Sixty-five million years ago the last of the non-avian dinosaurs went extinct. So too did the giant mosasaurs and plesiosaurs in the seas and the pterosaurs in the skies. Plankton, the base of the ocean food chain, took a hard hit. Many families of brachiopods and sea sponges disappeared. The remaining hard-shelled ammonites vanished. Shark diversity shriveled. Most vegetation withered. In all, more than half of the world's species were obliterated.
What caused this mass extinction that marks the end of the Cretaceous and the beginning of the Paleogene? Scientists have yet to find an answer. The one that does must explain why these animals died while most mammals, turtles, crocodiles, salamanders, and frogs survived. Birds escaped. So did snails, bivalves, sea stars (starfish), and sea urchins. Even hardy plants able to weather climate extremes fared OK.
Scientists tend to huddle around one of two hypotheses that may explain the Cretaceous extinction: an extraterrestrial impact, such as an asteroid or comet, or a massive bout of volcanism. Either scenario would have choked the skies with debris that starved the Earth of the sun's energy, throwing a wrench in photosynthesis and sending destruction up and down the food chain. Once the dust settled, greenhouse gases locked in the atmosphere would have caused the temperature to soar, a swift climate swing to topple much of the life that survived the prolonged darkness.
Asteroid or Volcanoes?
The extraterrestrial impact theory stems from the discovery that a layer of rock dated precisely to the extinction event is rich in the metal iridium. This layer is found all over the world, on land and in the oceans. Iridium is rare on Earth but it's found in meteorites at the same concentration as in this layer. This led scientists to postulate that the iridium was scattered worldwide when a comet or asteroid struck somewhere on Earth and then vaporized. A 110-mile-wide (180-kilometer-wide) crater carved out of Mexico's Yucatán Peninsula, called Chicxulub, has since been found and dated to 65 million years ago. Many scientists believe the fallout from the impact killed the dinosaurs.
But Earth's core is also rich in iridium, and the core is the source of magma that some scientists say spewed out in vast, floodlike flows that piled up more than 1.5 miles (2.4 kilometers) thick over 1 million square miles (2.6 million square kilometers) of India. This bout of volcanism has also been dated to about 65 million years ago and would have spread the iridium around the world, along with sunlight-blocking dust and soot and greenhouse gases.
Both hypotheses have merit. Some scientists think both may have contributed to the extinction, and others suggest the real cause was a more gradual shift in climate and changing sea levels. Regardless of what caused the extinction, it marked the end of Tyrannosaurus rex's reign of terror and opened the door for mammals to rapidly diversify and evolve into newly opened niches.
What caused this mass extinction that marks the end of the Cretaceous and the beginning of the Paleogene? Scientists have yet to find an answer. The one that does must explain why these animals died while most mammals, turtles, crocodiles, salamanders, and frogs survived. Birds escaped. So did snails, bivalves, sea stars (starfish), and sea urchins. Even hardy plants able to weather climate extremes fared OK.
Scientists tend to huddle around one of two hypotheses that may explain the Cretaceous extinction: an extraterrestrial impact, such as an asteroid or comet, or a massive bout of volcanism. Either scenario would have choked the skies with debris that starved the Earth of the sun's energy, throwing a wrench in photosynthesis and sending destruction up and down the food chain. Once the dust settled, greenhouse gases locked in the atmosphere would have caused the temperature to soar, a swift climate swing to topple much of the life that survived the prolonged darkness.
Asteroid or Volcanoes?
The extraterrestrial impact theory stems from the discovery that a layer of rock dated precisely to the extinction event is rich in the metal iridium. This layer is found all over the world, on land and in the oceans. Iridium is rare on Earth but it's found in meteorites at the same concentration as in this layer. This led scientists to postulate that the iridium was scattered worldwide when a comet or asteroid struck somewhere on Earth and then vaporized. A 110-mile-wide (180-kilometer-wide) crater carved out of Mexico's Yucatán Peninsula, called Chicxulub, has since been found and dated to 65 million years ago. Many scientists believe the fallout from the impact killed the dinosaurs.
But Earth's core is also rich in iridium, and the core is the source of magma that some scientists say spewed out in vast, floodlike flows that piled up more than 1.5 miles (2.4 kilometers) thick over 1 million square miles (2.6 million square kilometers) of India. This bout of volcanism has also been dated to about 65 million years ago and would have spread the iridium around the world, along with sunlight-blocking dust and soot and greenhouse gases.
