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00:003.7 billion years ago, early life is on the brink of extinction.
00:10Colossal impacts, ferocious climate change, and total atmospheric collapse have turned
00:21paradise into hell.
00:24But this isn't Earth, it's Mars, and this is the violent history of perhaps the first
00:30life forms in our solar system.
00:33Could these Martians still exist today?
00:37Could they even be living among us?
00:57Scientists suspect that life may once have thrived on Mars, that the barren world we
01:04see today swarmed with Martians long ago.
01:08If I had to bet something incredibly valuable to me, if I had to bet my car on whether or
01:12not there is life on Mars, or evidence of past life on Mars, I'd take that bet.
01:19The building blocks for life are widespread in the universe, and early Mars could have
01:24been the perfect place to pull these ingredients together.
01:29If you had a recipe book with everything you need for life, you'd have things like water,
01:33organic chemistry, a stable surface, a thick atmosphere, well Mars had all of those.
01:39Mars satisfies every specific requirement for letting life get started.
01:46Life on Mars may have been inevitable, and we've sent a robot army to hunt for signs
01:51of it.
01:52But so far, it's been elusive.
01:55Our rovers, landers, and satellites haven't found life yet, but they have found evidence
02:01of something extraordinary.
02:06Mars was the victim of a devastating series of extinction-level events that rocked the
02:11red planet to its core, leading us to wonder if life could have started over multiple times,
02:20with generation after generation of Martians rising and falling through Mars' violent history.
02:30It seems likely that a first genesis of life could have occurred very early on in Mars'
02:36history, just as soon as the crust was cool enough to give it a solid foothold.
02:42The secret to this early life would have been a crucial ingredient, one shared by the young
02:48Earth.
02:50Dry, harsh Mars once had oceans.
02:54For life to get started, it needs some carbon, energy source, it needs nutrients like nitrogen.
03:00Those are likely to be present on Mars, they're present widespread on Earth.
03:04The essential requirement is really the liquid water.
03:10Picture Mars 4.5 billion years ago.
03:15Molten rock is cooled to form a solid crust.
03:19Water collects on the surface, forming primitive oceans.
03:25Rising clouds sweep across the steaming volcanic landscape, and in shallow pools of water,
03:31the Martians begin to emerge.
03:35But these first aliens are simpler than sci-fi would have us believe.
03:40We're probably not talking about little green men or women or whoever walking around on
03:44the surface of Mars.
03:45We're talking about something probably much, much smaller and simpler, single-celled life.
03:51It would look familiar, it would look just like bacteria on Earth.
03:54Little tiny, round and rod-shaped organisms.
03:58If this generation of bacterial Martian life really did exist, it was the first life to
04:04grace our solar system, multiplying inside the rock pools of Mars long before life took
04:11hold on Earth.
04:13Mars' small size would have given it a head start.
04:18Because Mars is smaller than the Earth, it would have cooled a little bit faster than
04:21we did.
04:22So early on in the life of the solar system, Mars may have been more like Earth than Earth
04:27was at the time.
04:31Let's go back a hundred million years after the sun formed.
04:35The surface of the Earth is still a molten lake, but Martian life could be thriving on
04:42the smaller, cooler world.
04:46But these first Martians won't have long to enjoy their time in the sun.
04:50Inescapable death is already on its way from space.
04:56A cosmic bomb so huge it would completely alter the shape of the planet, leaving it
05:03lopsided, the northern hemisphere crushed.
05:09Most planets are round, and that's just something you don't really give much thought to.
05:13But it turns out Mars isn't as round as it could be.
05:17The southern hemisphere, on average, has a higher elevation than the northern hemisphere.
05:23So in other words, if you were to start on the North Pole and walk all the way around
05:27to the South Pole, you'd be walking uphill essentially the whole time.
05:36So we call this difference between the northern and the southern hemisphere, we call this
05:40the crustal dichotomy on Mars, and it's been one of the biggest mysteries of the planet.
05:44You know, it's the first thing that you see about it, and you say, well, how could this
05:47possibly have happened?
05:49In 2008, scientists mapping the surface of Mars came up with an explanation for the massive
05:58dent in the planet, shown in blue.
