How the Universe Works - S10E04 - Dark History of Earth
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00:00The Earth is over 4.5 billion years old.
00:05Its history is shaped by disaster
00:10after disaster.
00:14Asteroid and comet collisions,
00:16flares from the sun,
00:18mass extinctions,
00:20supernova explosions,
00:22cosmic ray bombardment.
00:24You name it, we've experienced it.
00:26It's kind of a miracle we're here at all.
00:30These violent events could be why Earth has life.
00:35We tend to think of disaster as a bad thing,
00:38but out of chaos can come possibility.
00:41When we destroy something,
00:43we can also create something new.
00:47Earth has walked the line between survival
00:51and destruction.
00:53It's tipping that fine balance of luck
00:55between a good disaster and a bad disaster.
00:58Could catastrophe and chaos
01:00be the essential ingredients for life?
01:042021.
01:23Scientists investigate something mysterious
01:26buried deep inside the Earth.
01:29It's a long-hidden clue to our violent past.
01:34Deep down 1,800 miles below the surface of the Earth,
01:38our core is surrounded by fluid rock,
01:41but inside that, 600 miles high
01:44and thousands of miles across
01:46are two denser regions,
01:48and they kind of cup the core of our planet like two hands.
01:52One of them is half the size of Australia, for crying out loud,
01:56so there are big lumps down there.
01:58There's a reason they should be there.
02:00It's a mystery to us.
02:03To solve this mystery,
02:05scientists need to examine the rocks
02:07buried over 1,000 miles beneath the surface.
02:12We don't really know what these two big rocks are made of
02:15sitting there on the core.
02:17However, we've been able to sample them.
02:19How in the world is that possible?
02:21Well, these blobs are actually feeding mantle plumes
02:24that are rising up through the mantle.
02:27So volcanoes in Iceland and Samoa, for instance,
02:30will dredge up some of these lumps of rock from the mantle.
02:34It's a precious chance for us to sample some of that deep rock
02:37that we'd normally not get a chance to see.
02:42These rocks are old, very old.
02:46It turns out that the samples in the lava
02:48that we think came from these blobs of rock in the mantle
02:51are 4.5 billion years old.
02:54This rock is as old as the age of the Earth.
02:58So they tell us something about, you know,
03:00how the internal structure of our planet
03:02was arranged in the earliest days of the formation of our planet.
03:06So getting samples from that time is very, very important.
03:09The age of the rocks may be a clue to their origin.
03:13They date back to a time of monstrous cosmic mayhem.
03:194.5 billion years ago,
03:21the solar system was still a pretty wild place.
03:25We're approaching the end of the formation of planets.
03:28Earth would still be growing.
03:32Back then, you wouldn't necessarily recognize the Earth.
03:36In fact, you wouldn't recognize the Earth at all.
03:39For example, no moon.
03:41The Earth did not have a moon when it first formed.
03:44The young Earth orbits the sun with other infant planets.
03:49One of them is an object scientists call Theia.
03:55And it's on a collision course with our home.
04:05The Theia collision would have been a spectacular event.
04:08It would have been one of the coolest things
04:10you could possibly witness in the origin of the solar system.
04:13Certainly the biggest event in the history of the Earth.
04:20The Theia event is something that completely reshaped the Earth.
04:25The planet that the Earth was before the Theia event is gone forever.
04:31The impact melts rock and throws out over a billion, billion tons of debris.
04:38During this incredible collision,
04:42these two planets were literally broken apart
04:45and combined into one big planet.
04:47Huge chunks of Theia stayed together
04:50as the now molten Earth began to form anew.
04:54Now we can kind of paint a picture of where these big lumps of rock might have come from.
04:58They're very old.
04:59They're in fact the same age as that large impact event.
05:04They could be pieces of Theia.
05:07The giant slabs of Theia sink down into our planet
05:13and lie undiscovered for billions of years.
05:22Earth reforms from the ruins of both planets.
05:27Now you might think that a collision like this is just devastating.
05:31There's no upside at all.
05:33But there are some things that came out of this collision
05:35that may have led to the possibility of life.
