How the Universe Works - S04E05 - Dawn of Life
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00:00There is an unbreakable bond between life on Earth and the stars above.
00:13Everything we see up there and down here is made from the same star, atoms.
00:21The question is, how did these atoms come together to make us?
00:28And are we the only life asking this question?
00:48Everything we see in the universe is made from the same building blocks.
00:55The universe is only made up of a handful of basic ingredients, hydrogen, helium, lithium,
01:01carbon, and so on.
01:02All of these chemicals in different proportions are what make us up, and these same chemicals
01:08in different proportions make up everything.
01:13The same chemicals that form galaxies and stars do something amazing on Earth, perhaps
01:19even unique.
01:21They become living things, organisms that can grow, reproduce, and think.
01:30We are bits of the universe made conscious.
01:32I think that's a, it's a biological miracle.
01:35You look out into the sky and you know you're connected to that somehow.
01:39It's pretty fantastic.
01:44The story of life on Earth actually began long before the Earth even existed.
01:59Immediately after the Big Bang, the universe was a vast cloud of hydrogen gas.
02:06Pockets of the gas cloud collapsed to form stars.
02:12The stars turned hydrogen into more complex atoms and molecules.
02:21I don't think there's any way you could make life out of just hydrogen.
02:24You need other compounds to give you the more complex chemistry.
02:28The start of life was really the start of the first stars, probably about half a billion
02:32years after the Big Bang.
02:37Deep inside the cores of these early stars, heat and pressure crushed hydrogen atoms together
02:44so powerfully they fused, creating helium atoms and releasing a burst of energy.
02:54Over time, helium atoms fused together too, creating carbon, nitrogen, oxygen, and even
03:01heavier atoms.
03:04For hundreds of millions of years, ancient stars built up all the elements that make
03:08up our solar system today, including the atoms in your body.
03:15But in doing so, these stars paid a catastrophic price.
03:20Drained of energy, the ancient stars collapsed and then exploded, a supernova, spreading
03:28their chemically rich stardust across space.
03:31The iron in your blood, the calcium in your teeth and your bones, these were created in
03:36a supernova explosion, probably different stars that blew up billions of years ago,
03:43seeding the space around them with this stuff.
03:49We are the product of not just one stellar explosion, but many stellar explosions, and
03:54the atoms in our left hand probably came from a different star than our right hand.
03:59The carbon, nitrogen, oxygen, iron, all of that was only created in stars.
04:03And the only way it could get here on Earth is if those stars exploded and that material
04:07was later amalgamated in our solar system.
04:13Blasted into space, these complex atoms pepper the clouds of gas that then themselves become
04:19the nurseries for new stars.
04:234.6 billion years ago, one particular cloud began to collapse under its own gravity, and
04:31the sun ignited.
04:34Most of the ancient stardust was sucked into the sun.
04:37What little remained went on to form the asteroids, comets, planets, and even the plants and animals
04:43that inhabit the Earth today.
04:48I actually think of myself as a very complicated rock.
04:51I am made of things like iron and copper and manganese.
04:54When you sit down on a mountainside and you're there with a rock, those are your cousins
04:58too.
05:01Thanks to the remnants of ancient stars, the Earth formed with all the atoms needed to
05:05create both rocks and life.
05:09But what is it that distinguishes life from mere chemistry?
05:15You're essentially three main parts to a living organism.
05:21You've got to have some metabolism or some kind of system of chemical reactions that
05:26powers your life.
05:28You've got to have some kind of bag or a sack that walls you off, your internal systems
05:34from the outside environment.
05:38And thirdly, you've got to store some kind of blueprint, some kind of description of
05:42yourself.
05:44Three things set life apart, a power source, a protective sack, and the blueprints for
05:51making duplicates of itself.
05:54On Earth, every living thing has the same kind of blueprint.
05:58It's a chemical code called DNA.
06:02DNA contains the instructions for how to build the cell's engine using small molecules called
06:08amino acids.
06:11DNA also tells the cell how to make lipids, the fatty molecules that form the protective
06:16sack.
06:17And that's it, the most basic form of life, a cell.