06:01This basin, the biggest in the solar system, had to be the result of a massive impact.
06:08Called the Borealis impact, it blasted out a crater 6,500 miles wide and 5 miles deep,
06:15big enough to swallow the entire United States with room to spare.
06:20Something really big happened.
06:22In fact, the entire top half of the planet seemed to have practically been blown off.
06:27The only thing that can do that is a huge collision.
06:30And we're talking a collision with something the size of Pluto, perhaps.
06:36You're talking about an impact that makes the dinosaur killer impact 65 million years
06:41ago look pretty much like a wet firecracker.
06:464.5 billion years ago, the early solar system is filled with planetesimals and protoplanets.
06:54Asteroid-like leftovers from the planet-building process that created Mars and the Earth.
07:00One of these asteroids is huge, and it's on a direct collision course with Mars.
07:07Any microscopic Martians have just seconds to live.
07:12If this impact was happening today, and we were so unlucky as to be there to witness
07:18it, what you first would have seen is another moon in the sky.
07:24And then you would have looked back and seen, oh, it's getting bigger.
07:31As it came down, it would have filled the entire sky from horizon to horizon.
07:36And as it struck, the top would have still been well out into space.
07:43The impactor is 1,200 miles across, the size of Pluto.
07:48And as it hits, the energy of the impact shakes Mars to its core.
07:54The entire planet wobbles like jello.
07:58As it came down, it would have been hitting into the surface of Mars as fast as a bullet
08:04out of a gun.
08:06And it would have slammed into the surface and sent a shockwave out that would have been
08:10bigger than any earthquake ever recorded.
08:14It would have been like a tsunami of rock coming out and tossing us out of the way.
08:22The impact is catastrophic.
08:26It blows nearly half the planet's surface into space and turns what crust remains into
08:33a boiling lake of lava.
08:36You can't have an impact of that scale without almost melting the planet.
08:42It's not literally a planet-breaking event, but it's a planet-melting event.
08:45And it is the sterilization of the planet at that point.
08:53The surface of Mars was molten, its atmosphere blown into space, the oceans boiled away.
09:02If Mars was home to the first generation of life in our solar system, that life didn't
09:08stand a chance.
09:10It would take the surface of Mars 50 million years to recover from the impact.
09:19But what sort of planet will rise from the ashes?
09:23Compelling new evidence suggests that the conditions for life may have returned to Mars.
09:29But did life itself make a comeback?
09:34This impact was only a blip in time, and there was possibilities for life and the planet
09:40to recover.
09:594.5 billion years ago, an asteroid the size of Pluto slammed into the surface of infant
10:06Mars.
10:09It melted the surface of the planet.
10:11It blew the atmosphere into space, and it boiled away the oceans.
10:17If life had gotten a foothold on the planet, that life would have been completely exterminated.
10:24But some scientists believe this extinction could have been brief, and that life could
10:29have started again from scratch.
10:33One of the wonderful things to imagine is that there probably wasn't a single origin
10:36of life.
10:37It's not like it happened once, and then everything just went from there.
10:40Maybe there were multiple times that life got started and went extinct.
10:46Ten million years after the Borealis impact crushed the planet's northern hemisphere,
10:51Mars has cooled enough for its surface to become solid once more.
10:56The planet has some of the ingredients for life.
10:59The right molecules, a stable surface, and an energy source.
11:03But something's missing.
11:064.49 billion years ago, the surface of Mars is dry.
11:11And without water, life can't start over.
11:13And a second generation of Martian can never arise.
11:18As far as we know life, water is absolutely, fundamentally important to life.
11:242004, NASA's Opportunity rover lands on Mars.
11:31Part of its mission is to search for evidence that water returned to Mars after the Borealis
11:36impact.
11:38It's not long before Opportunity stumbles across something strange on the surface of
11:43a fossilized sand dune.
11:46Bizarre, round, metallic rocks.
11:52These rocks are called blueberries, and they're an important find for planetary geologists
11:57like Janie Radabaugh.
11:58Mars' fossilized sand dunes also exist on Earth, and Utah's petrified dunes are also
12:06littered with blueberries.
12:08This is really exciting because we've seen the exact same thing on Mars.