05:40When these two planets combine,
05:42parts of Theia's iron core merge with Earth's.
05:47So that means that Earth collected a much bigger core
05:50than it might have possessed on its own.
05:52This is good news for us because the core
05:54is the source of the magnetic field that protects us.
05:57Liquid metal flowing around in the outer core
06:00generates Earth's magnetic field.
06:04A protective shield from the sun.
06:09The sun can actually output billions of tons of high energy protons and electrons
06:13in a single burp.
06:16That eventually would have stripped away our atmosphere.
06:19If it weren't for that active core in that magnetic field,
06:22we would look like Mars, just sort of a bare and barren desert.
06:26Thanks to Theia's extra iron, Earth's molten outer core is large.
06:33So it cools slowly, staying molten,
06:37and keeps on generating a strong magnetic shield.
06:43Because of that collision, the extra iron, the extra heat,
06:46we've stayed active.
06:48We have a magnetic field. We are protected.
06:51And in fact, that's why we're here talking about it.
06:55The catastrophic impact helped life in other ways.
06:59The Theia event was absolutely huge.
07:01Not an impact like a 100-mile asteroid making a big crater in the desert,
07:05but a planet hitting a planet,
07:08causing a huge disk of debris spread out from the Earth,
07:12out of which formed the moon.
07:19After the collision, the Earth tilts on its side
07:23and spins incredibly fast.
07:27A day only lasts a few hours.
07:32The Earth itself rotates slightly on its side,
07:36and if left to its own devices,
07:39would in fact experience unpredictable chaotic wobbling.
07:44The fact that the moon is there stabilizes the Earth,
07:48stabilizes our climate.
07:52The moon's gravitational pull on our oceans
07:55creates tides and slows down the Earth's spin,
08:00creating a world primed for life.
08:04We actually owe quite a bit to the moon and Theia, its progenitor,
08:09for making Earth a hospitable planet for life.
08:14A giant collision 4.5 billion years ago sounds like a catastrophe,
08:18but it was probably the best thing to happen to the Earth.
08:23Theia, I would shake your hand, because we have a lot to owe you.
08:29We also owe the science of chance,
08:33because we lucked out with a one in a million impact.
08:37If the impact from Theia had been a little bit harder,
08:40the Earth may not have recovered as well as it did,
08:43and we may not be here to talk about it right now.
08:46If it had been a little bit less forceful,
08:48then the impact of it may not have made the changes
08:51that I think were needed for us to be here now.
08:54We got lucky.
08:56Most planets don't get to survive a collision like that
08:59and get a bonus moon out of the deal.
09:04Earth's huge collision with Theia
09:07was not our planet's first brush with danger.
09:12An earlier explosive event could have stopped the solar system
09:16from sparking into life,
09:19and the Earth from forming.
09:35Supernovas are one of the universe's most destructive events,
09:41releasing in one second
09:44as much energy as our sun will in its entire lifetime.
09:50But rather than wipe us out,
09:53supernovas may have kick-started the solar system.
09:574.6 billion years ago, the solar system was not even really the solar system.
10:01It's the precursor of the solar system.
10:05So what we had was a cloud of gas and dust collapsing in on itself,
10:09forming the sun in the center,
10:12and a disk around it out of which all the planets were forming.
10:16There are all kinds of vast clouds of dust and gas floating around the galaxy.
10:21What actually causes them to start collapsing and forming new stars?
10:25Well, you have to give that cloud a push.
10:28Scientists think this push could be a stellar blast,
10:35a supernova.
10:38Supernovae are some of the most powerful events in the universe.
10:44One explosion can light up brighter than a galaxy.
10:50So not only do they eject elements and material,
10:53they also eject a lot of light and energy.
10:56A supernova explosion sends a shockwave racing out into space
11:01at 18,000 miles per second.
11:06The shockwave from a nearby supernova compresses material together
11:11until it begins to collapse under its own gravity.
11:17Was this how our solar system started?
11:21So far it's been really difficult to find evidence that there was some supernova
11:26or point to something that happened that really kick-started the solar system.
11:30The ancient supernova blast faded away a long time ago.
11:38Imagine a crime scene.