06:24The chemistry set for life is actually quite simple.
06:27It's 20 amino acids, it's a few nucleotide bases for making DNA and RNA, a few lipids,
06:33and that's it.
06:36Think of it as like a Lego kit.
06:41Scientists wanted to find out where the ingredients for this simple kit of life came from.
06:48In the 1950s, chemist Stanley Miller set up an experiment to find out.
06:55He filled a series of flasks with water vapour and volcanic gases to recreate the early atmosphere
07:01of the Earth.
07:05And then he sent an electric spark across the mixture to simulate lightning.
07:12The result was a foul-smelling gunk that included one of the three basic building blocks for
07:19life.
07:24We find produced in this experiment some amino acids, some of the same amino acids that are
07:30produced in life.
07:32Before Miller's experiment, it was assumed that this kind of organic material could only
07:36be produced by biology, which is why it was called organic.
07:40Miller showed that it's not biological.
07:42It's occurring, we would expect, in lots of different places.
07:50Because amino acids were so easy to make, scientists wondered whether these same molecules
07:55could have formed in the gas cloud that made the sun, even before the Earth itself was
07:59born.
08:00If the theory was right, then asteroids, the leftovers from this period of planet building,
08:10might still contain these ancient molecules today.
08:19Proof arrived in the 1960s, when a space rock older than the Earth fell on Murchison, Australia.
08:26When you pick up pieces of this meteorite, it just reeks, it stinks of kind of organic,
08:32volatile chemicals.
08:35And when you analyse what's in there, we find there's plenty of amino acids that are the
08:39building blocks of proteins.
08:42We find kind of fatty molecules that make these envelopes, these membranes around all
08:47of our cells, and incredibly, we find the bases of DNA.
08:55The Murchison meteorite proved that the component parts of a living cell are everywhere.
09:02They were in the clouds of stardust that formed the Earth.
09:06The atmosphere of the early Earth made more, and asteroids containing organic building
09:11blocks continued to rain down for millions of years after the crust cooled.
09:17The early Earth was steeped in the building blocks for life.
09:22And how these building blocks come together, in just the right way to form a cell, could
09:29be described as miraculous.
09:49The Earth, four billion years ago.
09:53There was land, sea, and a newly formed moon.
10:00The moon was much nearer than it is today.
10:03Its close proximity raised huge tides that swept miles inland.
10:09Volcanoes belched choking fumes into the broiling hot atmosphere, and asteroids and comets rained
10:16down from space.
10:19It was a time of no oxygen in the atmosphere.
10:23It was much hotter because of the radioactive heating left over from the accretion of the
10:29Earth, the impact heating left over from the accretion of the Earth.
10:33Incredibly alien place, and not anything like the Earth we see today.
10:38And yet life arose there.
10:40If we're going to search for the origins of life on Earth, we have to bear those conditions
10:44in mind.
10:48Similar conditions exist on Earth today.
10:52Scientists study them to understand how life could have come to exist on our hostile young
10:55planet.
11:00The early Earth wouldn't have had great continental land masses like we see on the globe today,
11:06but more like archipelagos of volcanic islands.
11:09We would have had these enormous tides washing miles upland and then receding back again,
11:15and leaving behind them something a lot like this landscape we see here with rock pools
11:20of warm, steamy water.
11:26Some scientists believe life could have started in these warm rock pools.
11:32The building blocks of life were suspended in the water.
11:36They would have concentrated together as the water evaporated in the strong sunlight, forcing
11:41the molecules to interact.
11:45At this geothermal site in Iceland, a similar process concentrates minerals into a thick,
11:50white paste.
11:51One of the most important kinds of chemicals that might have been concentrated down in
11:58these volcanic rock pools on the early Earth for the origins of life are lipid molecules,
12:03so fatty molecules.
12:05And these are able to pull off a very clever trick.
12:09They naturally self-assemble.
12:15On the early Earth, individual lipid molecules floated free in the oceans, but trapped together
12:22in rock pools, these fatty molecules joined up to form bubbles.
12:29And this is important for the origin of life because they form the outside membrane of
12:34all cells of all life on Earth.