12:14Finding blueberries on Mars is significant because the Borealis impact melted the planet,
12:19so anything found on Mars today must have formed after the impact.
12:25But crucially, these nodules of iron oxide form deep underground and in the presence
12:31of water.
12:33In order to form one of these little blueberries, there needs to be huge amounts of water flushing
12:38down through the fossil sand dunes.
12:41And as it does that, it carries with it all of the iron oxides around each sand grain.
12:46And just one tiny little one like this, now this is maybe about an ounce of iron, maybe
12:50a little bit more.
12:52And in order to get an ounce of iron to concentrate into this blueberry, you need to have a thousand
12:56gallons of water.
13:00Blueberries form deep inside sandstone.
13:03But over thousands of years, wind erosion blows away the softer rock, leaving just the
13:09blueberries behind.
13:11If we walk to the edge of this pile of blueberries, we can see the process by which they're actually
13:19eroding out of the rock.
13:20The blueberries right here are contained within this fossil sandstone layer.
13:26The winds are blowing in this direction, down the layers, and they're actually eroding out
13:31the soft sandstones right here and leaving behind the very dense iron nodules.
13:37And as they pluck themselves out of the rock, they roll down the hill and then collect right
13:41here in between layers.
13:45We know we've found conditions just like this on Mars.
13:47We have fossil sand dune layers.
13:50We also have blueberries all over the surface.
13:53So we know the same kinds of things had to have happened on Mars that have happened here.
13:57There has to be water flowing through the rock, gathering iron, and then there has to
14:00be a huge amount of wind to strip away the fossil sand dunes.
14:07For blueberries to exist on the surface of Mars today, the red planet must have gotten
14:12its water and its atmosphere back after the catastrophic impact.
14:17With liquid water on the surface, the ingredients of life might have combined once again to
14:23create a second generation of Martians.
14:27But where did this water come from?
14:30The answer is surprising.
14:33It could have been in the planet itself.
14:35Water is incredibly abundant.
14:37We know that there's water deep, deep, deep in the Earth's mantle.
14:42And so it's entirely possible that on Mars there was water so deep in the planet that
14:46even after this catastrophe, it came back up.
14:50On the Earth, scientists have used the seismic waves of earthquakes to detect an ocean's
14:56worth of water chemically embedded in minerals deep underground.
15:01A similar water source could have been hidden hundreds of miles below post-impact Mars,
15:07and volcanoes could have brought that water back to the surface.
15:12One way for water to get from deep underneath the surface to the surface of the planet would
15:16be through geologic activities, volcanoes, for example.
15:20We know that volcanoes spew out a lot of gases on Earth, including water vapor, and we see
15:25volcanoes on Mars.
15:30Mars is home to the largest volcanoes in the solar system.
15:33The biggest of all, Olympus Mons, is over three times taller than Mount Everest.
15:424.49 billion years ago, volcanoes spew lava, spiked with water, into the atmosphere and
15:49create ferocious rainstorms that flood the surface of Mars.
16:01Over tens of thousands of years, Mars becomes a watery world once again, with the perfect
16:07conditions for a second generation of Martians to rise up.
16:13It would seem that when you have a massive collision like what happened to Mars, it would
16:17be game over for life.
16:19But there's something more complicated going on.
16:22Maybe that asteroid impact kicked off an entirely new cycle of life on Mars.
16:28In theory, four billion years ago, a second generation of single-celled bacterial life
16:34arose on Mars, and for the very first time, there was life on two planets in the solar
16:40system.
16:42One hundred forty million miles away, life on Earth had just begun.
16:47And thanks to Earth's stable climate, it would one day evolve into us.
16:56But the outlook for Mars was very different.
16:59Evidence from the Mars Reconnaissance Orbiter suggests an icy apocalypse was about to strike.
17:07For Mars' second generation, winter was coming.
17:29Four billion years ago, the first life has arisen on Earth.
17:38But on Mars, life may be starting out for a second time.
17:43It's possible that Mars had life before Earth did.
17:47It got wiped out and then got started again by rehydrating the planet.
17:54A planetary collision has blown away Mars' atmosphere and oceans, along with any life.
18:00But giant volcanoes have brought water back to the surface from deep within the planet.