11:40Now imagine waiting 4.6 billion years after the crime is committed
11:45and looking at it and going, there's nothing here, what are we doing?
11:49That's kind of what we're trying to do here.
11:52Researchers from the University of Minnesota tried to solve this ancient crime
11:58by studying asteroids that fell to Earth as meteorites.
12:03Asteroids are critical for understanding the early solar system.
12:07And this is because they have frozen in place all the conditions that existed
12:11in that very early solar nebula right at 4.5 billion years ago.
12:17The asteroids contain information about the time leading up to the birth of the sun
12:22and the solar system.
12:26When a massive star ends its life as a supernova, it undergoes what we call nucleogenesis.
12:31In fact, we call it explosive nucleogenesis.
12:34Literally, the explosion is generating new types of nuclei, new elements, heavier elements.
12:41Well, it turns out the types of elements it makes depends on the star that blew up.
12:47The Minnesota team ran computer simulations to investigate which elements form
12:53when a star up to 12 times the mass of the sun explodes.
13:00Then they compared the results with analysis of elements found in asteroids
13:06dating back to the birth of the solar system.
13:10They match.
13:16So the remains of this supernova was actually under our noses all along
13:21in the elements that have been in our solar system for ages.
13:26And perhaps in the Earth as well.
13:30The Earth has lots of rocks that's made of silicon.
13:33That's only produced in supernova explosions.
13:36And the very core of our Earth, the thing that keeps us alive, that's iron, nickel.
13:41Again, you only get that in supernova explosions.
13:45In February 2021, scientists shed light on the supernova explosions
13:50that helped seed our solar system and provide the materials to build our planet.
13:58The researchers examined fragments blasted off the giant space rock Vesta
14:054.5 billion years ago and later landed on Earth.
14:10These asteroid fragments contain the fingerprints of not one,
14:14but at least two supernova explosions.
14:19Our solar system was seeded, was enriched by at least two separate supernova explosions.
14:25That's incredibly lucky because that is what delivers the ingredients necessary for life.
14:33Scientists believe that these two supernova explosions
14:37may have enriched different parts of the infant solar system.
14:41One provided the materials that helped form the outer gas planets.
14:48The other supernova seeded the inner solar system
14:52with elements that built the rocky planets, including the Earth.
15:00Once again, our fate came down to pure chance.
15:03A series of extraordinarily violent supernova blasts
15:07gave the solar system the kickstart it needed
15:10and the elements to build the planets without destroying our future home.
15:16It's a fine line between being too close to a supernova,
15:19which will just shred your prestellar cloud.
15:22And not too far away that you don't get any of the good stuff.
15:27Supernova, supernova, supernova.
15:31Supernova play both creation stories and destruction stories.
15:36They play both roles.
15:39We lucked out.
15:41This chapter of the story ends well.
15:44The solar system gets the ingredients it needs to build planets.
15:49Earth forms in a good location, close to its star.
15:55The future looks bright.
15:57But then, the biggest bombardment in history
16:01smashes into the Earth.
16:17From the moment our planet formed,
16:21we've been under fire.
16:272021, a fireball streaks across the night sky in Europe.
16:342018, a 1,500-ton meteor explodes over the Bering Sea
16:39with ten times the energy of an atomic bomb.
16:462013, an asteroid explodes over Russia, injuring over 1,000 people.
16:53The Earth is hit by quite a few asteroids every day.
16:56You see them as shooting stars, meteors in the sky.
17:00These events are violent and destructive,
17:03but these space invaders also brought something
17:07every living planet needs, volatiles.
17:11When we say volatiles, what we mean are elements
17:14that are really light and easily moved around.
17:16Often they're gases, so that's oxygen and water and carbon dioxide
17:21and just all those light elements that are really important building blocks for life.
17:25These elements are abundant on our planet today,
17:29but were not when it first formed.
17:32From observing other solar systems forming all around us in space,
17:36we know that planets as close to their stars as we are to the sun,
17:40when they form, they're very hot and dry.
17:42There's probably some little bit of water around there,
17:44but really not very much.
17:47So what this means is any volatiles will basically be boiled away.