Both hypotheses have merit. Some scientists think both may have contributed to the extinction, and others suggest the real cause was a more gradual shift in climate and changing sea levels. Regardless of what caused the extinction, it marked the end of Tyrannosaurus rex's reign of terror and opened the door for mammals to rapidly diversify and evolve into newly opened niches.
Category
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AnimalsTranscript
00:00Our planet has been struck by a series of disasters that wiped out 99% of all species
00:11that ever lived.
00:13But if it hadn't been for these catastrophes, none of us would be here at all.
00:24Sixty-five million years ago, an asteroid the size of Everest smashed into the Earth
00:29at 60 times the speed of sound.
00:34It triggered one of the greatest mass extinctions the planet had ever seen, and the death of
00:40the dinosaurs.
00:43This is the story of that great impact.
01:04Our planet is around 4.5 billion years old, and a lot has happened in that time.
01:13It's tough getting a handle on such an enormous period.
01:17So to put it in perspective, imagine the whole of Earth's violent history compressed into
01:22a single day, represented by a clock.
01:27At midnight, the planet formed.
01:34At 1138 in the evening, the Earth suffered a catastrophic cosmic impact, a strike so
01:42large it blasted billions of tons of debris into space and set the whole planet on fire.
01:50It triggered a chain of events that wiped out 70% of all life on Earth, including the
01:56dinosaurs.
01:59It was an event that changed the course of evolution and led directly to the emergence
02:04of mammals and eventually humans.
02:08But how do we know what happened?
02:10For many years, scientists pieced together a series of clues from around the world to
02:15build a detailed picture of the day the dinosaurs died.
02:28This is the Red Deer River Valley in the Canadian Badlands.
02:35Here paleontologist Phil Currie hunts for clues to one of the most violent chapters
02:41in Earth's history, the last great mass extinction.
02:49Currie searches for the fossilized remains of the last of the dinosaurs, buried within
02:55the valley rocks.
02:58The wonderful thing about these badlands is you can go almost anywhere, and at specific
03:05levels you can actually find bone in great abundance.
03:09This was picked up in less than 10 minutes, and we have things like whole claws, sometimes
03:14whole teeth.
03:16Basically along the Red Deer River we have 10 million years of dinosaurian history represented.
03:24And at each level there are different dinosaurs.
03:31These layers of rock represent millions of years of evolution.
03:37The deeper the layer, the further back it is in time.
03:41Well, as you can see, the rock here is actually in layers.
03:47We have a layer of sandstone here, a layer of mudstone below it, layers of coal, layers
03:53of siltstone, layers of different things, but they're all laid down horizontally, one
03:58on top of the other.
04:00In a way it's kind of like looking at a book from the back forwards.
04:04Each one of these pages, of course, represents a different page in the history of the Earth.
04:12Somewhere in these layers lie clues to the death of the dinosaurs.
04:19Several feet below the surface is a layer that's intrigued scientists for generations,
04:24the Cretaceous Tertiary, or K-T boundary.
04:29This is exactly what I was looking for.
04:31This is where we have the Cretaceous Tertiary boundary, and this is the area that for a
04:37long time we suspected would tell us something about the extinction of dinosaurs, because
04:43below the layer we have dinosaurs, and above the layer we have no evidence of dinosaurs
04:48at all.
04:50The layer dates to the same time period as the mass extinction that wiped out 70 percent
04:55of all life on Earth.
04:59So this appears to be the smoking gut.
05:02This may be the layer that indicated that there was a catastrophe 65 million years ago.
05:10The K-T boundary extends far beyond the Canadian Badlands.
05:15Scientists have found this same layer all over the world.
05:19Below it, fossils from countless species.
05:22Above it, 70 percent of them are gone, including the dinosaurs.
05:28Nobody knew what caused this mass extermination until clues emerged 5,000 miles away, in
05:35southern Europe, Zumaia Beach, northern Spain.
05:48Hidden within these spectacular cliffs is evidence of what scientists believe wiped
05:53the dinosaurs off the face of the Earth.
05:59Almost 30 years ago, biologist Jan Schmidt came to these very cliffs.
06:07He was investigating what wiped out the dinosaurs, and was one of the first to think the K-T
06:13boundary layer might hold the answer.
06:15I started to analyze the rocks chemically, approaching the K-T boundary right there,
06:21because I thought there must be something hidden in the rocks to tell the story how
06:25they got extinct, why they disappeared.