18:06This could have allowed for a second generation of life to rise up.
18:10These Martians are about to be tested to their limits by catastrophic climate change.
18:182008, NASA's Mars Reconnaissance Orbiter flies high over the surface of Mars.
18:34Its ground-penetrating instruments peer deep below the surface, aiming to unlock Mars'
18:39geological secrets.
18:41As it scans near Mars' equator, the orbiter spots something that has no right to be there
18:47– a vast underground glacier.
18:52One mile thick and three times the size of Los Angeles, ice on this scale should only
18:57form at the frigid poles.
19:00The only explanation?
19:03Mars must have been tipped over, with its equator tilted away from the sun.
19:09The tilt on Mars' axis has actually changed significantly over time.
19:13And in non-systematic ways, it just happens randomly that it will start moving.
19:18And so there are some models that suggest that Mars has actually been almost tipped
19:22over on its end.
19:26Most planets wobble.
19:27And from time to time, they wobble so much, they can tip over, leading to super winters.
19:35If that happened here on Earth, Los Angeles could become the Arctic.
19:39Well, you can imagine something similar would happen on Mars, how drastic the change would
19:43be.
19:44You're used to seeing the sun overhead.
19:47It's very warm.
19:48There's probably liquid water.
19:49And as the planet starts going this way, the sun is not going to rise as high in the sky.
19:56So basically, you might not see sunrise for half a year.
19:59And any water that's there is going to be frozen solid.
20:043.9 billion years ago, Mars is tilting by as much as 80 degrees.
20:10Winter temperatures drop below minus 125 degrees Fahrenheit.
20:17As the polar ice sheet spreads quickly toward the equator, liquid water is frozen solid
20:22along with any potential Martians.
20:26The water that drives the biochemistry of life freezes inside the tiny bacteria.
20:33Ice crystals form and puncture the Martians' cell walls until eventually they die.
20:42Every 120,000 years, the tilt of Mars changes.
20:46As again and again, the planet's chaotic wobble flips the Martians in and out of the deep
20:52freeze.
20:54Any second generation of life on Mars is left in tatters.
21:02Meanwhile, on Earth, our ancient ancestors have it easy.
21:14The Earth's wobble and its seasons stay relatively stable, and it's all thanks to our secret
21:20weapon, our oversized moon.
21:25The interaction of our planet and the moon means that the axis of our rotation is very,
21:30very stable.
21:31The seasons return year after year, century after century, for billions of years.
21:39Our moon's enormous mass exerts a huge gravitational pull on the Earth, stabilizing the wobble
21:45of our planet and keeping our climate in check.
21:50Without the moon, the early Earth would have wobbled just as wildly as Mars, and our ancestors
21:56could have faced the same icy fate as the early Martians.
22:02Mars doesn't have a big moon.
22:03It has two little tiny moons that don't really affect it much.
22:08So if the Martians were killed the first time by a giant impact, they may have been killed
22:12a second time by Mars itself not being stable and flipping over and having catastrophic
22:19super winters and super summers, basically, mega-catastrophic climate change.
22:27On Mars, the outlook for life seems bleak, but the brutal conditions that drive Martian
22:33life to the edge of extinction may also have pushed it to adapt and evolve.
22:40We know this because on Earth, organisms known as extremophiles have evolved to live in the
22:46most severe of circumstances, from boiling hydrothermal vents to the deep freeze of glacial
22:53ice.
22:54When the going gets tough, life seems to get tougher.
23:00Maybe the Martian super winters gave rise to a third generation of life, a super tough
23:06army of bugs able to survive the harshest of climate swings.
23:13What we see on Earth is that life evolves to occupy whatever niche it lives in.
23:19And that evolution takes time.
23:21So as the environment changes, life changes with it.
23:25If there are sudden changes, then life forms can't cope with it and many die away.
23:31Those that survive, they continue on.
23:343.8 billion years ago, a third generation of life could have thrived on the surface
23:40of Mars.
23:43Evolved from a handful of its predecessors to make it through Mars' super winters, it's
23:48the toughest Martian life yet.
23:51But as the super winters end, the challenges for life on Mars are set to get worse.