17:52If you have a molten surface, anything like water is going to get boiled away.
17:59Young Earth was a dry planet,
18:02devoid of all the precious volatiles needed for life.
18:07These materials must have been delivered to Earth after its formation.
18:16We think volatiles arrived in the early days of the solar system
18:21when the giant planets, including Jupiter, moved around
18:26and stirred up the contents of the solar system.
18:31As Jupiter moves, its gravity is pulling on all the objects in there,
18:35basically speeding them up.
18:37There's a little bit of chaos there in the first place,
18:39but now Jupiter is basically supercharging it.
18:42Jupiter's path sends countless asteroids and comets
18:46on a collision course with the Earth.
18:50It would have been utterly chaotic.
18:52This is a rain of large objects onto all of the inner planets,
18:56but these objects that came screaming into Earth were gigantic.
19:02Four billion years ago,
19:04a storm of giant asteroids and comets hits the Earth.
19:09Some are tens of miles wide.
19:12They bring the volatiles that helped fill the Earth's oceans
19:16and filled its atmosphere.
19:19But cosmic deliveries can both give and take.
19:25The importance of impacts for atmosphere could go either way.
19:28You could have a really big, really powerful impact
19:32that blows away the atmosphere of a small fledgling planet.
19:36Or you could have a bunch of small impacts of water-rich asteroids
19:40that are simply contributing water and volatiles
19:43and new chemicals to the surface
19:45that might help the atmosphere that's already there.
19:48When you think about an object coming to Earth,
19:50is it going to land on Earth?
19:52And if it does land,
19:54is it going to be an erosive event
19:57where material is lost from the Earth,
20:00or is it going to be an accretion event
20:02where the Earth gains material?
20:04Well, the devil's in the details.
20:07Details like the size of the impactor.
20:11One study suggests that asteroids between 60 feet and 3,300 feet wide
20:17add more to the atmosphere than they take away.
20:28And speed at the point of impact also matters.
20:34Asteroids are orbiting the sun.
20:36And when they fall towards the sun, they are gaining speed,
20:39they're gaining velocity.
20:41Imagine dropping a coin into one of those spiral wells.
20:45As the coin gets closer and closer to the middle,
20:47it spins up faster and faster.
20:52The closer an asteroid gets to the sun,
20:55the stronger the sun's gravitational pull
20:58and the faster the asteroid travels.
21:04So proximity to your star is a vital factor
21:07in how intense any impacts will be.
21:18It's possible that the Earth is the right distance from its host star
21:22so that when an impact happens, the energy isn't insanely high,
21:26it's just the right amount,
21:28that it's the right speed to make everything work.
21:32Supernovas seed the solar system with the elements to build the planets.
21:39Asteroids and comets deliver volatile chemicals to the surface of the Earth.
21:45Together, they create a habitable environment.
21:49So we need those impacts to happen to have life on Earth.
21:54Disasters created a planet primed for life.
21:59But it appears that even more mayhem and chaos
22:02are needed to trigger life itself.
22:17An asteroid tears through the solar system,
22:20hurtling through space at 40,000 miles an hour.
22:25Its destination? Earth.
22:29Will this space rock inflict unimaginable damage,
22:33or will it bring the spark of life?
22:40This idea of a spark of life,
22:42we've all kind of seen it in the Frankenstein movies, right?
22:45It's alive!
22:47This comes from legend, from myth, from history,
22:50that there's some sort of a spark
22:52that differentiates cold, inanimate matter from living stuff.
22:56And in some sense, it's kind of true.
23:02On Earth, we think this spark may have arrived over 4 billion years ago.
23:10The Hadean Eon was the time from the Earth's formation,
23:14about 4.6 billion years ago, to about 4 billion years ago.
23:18It's named after, literally, Hades.
23:21So the conditions on Earth were literally hellish.
23:27It was hot and soupy, a lot of water vapor around,
23:30high pressure, atmosphere, very intense heat.
23:33You wouldn't survive.
23:35The planet would literally kill you back then.
23:41It's shocking, and I mean really shocking,
23:44that the evidence of first life that we have on Earth
23:47dates to the Hadean Eon.