06:28What he discovered shocked the scientific world.
06:33The samples contained an extremely rare metal, iridium.
06:40That is, it's rare in rocks on Earth.
06:44Most of the Earth's iridium is trapped 4,000 miles below ground in the planet's core.
06:51But it is found in meteorites and asteroids.
06:55And when you find a high abundance of iridium, you know you have a clue to extraterrestrial
06:59material.
07:00It has to come from outer space, rather than from the surface of the Earth.
07:05There was only one conclusion.
07:08A very big object must have hit the Earth.
07:16The iridium suggested that 65 million years ago, a massive asteroid hit the planet, at
07:23the exact same time as the death of the dinosaurs.
07:27Many scientists were now convinced they had the murder weapon, a catastrophic asteroid
07:33strike.
07:37But to prove it, they needed to find the crime scene, the site of the impact.
07:46So scientists began a global search for an impact crater.
07:52By measuring the worldwide spread of iridium, they estimated that the crater must have been
07:56enormous, around 125 miles in diameter.
08:04The problem with iridium is, it's within the meteorite, but the meteorite is totally vaporized,
08:10and the iridium is strewn out over the whole world.
08:12It doesn't matter whether you're here or there on the surface of the planet, you find the
08:16same amount of iridium.
08:17So it doesn't tell you where to look for it.
08:21The scientists knew there had been an impact, and they knew it was big.
08:29But finding it was tough, because millions of years of erosion had wiped away the evidence
08:34of the impact site.
08:37It would take a combination of luck and sheer perseverance to find the dino-killer.
08:4311.38 p.m. on our clock of the Earth's history, 65 million years ago, 70 percent of all life
08:57on the planet has been wiped out, including the dinosaurs.
09:02Scientists thought this could have been the result of a cataclysmic asteroid impact, but
09:07they had no real evidence of an impact big enough to cause such mayhem.
09:12To prove it, and to build a picture of how the dinosaurs died, they needed to find the
09:16impact crater.
09:19Dan Derda is a NASA planetary scientist.
09:23He specializes in the aftermath of massive cosmic impacts.
09:29And where better to come than here?
09:33One of the world's most spectacular asteroid craters.
09:41Meteor Crater, Arizona.
09:44The impact that created it happened just 50,000 years ago.
09:48The asteroid that struck here was only 150 feet across, yet it created a crater three
09:54quarters of a mile wide, and devastated an area the size of Los Angeles.
10:02The crater is many times smaller than the crater that would have been left by the KT
10:07asteroid.
10:08But it demonstrates the enormous power of even a relatively small asteroid strike.
10:15If a meteorite the size of a large house could make a crater of this size, imagine the devastation
10:20wrought by the impact of an asteroid the size of Mount Everest.
10:23That's the scale of the KT impact.
10:29Meteor Crater is a key clue in the search for the KT strike, because buried in its walls
10:36is evidence of how cosmic impacts transform stone.
10:41That immense impact released in energy, our modern estimates are something on the order
10:45of one to ten megatons.
10:47That's the scale of the largest nuclear devices we've ever detonated.
10:51That immense impact excavated millions of tons of rock.
10:55It peeled open the desert like the petals of an immense flower, and sprayed blocks of
11:01ejecta, huge masses of rock the size of a small house, for miles in every direction
11:07out into the desert.
11:12The heat and trauma of the impact was enough to transform rock itself, shocking and pulverizing
11:19individual mineral grains.
11:24One sign of the violence of an impact event like this can be found in the rocks themselves.
11:29This is Coconino sandstone.
11:30It's a pretty solid sandstone.
11:32It's made out of quartz grains that have been cemented together.
11:36When this rock was shocked in the impact itself, it was pulverized and broke those sand grains
11:44down into a much finer material, almost the consistency of flour.
11:48You can see here what the impact has done to that material, which has now been cemented
11:52back together in the walls of the crater.
11:56Very violent event that can turn rock into flour.
12:00This dramatic transformation was a vital clue in the search for the location of the asteroid
12:05strike.
12:07It pointed the scientists in the right direction.
12:14Following the trail, Dan Derda flies north to Trinidad, Colorado.
12:24He examines levels of minerals in the K-T boundary line.
12:30The layer contains tiny mineral crystals similar to the ones at Meteor Crater, as small as
12:37grains of salt.
12:41It's quartz, but that's not why it's interesting.
12:45It's interesting because something smashed it to pieces.