23:58Another extinction-level event is on the way.
24:01Mars' atmosphere is being ripped away molecule by molecule.
24:06Could this be the killer bunch that wipes out the Martians for good?
24:26Imagine Mars 3.8 billion years ago.
24:31It's a warm, wet world, and super tough bacterial life is thriving.
24:38But these Martians are not the planet's first inhabitants.
24:46The first generation of Martian is vaporized by the huge Borealis impact.
24:53Perhaps life starts over from scratch, but endures a series of extreme climate swings.
24:59Only the toughest Martians make it through.
25:08But another disaster is about to strike, and this catastrophe will test even the strongest
25:14Martians.
25:17They're about to lose the most basic ingredient of life, liquid water.
25:23You really have to appreciate how difficult it is to have liquid water on the surface
25:27of a planet.
25:29We know that life works so well when there's liquid water around, but you need just the
25:34right balance of air pressure and temperature.
25:38Without air pressure weighing down on it, liquid water will evaporate from the surface
25:43of a planet, whatever the temperature.
25:47That air pressure is generated by the presence of an atmosphere.
25:52In a lot of ways, that atmosphere serves as a kind of a lid stopping down the water from
25:55escaping to space.
25:56It's very important to have that atmosphere.
26:013.7 billion years ago, life on Earth enjoys warm oceans and a thick atmosphere.
26:08But on Mars, a third extinction-level event is gaining momentum.
26:17The atmosphere is slowly being stripped away, and Mars' great oceans are starting to evaporate.
26:27The fate of life on both planets now rests on the strength of their magnetic cores.
26:34It turns out that the existence of an atmosphere on Earth may rely on the magnetic field, because
26:39what our magnetic field does is it protects us from the onslaught of this wind of subatomic
26:46particles that the sun is blowing out all the time.
26:49We call this the solar wind.
26:54And if we didn't have a magnetic field to basically catch and deflect those particles
26:58gently, they would directly slam into the Earth's atmosphere.
27:02If you think of the magnetic field as a windbreaker from the solar wind, once we lose that protection,
27:09that planet becomes very vulnerable.
27:14The Earth's magnetic core has stayed strong for 3.45 billion years, as super-hot molten
27:20iron churns over and over within the planet like a lava lamp.
27:27Churning iron creates electricity, which in turn generates a magnetic field that rises
27:32up around the Earth, acting like a magnetic shield, protecting our atmosphere from the
27:37ravages of the solar wind.
27:403.8 billion years ago, Mars had a molten core and a magnetic field, but something caused
27:47its shield to drop.
27:49Did Mars' small molten core simply get too cold to function?
27:54Or did something else kick-start this third great extinction of Martian life?
27:59A new and controversial theory points the finger partly at the ancient Borealis impact.
28:08A giant impact of this scale can affect the range of temperatures from the hot inner core
28:14to the cooler outer mantle.
28:174.5 billion years ago, the impact that vaporizes the first generation of Martian life also
28:24drives heat into the planet, increasing the temperatures in the outer mantle.
28:29The heat inside the planet evens out, and the metals slowly stop churning.
28:35If there's less of a temperature gradient, that makes it harder for this dynamo process
28:40to drive a strong magnetic field.
28:44For hundreds of millions of years, Mars' magnetic field shuts down.
28:51When Mars lost its magnetic field, all of a sudden, it was completely vulnerable to
28:55the solar wind.
28:57The solar wind could break apart and carry away the Martian atmosphere.
29:023.7 billion years ago, super-tough Martian life faces annihilation.
29:15Bit by bit, the atmosphere is being swept into space.
29:20The air pressure is dropping across the planet, and most of Mars' water has already boiled
29:25away.
29:30The chances of survival without this precious liquid are remote.
29:35But for the Martians, there's an even more immediate danger.
29:39With no magnetic field and no thick atmosphere, the surface of Mars feels the full force of
29:46the sun's radiation.
29:55If you're a microbe on the surface, you would have to make do with very little atmosphere,
30:00no water, this flood of ultraviolet light from the sun, and these particles which are
30:04slamming into you all the time.
30:08The Martians are bombarded by radiation from the solar wind.
30:13It rips their DNA apart.