23:49This was a terrible place.
23:52Molten and poisonous and awful.
23:55And yet life somehow arose in all of that mess.
24:01June 2020.
24:03Japanese scientists simulate the conditions of this hellish planet
24:08and then try to recreate the spark of life.
24:13So what the scientists were trying to do was mimic those conditions
24:16and see what would happen if you smash a meteorite into the ocean back then.
24:20Could it produce sort of the same chemicals that we see life using today?
24:25They use a mix of carbon dioxide, nitrogen, water and iron
24:30to replicate the Hadean environment.
24:36Firing a mini-meteor at 2,000 miles an hour into this chemical soup
24:41triggers a reaction between the basic organic elements.
24:47Creating amino acids.
24:51We call amino acids the building blocks of life.
24:54Really, they're the building blocks of proteins,
24:57and life needs proteins to exist.
24:59But that's why they're so important.
25:01Without amino acids, there's no proteins.
25:03Without proteins, no life as we know it.
25:07The experiment proves that meteorite impacts can help build the components for life.
25:16But for these building blocks to come together and create life, we need more.
25:23It's like making a cake.
25:25You can put together the oil and the flour and the butter and the sugar,
25:28but if you don't put it in an oven, you're not going to end up with a cake.
25:31You're going to end up with something else.
25:34We thought that the violence of asteroid impacts prevented life from forming.
25:40Now, we think they could be an essential ingredient.
25:46If the asteroid impact is big enough and fast enough, it can punch right through the crust.
25:53Then you're getting geothermal heat, heat that bubbles up from the mantle.
25:57And it is certainly possible to get an asteroid impact that big.
26:02Large meteorite impacts can create hydrothermal vents,
26:06which some scientists believe were the cradles of life.
26:11They provide warm, wet environments and bring up chemicals from deep inside the Earth's crust.
26:19The perfect place for life to begin.
26:24As bad as those conditions seem to us,
26:27to the molecules that are beginning to combine and do their thing,
26:32that was a wonderful place to be.
26:34It could actually be that the conditions that are best for early life
26:37might actually be those just after an impact.
26:41So you have sort of this petri dish environment in which life could really thrive.
26:50These vents might be similar to those we see in the oceans today.
26:57These hydrothermal vents provide a little window
27:00into what the conditions on the primordial Earth would have been like.
27:04And the sort of chemistry that goes on in those hydrothermal fluids
27:09seems to be the right kind of chemistry for creating life.
27:16Once again, Earth got lucky.
27:22Impacts that could have destroyed everything
27:25Impacts that could have destroyed everything
27:29may have helped spark life into existence.
27:34I once heard this quote from Confucius,
27:37that creation is quiet, but destruction is loud.
27:43Well, these impacts were both destructive, but they also may have been creators.
27:50Earth leaves behind the Hadean Age.
27:54The planet calms and life takes hold.
27:58But disaster is our constant companion
28:01as we prepare to face a storm of deadly cosmic bullets.
28:07The Universe is a dangerous place for life.
28:10There are asteroid impacts,
28:17black holes,
28:21and exploding stars.
28:24But the most dangerous of them all
28:27is what we call the Big Bang.
28:30Black holes
28:33and exploding stars.
28:37But public enemy number one, cosmic rays.
28:43Lethal, energetic particles born in violent events.
28:48Cosmic rays are incredibly small,
28:51but travel so fast, near the speed of light,
28:54that they can tear through our DNA and damage it.
28:57You're full of DNA.
28:59If that DNA gets broken apart, guess what happens?
29:02That could lead to cancer and death.
29:05At first glance, these cosmic rays are the worst things for life.
29:09They're terrible.
29:11Despite their frightening rap sheet,
29:14cosmic rays may have played a crucial role in the evolution of life.
29:192020.
29:21Scientists at New York and Stanford Universities
29:24investigate biological molecules that have a twin.
29:29Mirror image versions called chiral molecules.
29:34The concept of chirality in chemistry
29:37is when you have two molecules, two chemicals,
29:40that are physically the same.
29:42They're made of exactly the same things,
29:45but their structure is different.
29:47And they're not just different, they're reflections of each other.