12:50So here in the K-T boundary layer, this thin white clay layer deposited, we find evidence
12:58not only of the iridium, which was the original signature that something funny, something
13:02extraterrestrial is going on here.
13:04This is that layer where we also find the shocked quartz.
13:11Shocked quartz is created when quartz is smashed by an extreme force at speeds exceeding thousands
13:16of miles an hour.
13:24Only one natural phenomenon packs enough punch to shock quartz, an asteroid impact.
13:35These tiny grains seem to confirm that the asteroid that hit the Earth was colossal,
13:40and the impact took place around the time of the dinosaur extinction.
13:46But the quartz grains also took scientists a step closer to the impact site.
13:51While the iridium was spread evenly around the boundary layer, the shocked quartz was
13:56not.
13:58As we look at the thickness of this layer, here in Colorado it's about a half an inch
14:02thick or so.
14:03As we move to the southeast, however, that layer gets thicker and thicker.
14:07It grows into meters thick as we move toward the southeast, toward the Caribbean.
14:12And so the increasing amount of shocked quartz and the thickening of that layer as we move
14:16to the southeast, toward the Caribbean, is probably a pretty good indication that the
14:21impact occurred in that region of the world.
14:27The shocked quartz pointed to an impact somewhere in the Caribbean.
14:32Still, the scientists couldn't find the crater.
14:38Then researchers got a lucky break.
14:46In 1978, Pemex, the Mexican oil company, was surveying the Yucatan Peninsula.
14:54Geophysical data from the survey and gravity field maps revealed a giant horseshoe-shaped
14:59structure buried three-quarters of a mile underground beneath the sea off the Mexican
15:05coast.
15:08It was huge, 112 miles across, 12 miles deep, with outer impact rings stretching to 125
15:17miles in diameter.
15:20You see circles around each other like a bull's eye.
15:24And the rings define the size of a crater.
15:26And it turns out that the largest ring was around 200 kilometers in size.
15:31And that was exactly the size of the crater which was predicted 10 years before.
15:37It was massive, it was old, and it had all the signs of an impact crater.
15:44They took samples during drilling, and later on the microscope we found shocked quartz.
15:49By analysis of the rocks, we found high abundance of iridium.
15:54The iridium and shocked quartz in the crater matched samples from the K-T boundary layer.
16:01Scientists were convinced they had found the impact crater.
16:06But to be sure, they wanted physical evidence at the surface.
16:11They got their break inside a Mayan human sacrificial pit in tropical Mexico.
16:2011.38 p.m., on our clock of Earth's history, 65 million years ago, 70 percent of all species
16:32on Earth, including the dinosaurs, were wiped out.
16:38Scientists believe the cause was a catastrophic asteroid impact.
16:44They'd unearthed evidence of a massive crater in Mexico's Yucatan Peninsula,
16:50buried off the coast, deep underground.
16:58What the scientists wanted was real physical evidence at the surface to prove that this
17:03really was the site of the K-T impact.
17:08Chichen Itza in Mexico.
17:14The Mayans worshipped here a thousand years ago, but the land they built on was shaped
17:19by an event 65 million years earlier.
17:26The area is famous for its Mayan temples, and also for its cenotes, or sinkholes.
17:36They form when limestone rocks get hollowed out by water, forming caves.
17:45As the cave gets bigger, its roof weakens.
17:48Finally, it collapses, leaving an open cenote.
17:56To the Mayans, they were sacrificial pools.
18:02To us, they are pointers to a species-killing impact crater.
18:08In 1996, NASA scientist Adriana Ocampo made the connection between the cenotes and the
18:15impact.
18:17She realized that the pattern of the cenotes across the region was physical evidence of
18:23the crater.
18:24The discovery really was like a detective story.
18:28The cenote ring was the last piece of the puzzle that gave credence to the theory.
18:41Cenotes normally occur along lines of weakness or faults in the bedrock.
18:49Ocampo realized that the Yucatan cenotes may not be on natural fault lines.
18:55The faults could have come from an impact.
19:01She studied satellite images of the Yucatan Peninsula, and compared them with the oil
19:06company's maps.
19:10The cenotes were arranged in a semicircular ring, exactly matching that of the impact
19:16crater.
19:18Here we are at the ring of the Cretaceous Tertiary Impact Crater.
19:26This cenote is one of many hundreds of cenotes that form a semicircle that is the surface
19:34evidence of the Cretaceous Tertiary Impact Crater.