30:17Without an atmosphere, the surface of the planet is sterilized.
30:22But is this really the end for Martian life?
30:26Life is so tenacious, it can survive even those incredible catastrophic changes, and
30:31it may still be there today.
30:34To survive the radiation, Martian life would have had to have moved deep underground.
30:43In this protected subterranean environment, it may also have found a source of liquid
30:48water.
30:49And if that happened, could the Martians still be there today, waiting for us to drop in
30:56and say hello?
31:13Since the 1960s, robotic probes and landers have been searching the surface of Mars for
31:19signs of life.
31:22But have they been looking in the right places?
31:25The surface of Mars is a waterless desert that's bombarded by harmful radiation.
31:32If a fourth incarnation of Martian life is alive today, many scientists think it'll have
31:38to be deep underground.
31:41Like the surface of Mars, you may have all the conditions you need for life.
31:44There may be some liquid water down there, and you're also protected from the intense
31:48radiation that you find on the surface.
31:55Scientists are split on the best underground places to search for Martian life.
32:02But if Janie Radabaugh were on Mars, she would head to the nearest sand dune and start digging.
32:10Here you can see this is wet sand just below the surface.
32:14This is the perfect environment to be able to house life.
32:18Even in the very driest deserts on Earth, in between the sand dunes, in the interdunes,
32:23you can find water percolating up from springs that come up from deep under the ground, perfect
32:28for life to form and grow.
32:30And if you just keep on digging down into the bottom of the interdune, maybe you would
32:35reach the water table.
32:36And if you reach the water table on Mars, now you have all the conditions just right
32:41for life.
32:42This is my bed.
32:43This is where I'd go, right between the dunes.
32:47Digging for Martian life in the desert is one option.
32:51But some scientists have very different ideas.
32:54And planetary scientist Nina Lanza would need to pack a rope and a flashlight for her search.
33:01So if I were to go to Mars to find life, I would go to a lava tube.
33:06Lava tubes are made by ancient volcanoes, the empty leftovers from underground lava
33:11flows.
33:13Today, they form deep tunnels shielded from radiation and shut off from the harsh Martian
33:19climate.
33:20We've never been in a lava tube on Mars, but it is absolutely possible that there's liquid
33:25water.
33:28So that's an environment where you could have some moisture, you could have a little warmth,
33:32you're protected from radiation.
33:34I think that a Martian microbe would be very happy there.
33:42Finding life on Mars would be a monumental human accomplishment.
33:47But there is a danger.
33:48By exposing Martian life to life from Earth, could we unwittingly set off yet another extinction
33:55event?
33:57Humans have been one of the most effective extinction mechanisms of life on Earth.
34:02The interesting question will be, will we produce a similar calamity on Mars?
34:08If humans someday go to Mars, then we will be an invasive species.
34:12And if there is some Martian life that's hanging on in some niche, we could be their ultimate
34:16destroyers.
34:18So we have an ethical responsibility to preserve whatever life may be on Mars.
34:25The problem isn't us, it's the bugs in and on our bodies.
34:30The average human has 10 to 20 trillion bacterial hitchhikers.
34:35If we go to Mars, we'll be taking our tiny companions along for the ride, and any one
34:41of those bugs could turn out to be a deadly competitor for Martian life.
34:49It's NASA engineer Mujige Cooper's job to keep Mars rovers bug-free.
34:55But keeping astronauts clean, that's a whole different matter.
35:00We bake out our spacecraft hardware at 110 degrees Celsius for at least 50 hours to prevent
35:06the contamination of Mars.
35:08Unlike spacecraft, we cannot bake humans out.
35:12We will not survive those temperatures.
35:19Unless we find a way to keep astronauts bug-free, exploring Mars with robots is our best option
35:25for keeping the Martians safe from harm.
35:30But what will happen when our robots finally find that life, and we look deep into the
35:35workings of our extraterrestrial neighbors?
35:40What will the Martians turn out to be like?
35:45Our example, where DNA is the organic molecule that carries the information of life, we don't
35:49even know if that's going to be the rulebook in other places.
35:54Finding any evidence whatsoever on Mars would help us better understand what else is possible.
36:02Will the Martians be different than us, made from different materials and with a different
36:08biochemistry?