29:50It's literally called handedness,
29:52because look, here's my right hand with my thumb over here and my fingers over here.
29:56Here's my left hand with my thumb over here and my fingers over here.
29:59I can't wear a left glove on my right hand.
30:01There's nothing I can do to make these guys the same.
30:05And it turns out this is true not just for hands,
30:08but also for a large number of simple organic compounds.
30:13Things like amino acids or sugars,
30:16which are the building blocks of all life on Earth.
30:22Billions of years ago, early life may have had
30:25both left and right-handed DNA and RNA.
30:30But life chose to use mostly right-handed molecules.
30:34The reason may have been cosmic rays.
30:38When cosmic rays hit Earth's atmosphere,
30:42they degrade into even smaller subatomic particles called muons.
30:49Most muons spin in one direction.
30:53So we have these little muons, which are very energetic,
30:56and they're spinning a certain way.
30:58And when they hit a molecule, they interact with it.
31:01They can disrupt it, they can change it,
31:04Some scientists believe these spinning muons
31:07interact more readily with right-handed DNA and RNA.
31:14Triggering mutations.
31:17Some mutations are beneficial, but they have to get a chance.
31:20So if you have right-handed molecules and left-handed molecules,
31:24and they're both being hit by muons,
31:26the one that's hit more gets more chances to have a beneficial mutation.
31:31Cosmic rays may have given right-handed life an evolutionary advantage.
31:38Left-handed life could not compete.
31:42It's like throwing dice.
31:44If you're trying to get double sixes,
31:46and the left hand only gets to throw ten times,
31:48and the right hand gets to throw a hundred times,
31:50you're more likely to get double sixes with the right hand than the left hand.
31:56But the dice may not always be right-handed.
32:00But the dice don't always land in our favour.
32:04359 million years ago, Earth's luck ran out.
32:09And cosmic rays may have lived up to their reputation
32:13as the baddest particle on the block.
32:18Earth's oceans were teeming with marine life.
32:24And by this period as well,
32:26plants had started to colonise onto the continents and land masses,
32:31attracting animal life, insects, millipedes.
32:35And it's in this environment that Earth experienced
32:39one of the greatest mass extinctions in the history of life.
32:47Something killed off 97% of all vertebrate species.
32:53We call this wipe-out the end-Devonian extinction.
33:02One possible explanation? A supernova.
33:07When some dying stars explode, they fire out cosmic rays.
33:13This radiation bombards the upper atmosphere of the Earth
33:18and drives the chemistry of nitrogen turning into nitrogen dioxide,
33:23a gas which itself then reacts with the ozone layer and destroys it.
33:29Without the protective ozone layer, ultraviolet radiation from the sun bombards Earth.
33:37Radiation rains down for thousands of years,
33:41damaging the DNA of plants and animals.
33:49Many species die out.
33:54The end-Devonian mass extinction mostly affected marine life.
33:59This is where we see the greatest percentage of deaths.
34:04The oceans, once populated by fish the size of school buses,
34:09now host fish no bigger than a sardine.
34:14These smaller fish reproduce quickly.
34:18In the challenging environment, they adapt and diversify faster than larger species.
34:25Mass extinctions not only wipe the slate clean
34:28and provide other animals and other life forms an opportunity,
34:33it creates a sort of chaotic and complex environment
34:36that drives natural selection and evolution.
34:43If a supernova was to blame for this extinction event,
34:47scientists believe that the culprit was 65 light years away.
34:54Any closer and Earth's luck would have run out completely.
34:59It seems the existence of life is always balanced on a knife edge.
35:04One exploding star goes off a little bit too close to us
35:09and we are all destroyed.
35:14So there's this wonderful balance between just violent enough and too violent
35:19and we have been lucky enough to dance on that edge for four and a half billion years.
35:25This mass extinction reset life on Earth
35:28and paved the way for four-legged creatures, our distant ancestors.
35:37Cataclysmic events go hand in hand with human evolution.
35:42Some knocked us back and others, like the event 66 million years ago,
35:48gave us a push forward.
35:5966 million years ago, a massive asteroid crashes into the Earth.