19:39If we were a satellite looking down on Earth, then we would be able to see the ring of the
19:46cenotes.
19:49The ring of cenotes confirmed the impact's immense size.
19:55You truly need to have that satellite perspective to be able to really get the dimension.
20:03It really truly is one of the largest impact craters on our planet.
20:08The pattern of cenotes was the final clue in the hunt for the K-T impact event.
20:15Finally, scientists had the exact location of the impact.
20:20They could begin to build up a detailed picture of the day the asteroid struck.
20:29Sixty-five million years ago, a giant lump of rock hurtled through the solar system at
20:3845,000 miles an hour.
20:42It was six miles wide and weighed about a trillion tons, the size of Mount Everest.
20:51And it was on a collision course with Earth.
20:55It smashed through the atmosphere and crashed into shallow seas at twenty times the speed
21:01of a bullet.
21:32The impact released six million times more energy than the 1980 eruption of Mount St.
21:38Helens.
21:51It set off a trail of destruction that would end with the death of the dinosaurs.
21:59And you realize that at that size, when that asteroid impacted the Earth, at the moment
22:04it started to contact the surface of the Earth, its trailing edge was still up there at 35,000
22:10feet.
22:11That's the altitude that jetliners are flying.
22:13So we're really talking a massive object slamming into the Earth.
22:21In the history of the Earth, only one other impact was larger.
22:26The collision with the proto-planet Theia, 4.3 billion years before.
22:33This collision created our Moon.
22:41The KT impact was not nearly as large, but its effects wiped out roughly 70% of life
22:47on the planet.
22:52The initial plume of superheated gases and debris incinerated virtually all life in the
22:57impact zone.
23:00Nothing within a thousand mile radius stood a chance.
23:05It literally would have been hell on Earth.
23:06This mountain of rock would have immediately, the contact point would have started glowing
23:11with a brilliance like the surface of the sun.
23:15You probably, just from the heat of the fireball itself coming in, the flesh would have been
23:21burned off your body just from the intensity of that fireball itself.
23:31To understand what happened on the day of annihilation, scientists recreated in the
23:36lab NASA's Ames Research Center, just outside San Francisco.
23:47NASA scientist and asteroid strike expert Peter Schultz recreates the moment of impact
23:53when an asteroid hits shallow seas, just as it did 65 million years ago.
24:03First he builds a layer of sand to represent the land.
24:07Then he covers it with water to simulate the ancient ocean.
24:12What we're trying to do is to put an ocean in here.
24:15We're trying to cover up the land with a shallow ocean.
24:20So this is kind of like something comparable to the impact on the Yucatan 65 million years
24:26ago.
24:29To simulate the asteroid impact, he uses the Ames vertical gun.
24:36It can fire a projectile at 18,000 miles an hour.
24:41We should probably be able to see everything coming in, exploding, and then moving down
24:47range.
24:48So that should be good.
25:00Schultz raises the barrel of the gun to recreate the most probable angle of impact.
25:07He then loads the projectile, a steel ball, to represent the asteroid.
25:34It's vital to examine the impact in detail, but the scale-down event happens too fast
25:39for the naked eye.
25:42So Schultz records the impact using ultra-high-speed photography.
25:56That is simply extraordinary.
25:58Look at that.
26:06Okay let's see what really happened.
26:09Step through this slowly.
26:11Oh!
26:12Let me go back.
26:13Look at this.
26:14Oh this is gorgeous.
26:15Kapow!
26:16Now it came in this direction, slammed in.
26:20This is now vapor that is expanding, heating up the atmosphere, just turning it into fiery
26:26hot.
26:27Almost as hot as the surface of the sun.
26:29It's really intense.
26:30This is the part that would have been lasting seconds, and then would have translated all
26:35the way down range, and then the crater began to form.
26:40The effect of the impact amazes even Schultz.
26:44If we imagine this being the Earth, our atmosphere, or if we were imagining ourselves in a jet
26:50plane 65 million years ago, we'd be flying along, and we would be only about less than
26:56my fingernail height.
26:59The simulation shows the pattern of debris ejected from the sand and water.
27:05The bullet throws up pounds of debris.
27:09Sixty-five million years ago, the asteroid would have kicked up billions of tons.
27:16We're talking about 500 billion tons of debris that was tossed out.
27:21We saw in the experiment that these were small splatters, but imagine this being the
27:27size of buildings, larger than buildings, the size of a small city.
27:32The material thrown up from the crater reached speeds of up to 25,000 miles an hour.
