00:0166 million years ago, an asteroid the size of a city slammed into the earth, and the dinosaurs died.
00:07Case closed.
00:08That is the story you were told as a child.
00:11And it is almost certainly not the whole truth.
00:14Here's the problem.
00:15The more fossils we dig up, the more the classic story falls apart.
00:19And the single most damaging crack in it is this, when that asteroid hit, the earth may already have been
00:24dying.
00:25Let's start with how hard it is to kill something that big.
00:28Humans have existed for about 300,000 years.
00:32Dinosaurs existed for 180 million years.
00:35For 160 million of those, they ruled every continent on the planet.
00:39They dominated this world 500 times longer than we have.
00:43And you're telling me a single rock ended all of that?
00:46Something doesn't add up.
00:48So let's look at where the asteroid actually landed, and, more importantly, what was already happening before it did.
00:54The impact site is in the Gulf of Mexico.
00:56But the other disaster was in India.
00:59Today, western India is covered by a formation called the Deccan Traps, one of the largest volcanic regions on earth.
01:06But it wasn't a single volcano.
01:08It was an entire region of ground that cracked open, and then for hundreds of thousands of years, lava poured
01:13out.
01:14Layer after layer.
01:16Study after study suggests this went on for more than 700,000 years.
01:20The scale is almost impossible to picture.
01:23The lava covered half a million square kilometers, larger than Spain.
01:27In places, it is more than 2 kilometers deep.
01:30Stand at the bottom and look up, and you are facing a wall of stone 600 stories high, built one
01:35eruption at a time.
01:36Now here is the key question.
01:38When did it start?
01:40Because if the eruptions began before the asteroid, then the dinosaurs were already in trouble.
01:45The answer comes from tiny crystals found in volcanic ash.
01:49They're called zircons.
01:51When they form, they trap uranium inside them.
01:54And uranium decays into lead at a fixed, clock-like rate.
01:57So every zircon is a little stopwatch that started ticking the moment it solidified.
02:02And it keeps accurate time for tens of millions of years.
02:06Researchers used these zircon clocks to date the decanash layers.
02:09The result was startling.
02:11The eruptions began while the asteroid was still traveling through space.
02:15There was a gap of more than 200,000 years between the start of the eruptions and the impact.
02:20200,000 years, roughly the entire length of time modern humans have existed.
02:25Now, volcanoes don't kill instantly.
02:28They kill slowly, and they kill in two opposite ways at once.
02:32In the short term, sulfur particles reflect sunlight and cool the planet.
02:36In the long term, carbon dioxide traps heat and warms it.
02:40Both at the same time.
02:41So for hundreds of thousands of years, the climate swung violently back and forth,
02:46hot, then cold, then hot again.
02:48And for an ecosystem, that is the worst possible thing.
02:52It's not endless cold that breaks a species.
02:54It's the constant switching.
02:56Every generation is adapted to the last climate, and the next one arrives before anything can adjust.
03:02It's like a fever that never quite breaks, for 200,000 years.
03:06Layer by layer, the dinosaur's margin for survival was worn thin.
03:10So what state were the dinosaurs actually in?
03:13Think of it like a boxer who has already gone 15 rounds.
03:17He's still standing.
03:18He's still dangerous.
03:20But he has nothing left in reserve.
03:22He can survive a lot of things, just not one more hard punch.
03:26Then the punch came.
03:28A rock roughly 10 kilometers wide, hitting at the worst possible angle, in the worst possible place.
03:34The immediate effects were brutal.
03:35The impact threw enormous amounts of dust and sulfur into the atmosphere, blocking sunlight for years.
03:42Global temperatures dropped.
03:43Plants died first, because they need light.
03:46Then the plant eaters starved.
03:48Then the meat eaters that fed on them.
03:51The food chain collapsed from the bottom up.
03:53And that explains one of the strangest patterns in the fossil record.
03:57Most of the animals that died were the big ones.
