet had come of age in the Permian.
49:53Here was a world with great oxygen producing forests, inhabited by animals with four legs.
50:01Insects had taken to the skies and the seas were brimming with animals.
50:09Life on Earth was going swimmingly well.
50:16And then, suddenly, everything went diabolically wrong.
50:30Well, the Permian came to a sudden and very sticky end, right here, at the greatest extinction boundary in the
50:38planet's history.
50:39Now, this black coal is the last coal to have been deposited anywhere on Earth in the Permian.
50:46The last of the great Gondwannon Glossopterus swamps.
50:50But it also marks the bitter end for over 80% of all species alive on the planet at the
50:57time.
50:58This truly was the world's greatest cataclysm.
51:07This figure is conservative.
51:11Some estimates have 95% of all species dead and gone.
51:17Wiped out in a geological blink.
51:30The trigger, it seems, did not come from outer space, but from underground.
51:38It's now thought massive volcanic eruptions in Siberia pushed CO2 levels sky-high and the planet into a runaway greenhouse
51:48crisis.
51:51These were the days when our living Earth nearly died.
51:58Acidified and stagnant, great swathes of the ocean festered.
52:04Toxic bacteria took over from plankton.
52:07And deadly hydrogen sulphide spilled into the skies.
52:16But with change, even of the calamitous kind, comes opportunity.
52:24And the Earth would soon echo to the thunder of giants.
52:34The adventure continues on NOVA's website, where you can watch other episodes of Australia's first four billion years.
52:41See video extras, hear from experts, and explore interactives.
52:45Find us at pbs.org slash NOVA.
52:48Follow us on Facebook and Twitter.
52:49On the next episode of Australia's first four billion years, dinosaur hunting down under.
52:55Big footprints. One there, another one there.
52:58Peer into the belly of a beast.
53:00And inside its stomach, we can see the vertebrae of its meal.
53:04Come face to face with bizarre creatures of a lost world.
53:09It's almost as if there's an independent experiment and evolution going on here.
53:13Monsters. Next time on Australia's first four billion years, on NOVA.
53:20Major funding for NOVA is provided by the following.
53:25The David H. Koch Fund for Science.
53:28Supporting NOVA and promoting public understanding of science.
53:34And by the Corporation for Public Broadcasting.
53:38And by contributions to your PBS station from viewers like you.
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54:10NOVA is also available for download on iTunes.
54:20The
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