27:39Some of the debris would have actually achieved escape speed.
27:42It would have gone faster than the Earth could hold it together, to hold it in its orbit.
27:48That material could have made it to the moon.
27:51There may be some material sent from the Earth to the moon.
27:58The immediate effects of the impact were devastating.
28:03At the point of impact, the temperature hit 16,000 degrees Fahrenheit.
28:11It melted surrounding rocks and sent molten bullets flying out at supersonic speeds.
28:19Then came a violent and powerful shockwave.
28:25Superheated 2,000 mile an hour winds hurtled out from the impact site, incinerating everything
28:32in their path.
28:35Hell came to Earth, and its creatures had no place to run.
28:43This is not, this is worse than a horror movie.
28:46This is worse than your worst dream.
28:48It's very difficult to contain our imagination when it comes to thinking about something
28:54this scale.
28:58The initial impact was over, but the aftermath was just beginning.
29:05The asteroid landed in water, triggering a gigantic tidal wave, one of the largest the
29:12Earth has ever seen.
29:19Sixty-five million years ago, a gigantic asteroid smashed into the planet.
29:30The impact shot out a superheated blast wave that reduced anything in the kill zone to
29:36ashes.
29:43But this was just the beginning.
29:46The asteroid landed in the sea, generating a huge tsunami.
29:54Peter Schultz's recreation shows in miniature what he thinks happened next.
30:01The shockwave from the impact itself actually causes the water to splash out.
30:08So we've already created a shock that is the beginning of a tsunami that would have traveled
30:14all the way across the Gulf of Mexico.
30:16It would have been speeding along and then crashing on the shores in Alabama, Georgia,
30:22that whole region, and over on the western side of Mexico.
30:30The tsunami of 2004 was around 30 feet high.
30:40The tsunami 65 million years ago would have been 10 times higher and thousands of times
30:46more destructive.
30:53A 300-foot wall of water hurtled out from the impact zone at hundreds of miles an hour.
31:02First a superheated fireball, then a blast wave, then a mega-tsunami.
31:16Nothing within the kill zone could have survived the onslaught.
31:21Yet far from the impact radius, literally on the other side of the earth, dinosaurs
31:27were wiped out.
31:30Nothing didn't add up, unless the aftermath of the impact was even greater than thought.
31:38Back at the K-T boundary in Colorado, planetary scientist Dan Derda has unearthed a microscopic
31:44clue that could explain how the impact triggered a global catastrophe.
31:49In addition to the iridium that we see in this layer and the shocked quartz grains,
31:53we find small particles of soot, in some cases actual charcoal.
31:57The soot we certainly see all across the layer and in all parts of the world.
32:01And in fact, if you add up the total amount of soot in that boundary layer, it adds up
32:06to something spread globally.
32:07It's something on the order of 70 billion tons of soot.
32:13That's roughly equivalent to, you know, all the earth's vegetation going up in flames
32:17at once.
32:21This layer of soot found in the K-T boundary throughout the world can mean only one thing.
32:27A global inferno.
32:32But just how does a whole planet catch fire?
32:43Los Alamos, New Mexico.
32:48It's the birthplace of the atomic bomb, but today Los Alamos scientist Kathy Plesko studies
32:54a much larger explosion.
32:58Here at the Applied Physics Division, Plesko and the team use supercomputers to study how
33:03a cosmic impact could incinerate an entire planet.
33:10The simulation also reveals for the first time just how the planet burst into flames.
33:20The impact was so powerful, it hurled over 500 billion tons of debris into the air.
33:27A lot of it makes it up into the upper atmosphere and some of it even makes it out of the atmosphere
33:32and it orbits in space for a little bit and then re-impacts into the surface of the earth
33:38somewhere else.
33:39So this debris actually went all over the surface of the earth and as it was coming
33:43back in, just like when you see in a meteor shower things heat up as they come back in
33:48to earth's atmosphere, this debris would have heated up too.
33:51But there was so much of it that it would have heated up the entire atmosphere and started
33:56forest fires just from spontaneous combustion on the opposite side of the globe.
34:03For hours after the impact, billions of tons of superheated debris rained down on earth.
34:10It buried the planet in burning rock and set the earth on fire.
34:19Soon most of the world was ablaze.
34:23Many animals far from the impact zone survived the initial blast, only to die in the raging
34:30wildfires.
34:36For the dinosaurs, anywhere on the planet would have been lethal.