36:10Or will they seem shockingly familiar?
36:14Some scientists think that the very first Martian life may not have stayed on Mars.
36:20It may have come here.
36:23It's not that far-fetched to think that life could have jumped from Mars or back and forth
36:28from Mars to Earth.
36:30If the Martians came to Earth, could they have seeded life on our planet?
36:35Maybe the Martians aren't dead.
36:37Maybe I'm a Martian.
36:38Maybe you're a Martian.
36:53We've sent a robot army to Mars, and what it's found is astonishing.
37:03The possibility that life could have arisen there, perhaps more than once, with different
37:10generations of Martians emerging from the ashes of catastrophic extinction events.
37:19Life could still be sheltering below the surface of Mars right now.
37:28But there's another possibility that's truly astounding, that Martians aren't just hiding
37:34out on Mars.
37:36They're thriving right here on Earth.
37:42I might be a Martian.
37:43You might be a Martian.
37:46We might be from another planet.
37:48We might have already traveled and lived on two planets as life forms.
37:53Not as a species, certainly.
37:55But our ancestors may have come from another planet, and that is mind-blowing.
38:02The idea that our ancestors could be Martians is a new take on an old theory called panspermia.
38:10According to the theory, life on Earth began when a space rock filled with alien bacteria
38:16landed on the Earth, and every living thing we see today, including us, evolved from those
38:21cosmic hitchhikers.
38:25The idea of panspermia has been around for centuries, but had a resurgence when scientists
38:30determined that life on Earth may go back four billion years to the end of a sustained
38:35attack of asteroid showers known as the Late Heavy Bombardment.
38:42There were a lot of objects from the outer solar system, comets and asteroids, all kinds
38:45of things, coming into the inner solar system and slamming into the planets.
38:51Conventional wisdom suggests the objects hitting the Earth at the time were leftover debris
38:56from the formation of the solar system.
38:59But a very controversial idea suggests these space rocks were actually all pieces of Mars
39:08thrown off in the Borealis Basin Impact when a huge object blasted into Mars.
39:15The timing links up really well for the Borealis Basin Impact.
39:22If you calculate how much debris that would have thrown out into space and when it would
39:27have had to have happened, according to the Martian geologic record, it coincides with
39:33the Late Heavy Bombardment, it's possible that the debris from the Borealis Basin Forming
39:43Impact might have come to Earth and rained down on us and made the Late Heavy Bombardment,
39:48seeding the Earth with bacterial spores from Mars.
39:51Now this is just a hypothesis.
39:53We don't know this for certain.
39:54We don't have evidence.
39:56But it is physically possible for that to have happened.
40:01Was the Earth seeded by microscopic Martians blown into space by the Borealis Impact?
40:09It sounds crazy, but the science stacks up.
40:13We know that simple life is tough, able to survive in the cold vacuum of space.
40:19And the timing of the Borealis Impact works out well for the rise of the first organisms
40:24on Earth.
40:28Crucially, we know that rocks ejected from Mars can make it all the way to Earth because
40:34they're still crash landing here, even today.
40:38One of the coolest things I've done as a scientist is held a piece of Mars in my hands.
40:43Now we never had a mission that returned a sample from Mars.
40:46We had to come about it a different way.
40:47And it turns out we have meteorites that we are 100% sure are bits of Mars.
40:53They were actually exploded out during huge collisions, and eventually they fell on the Earth.
41:03Four different generations of Martians, each of them facing a different planetary catastrophe.
41:11But despite enormous odds, Martians could still be alive today, buried deep under the
41:17surface of Mars, or maybe even thriving on Earth.
41:22If life is really that tenacious, that it can come back and keep coming back and keep
41:27coming back, that gives me a lot of hope for life in the universe.
41:31That tells me that life is maybe tough.
41:34Maybe individuals are fragile, but maybe life itself is tough.
41:39For now, all we can do is speculate, until future generations develop the technology
41:45to visit the red planet and grab our first sample of extraterrestrial life.
41:53That's going to change everything.
41:54We're going to have another example of how life started and how life works.
41:58And even if it's something that's dead, we knew it was there.
42:01The universe will never be the same again.