04:00The larger the body, the more food it needs every day, and the more territory it requires.
04:05In a world where almost nothing is left, being huge is a death sentence.
04:09The survivors followed a very clear set of rules.
04:12Be small.
04:14Be able to burrow.
04:15Don't be picky about what you eat.
04:18Live on seeds, on rotting material, on anything that falls your way.
04:22Our own ancestors, the early mammals, were exactly that, about the size of a squirrel,
04:27hiding underground, feeding on whatever they could find.
04:30Creatures in the water did better, too.
04:33Ocean temperatures were more stable, and there was always something to eat.
04:36But here is the part almost nobody mentions.
04:39The dinosaurs never actually went extinct.
04:42Birds are dinosaurs.
04:44They are the surviving branch of a group called the theropods.
04:47Every one of the more than 10,000 bird species alive today is a direct descendant of those dinosaurs.
04:53So the next time a bird wakes you up outside your window at dawn, remember, you are listening to a
04:57living dinosaur.
04:59After the impact, the earth went through a genuinely strange period.
05:03In rock layers across North America and New Zealand, researchers have found the same signature.
05:08In some layers, fungal spores make up more than half of all the pollen in spores present.
05:13Fungi don't need sunlight.
05:15They feed on dead things.
05:17And at that moment, the world was covered in dead trees and dead animals.
05:21The sky stayed dark for years.
05:23The planet was, briefly, one enormous graveyard.
05:27And here is where the case gets even stranger.
05:30This mystery still isn't solved.
05:32In recent years, scientists using seismic data beneath the coast of West Africa found a crater more than 9 kilometers
05:38wide, dating to almost exactly the same time as the Chicxulub impact.
05:42One theory is that the asteroid had already broken apart before it reached Earth, and the fragments struck in quick
05:47succession.
05:48This isn't wild speculation.
05:50In 1994, we watched comet Shoemaker-Levy 9 get torn apart by Jupiter's gravity and slam into the planet as
05:57a chain of separate impacts, live, through our telescopes.
06:00But whether those two craters were days apart, months apart, or thousands of years apart, we still can't say.
06:06We need to bring up the rock from the bottom of that crater to know.
06:10So this is where the case stands now.
06:12It wasn't simply a rock that killed the dinosaurs.
06:15It wasn't the volcanoes alone, either.
06:17The Earth was first stressed for more than 200,000 years by the eruptions in India.
06:22The climate swung back and forth until the ecosystem had almost no margin left.
06:27And then, on a spring morning, a rock struck at the worst angle, in the worst possible spot.
06:32One biologist proposed a calculation that gives you chills.
06:35The Earth rotates once a day, and most of that surface is ocean.
06:39If that rock had landed almost anywhere else, deeper water, thicker ocean crust, the planet might have shrugged it off.
06:46It hit shallow water, where the sulfur-rich rock could be vaporized and thrown into the sky.
06:51If it had hit deeper ocean, less material would have launched, the sky would have stayed clearer, and maybe the
06:56dinosaurs would have survived.
06:58And the reason we can reconstruct a single morning 66 million years ago to this level of detail is not
07:03that we found more dinosaurs.
07:05It's that we found new clocks.
07:07Zircons in volcanic ash are clocks.
07:09Growth rings in fossil bones are clocks.
07:12Cosmic debris in seabed sediment is clocks.
07:15We didn't find a new story.
07:17We found new instruments, and pointed them at the old crime scene.
07:21And the sequence turned out to be completely different from what we assumed.
07:25160 million years.
07:27That's how long dinosaurs ruled this planet.
07:30They survived continents splitting apart.
07:32They survived sea levels rising and falling.
07:35They survived countless climate reversals.
07:38And they ended on a single morning.
07:40They weren't weak.
07:42They were simply unlucky enough to be there on that day.
07:45And the only reason we're sitting here, discussing it, is that 66 million years ago, on a spring morning, that
07:51rock hit exactly the wrong spot.
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