34:41At that point, anything standing anywhere on the surface of the planet, even in Antarctica
34:45or Siberia on the other side of the world, would have been in real trouble.
34:50It was a very, very bad day for the dinosaurs.
34:55Incredibly, against all the odds, a few dinosaurs did find shelter and survived the tsunami
35:00and the global fires.
35:04But even their days were numbered.
35:07Of all the places on the planet the asteroid could have struck, it hit the worst possible
35:13spot.
35:161138 p.m. on the clock of earth's history, 65 million years ago, a massive asteroid struck
35:27off the Mexican coast.
35:30The impact, the tsunami, and global wildfires that followed wiped out almost every living
35:36thing on the planet.
35:44A few hardy creatures still survived, but they faced an even greater threat, sudden
35:51and dramatic climate change.
35:57The impact lofted all of this ash and debris and dust into the atmosphere, blanketing the
36:02entire atmosphere with a thick, opaque layer that made it night for about two to six months.
36:09You couldn't see anything.
36:10You couldn't have seen your hand in front of your face on the other side of the world
36:13for six months.
36:16If you were sitting on the moon watching this, it would have been your worst science fiction
36:21movie.
36:22It would have been a very, very different place.
36:25Not the blue planet.
36:26It would have probably been more of a gray planet.
36:33Dust and ash blocked out the sun.
36:38Temperatures dropped like a stone and kept on dropping, thanks to the impact's location.
36:47If there was one place on earth that would have been a bad place to be hit, it was Yucatan
36:51Peninsula.
36:53The fact is that that area had a lot of sulfur bearing minerals, and that has longer term
36:59effects on the global climate, as well as immediate poisoning in the area around it.
37:07The blast generated incredible heat.
37:10It vaporized the rock and blasted tons of sulfur dioxide into the air.
37:19The gas mixed with water in the atmosphere to form droplets of sulfuric acid.
37:25And that was a disaster.
37:29The droplets were highly reflective.
37:32They bounced the sun's heat energy away from the earth and sent temperatures plummeting.
37:42So at first, you have the dust lofted into the atmosphere, which blocks out the sun.
37:47That eventually falls back as the atmosphere convects and cleans itself out.
37:51But then you've still got these sulfur oxides up in the upper atmosphere, which reflect
37:55sunlight and cool the planet.
37:57So this prolonged the impact winter for probably another couple of years.
38:06Temperatures dropped by about 10 degrees Fahrenheit.
38:11Forests destroyed by the global fires struggled to regenerate.
38:17Eventually the sulfur dioxide fell to earth and temperatures returned to normal.
38:24But there was a sting in the tail.
38:26The sulfur dioxide fell as acid rain.
38:32First you have this six month long winter where there's no sunlight at all.
38:37And then finally you get a little bit of sunlight and the plants think, oh good, finally I can
38:41sprout my seeds and grow again.
38:43And then the sulfur dioxide falls as acid rain and burns all the leaves off your plants.
38:50The food chain collapsed.
38:56The few animals that had survived the blast, the tsunami, the raging fires and the plummeting
39:02temperatures now began to starve.
39:08And the asteroid's after effects just kept on coming.
39:13Now global cooling made way for global warming.
39:21The rocks the asteroid hit didn't just contain sulfur.
39:25They also contained carbon dioxide.
39:32Vaporized by the impact, the rocks released billions of tons of greenhouse gases.
39:38The equivalent of 3,000 years of modern fossil fuel burning.
39:43The carbon dioxide was the last effect of the impact and it hung on for centuries now
39:50warming the planet instead of cooling it.
39:53So the climate is then artificially warm and not returning to normal values for several
39:59centuries after the impact.
40:02The effects of excess carbon dioxide were devastating.
40:08Temperatures increased by about 20 degrees over the next 100 years.
40:12It was global warming on a fast track.
40:16It was a true ecosystem collapse, something that we can't even imagine at any scale today.
40:22And there was no recovery.
40:23It wasn't a bad summer.
40:24It was a devastating hundreds of years.
40:31Temperatures soared.
40:35Much of the land turned to parched deserts.
40:39Vegetation died.
40:45Plant-eating dinosaurs starved to death.
40:49Now the carnivores had nothing to eat.
40:52They died too.
40:55After 150 million years of supremacy, the reign of the dinosaurs came to an end.
41:02They were goners.
41:04They were great to live on Earth at that time.
41:06They ruled the Earth, but they couldn't defend themselves against the big one.