36:06It triggers a huge extinction event.
36:10Without it, humans may have never evolved.
36:14At this time in Earth's history, we had these enormous plants and gigantic insects
36:19that actually would be incredibly terrifying if we saw them today.
36:25Pterosaurs sail through the air.
36:28Huge marine reptiles dominate the oceans.
36:31And the T-Rex is the king of the world.
36:35Then, a glowing object appears in the sky.
36:46I'm sitting on the beach, what was then going to be the Yucatan of Mexico,
36:51enjoying a drink with an umbrella.
36:54But up there in the sky, all of a sudden,
36:57approaching me at 40,000 miles an hour
37:00Approaching me at 40,000 miles an hour is Mount Everest,
37:05glowing thousands of times more intensely than the sun.
37:09And it's just seconds away from dropping on my head.
37:14A six-mile-wide asteroid slams into the Earth.
37:21The impact throws trillions of tons of rock and dust into the air.
37:29The rocks heat up as they fall back to Earth,
37:33setting the planet on fire.
37:40That beach holiday suddenly turns into absolute nightmare.
37:44The impact also throws up soot, choking the atmosphere.
37:50Now the skies are blotted out by all these materials,
37:53so the sun is no longer shining brightly on the surface.
37:58Plants need sunlight to photosynthesize.
38:02Without this vital energy source, many species die out.
38:08With their food source gone, plant-eating dinosaurs starve to death,
38:13followed by their predators.
38:16It was a huge disruption to all of life on Earth.
38:19The dinosaurs have been around for 160 million years at this point.
38:23That's no small amount of time, and in one event, they're gone.
38:28Again, the dice roll.
38:31Again, the dice roll is in our favor.
38:34Most dinosaurs become extinct, paving the way for the evolution of mammals,
38:40leading, eventually, to humans.
38:44Without the asteroid impact, we wouldn't be here.
38:49As a furry primate on this planet, I kind of like the KPG impact, right?
38:52I'm here because of it. We all are.
38:55Some plants benefited from the asteroid strike.
38:59To learn how plants changed after the impact,
39:02Smithsonian scientists examined thousands of tropical plant fossils
39:07from the time of the die-off.
39:12This disaster opened the way for new types of plants to develop.
39:16It transformed the plant kingdom,
39:19producing a richer and more diverse global ecosystem.
39:23Before the asteroid strike, conifers and ferns
39:26dominated the tropical forests of South America.
39:30But afterwards, falling ash from the impact enriched the soil,
39:35and fast-growing trees and plants began to thrive.
39:40But afterwards, falling ash from the impact enriched the soil,
39:45and fast-growing flowering plants took over.
39:51The impact was very hard to recover from,
39:54but it actually opened the opportunity for a greater diversity of plant life,
39:58which ultimately has benefited us as humans
40:00because it has allowed us to have more food sources.
40:04This new world order eventually gave rise to the modern Amazon rainforest,
40:10home to 10% of all species on Earth.
40:17It really destroyed and remade our entire environment.
40:21The world grew back. Of course it did. Here we are.
40:24But it changed everything.
40:27And another age may be just around the corner.
40:32We should absolutely expect that at some point in the future,
40:36and I'm not saying you should lose sleep over it,
40:39but at some point there will be another mass extinction.
40:47Maybe that will be the end of our days.
40:50The intriguing question is, what might come after humans on planet Earth?
40:57Catastrophe may be the universe's recipe for life throughout the cosmos,
41:03one that every planet must follow.
41:08Looking at our own history, life thrives on catastrophes.
41:12We need these disasters for evolution to work.
41:15So hopefully, and I hate saying this, I know how it sounds,
41:19hopefully these other planets have had terrible disasters as well.
41:24Think about the word disaster. It means bad star.
41:28It means that something has gone wrong, something that's dangerous.
41:31We are children of disasters.
41:36There's no way you get us without planets colliding,
41:40without asteroids and comets streaming through the atmosphere,
41:47without even stars exploding in supernovas.
41:54You are a child of that violence.
41:56That's part of the environment that we grew up in in a cosmic way,
41:59and I think that is tremendously beautiful.