41:11And now here we are, the supreme species on the planet.
41:16Could we survive an impact the size of the KT strike?
41:21If something as big as the KT impact occurred now, only a portion of the world would survive.
41:28Most of North America would be wiped out, and the debris coming back through the atmosphere
41:33still would have affected them.
41:36And then the longer-term effects of the sudden change in climate, maybe oscillating from
41:41something that would be incredibly warm to incredibly cold, would have been very difficult
41:45to adjust.
41:48It would have been a long time of survival.
41:51But could it happen again, or was it a one-off?
41:55Of course, it will happen again.
41:58And this is nature.
41:59This is what happens.
42:00We get hit now and then, and something that's as big as the KT impact should happen every
42:06hundred million years or so.
42:10The bigger the impact, the rarer it is.
42:13So we could be waiting another 35 million years for another dinosaur killer.
42:19But smaller impacts are much more frequent.
42:27Fifty thousand years ago, a 150-foot asteroid created the Meteor Crater in Arizona.
42:35That one devastated an area the size of Los Angeles.
42:42As recently as 1908, the Tunguska asteroid destroyed an area of 830 square miles.
42:50Impacts this big happen around every 100 years or so.
42:54So we're due another one very soon.
43:02The KT impact wiped out 70% of all species on Earth.
43:09But despite the death and destruction, life persisted, somehow.
43:15A few species not only survived, they thrived, and eventually evolved into us.
43:25Sixty-five million years ago, a giant asteroid hit the Earth.
43:30It set off a chain of events that wiped out 70% of life on Earth, including the dinosaurs.
43:45But with the dinosaurs gone, a new species of animal, the mammal, took center stage.
43:53These highly adaptive creatures were small in size, but eventually they would dominate
43:59the planet.
44:00One branch would evolve into humans.
44:04The extinction of the dinosaurs clearly cleared the way, if you will, emptied the world of
44:09that particular ecological niche, and gave the mammals a chance to rise to prominence.
44:14And so the extinction of the dinosaurs was sort of the crucible of human evolution, ultimately,
44:20if you will.
44:21We're here because they're not.
44:26But why did these primitive mammals survive when so many other species didn't?
44:31The answer lies in Golden, Colorado.
44:35Here J. Lynn Eberle hunts for the remains of our direct ancestors.
44:41In a layer just above the KT boundary, she's found the fossilized bones of animals that
44:46survived the impact, the fireball, and extreme climate change.
44:53They were small mammals, the size of rodents.
44:57They seem unlikely heirs to the dinosaurs' crown.
45:01But the qualities that had once kept them near the bottom of the food chain now took
45:05them to the top, starting with their small size.
45:09If we compare the KT meteorite impact to, say, something we can envision today, such
45:15as a nuclear war, the organisms that would be most likely to survive something like that
45:21are going to be the small ones, the ones that can escape the surface in some way through
45:26burrowing, living underground.
45:28They had a much higher chance of surviving than anything that would be on the surface,
45:32such as these large dinosaurs.
45:36And these subterranean survivalists had another thing in their favor.
45:41They were omnivores.
45:43They would eat just about anything.
45:47The mammals that you have right after the KT impact, such as this fellow right here
45:51by a conodon, these guys are generalists, meaning they could probably eat a variety
45:56of different things.
45:57For mammals, being a generalist would be very helpful after the KT boundary, because there
46:03are going to be a variety of foods on the scene.
46:07And I think if you were too specialized, the KT boundary might have been where you met
46:14your end.
46:17Mammals had another significant survival advantage.
46:22Unlike the dinosaurs, they didn't lay their eggs on the ground or raise their young out
46:27in the open, where the predators lurked.
46:32Dinosaurs lay eggs and their young develop in eggs and then hatch.
46:37Mammals on the other hand, they lay their eggs on the inside, if you will, and their
46:42young develop on the inside with that added protection of the mother, the mother's body.
46:48That probably was advantageous right after the KT boundary, because those young just
46:53had further protection from the environments, the elements, predators, scavengers.
47:00A few egg layers did make it.
47:03Some were the flying dinosaurs who laid their eggs in trees.
47:08They evolved into birds.
47:12And the primitive reptiles survived, like crocodiles that buried their eggs underground.
47:18Along with the mammals, these survivors of the catastrophe flourished.
47:25It was the meek, the burrowers and scavengers who inherited the earth.
47:32And eventually they evolved into us.