12:36And to show you what I mean, I can use these fishing floats here.
12:40Now, these fishing floats have an end which hates water and an end that loves water, just
12:46like a lipid molecule.
12:47Let's see what happens.
12:48So no matter which way they go in, they've all naturally orientated themselves with one
12:53end sticking out and one end staying in the water, and we can see they've clumped together.
13:01The fatty molecules were drawn to each other like oil droplets on the surface of water.
13:06To form a thin membrane.
13:10And whenever these waters lapped against land, the films would have coated the inside
13:15of the volcanic rocks with oily bubbles.
13:21This rock has got a very spongy texture to it, so if these lipid molecules form naturally
13:26into these films and bubbles and line the inside of these vesicles in the rock, you've
13:32essentially built a protocell.
13:36With the protocell in place, the fatty sack would have been filled with organic molecules
13:41like amino acids from the concentrated soup left behind in the rock pool.
13:49Perhaps these simple building blocks joined together to form proteins and DNA.
13:56Maybe that was a great environment to get things concentrated.
13:59You had water, but you had a chance for things to sink together into shallow pools where
14:04molecules could really be forced to interact.
14:09Rock pools show us that it's possible for the organic machinery of cells to assemble.
14:14But as a place for the origin of life, rock pools had a huge drawback.
14:27Four billion years ago, the sun's UV radiation was up to a thousand times stronger than it
14:32is today.
14:37This intense radiation would have destroyed the DNA that formed in the shallow rock pools.
14:45So in an effort to understand how a cell could have come together away from the sun, scientists
14:52took a closer look at what a cell needs to work.
14:56You can think of it like an industrial city.
15:02Tiny structures inside the cell operate like factories.
15:06They take in raw materials and transform them into more complex forms, such as the hardware
15:11to build new cells.
15:14And just like a city, cells also need energy to keep their industrial units running.
15:20Some scientists believe that the key to the origin of life is hidden in the way life gathers
15:25and uses energy.
15:28It all comes down to energy.
15:30Energy is what drives complexity and development in technology.
15:33We see it in human history.
15:35It drove development and complexity of the story of life.
15:42Today, cells have complex biological power stations built inside them.
15:48These structures help to drive chemical energy in and out of the cell membrane.
15:54And this chemical flow ultimately provides the cell with power.
16:00But the very first cell wouldn't have had the luxury of such a complex system to generate
16:06power.
16:09And the energy from the sun would have been tainted with lethal radiation.
16:15So the quest to find the place where life first arose led scientists to search the Earth
16:21for a shady spot with chemical energy already moving through it.
16:27In the 1970s, scientists embarked on a daring submarine mission to a long volcanic crack
16:37on the bottom of the Pacific Ocean.
16:42They discovered tall chimney-like structures belching hot volcanic water.
16:50Incredibly, these structures were covered with life.
16:57What really blew people's minds when we first discovered these was the ecosystems,
17:02like oases of life, huddled around these black smokers miles deep in the water and the sea
17:08where the light of the sun never shines.
17:15Before these vents were discovered, nobody knew that life could exist without light.
17:20But here were creatures thriving on the chemical energy jetting directly from the seabed.
17:29Scientists began to wonder if the same chemical energy could have kick-started life.
17:33But there was a problem.
17:38These vents that were first discovered were really too hot to be a site for the origin of life.
17:54In the year 2000, scientists working 14 kilometers to the west of the Mid-Atlantic Ridge
18:00discovered a new, much cooler type of vent.
18:04They named them alkaline vents, after their unique chemistry.
18:10What we find with these alkaline vents, we have this warm, mineral-rich water seeping out of the seabed
18:17and then kind of mixing and interacting with the cold seawater around it,
18:21is it deposits the solids and kind of builds up these vast chimney, kind of towering type structures.
18:30The temperature inside the towers was perfect for organic molecules to assemble into more complicated forms.
18:39Scientists then searched the vents for a source of energy that could potentially turn chemistry into biology.
18:50Laurie Barge is part of a NASA team that grows alkaline vents.
18:58Now we're beginning to test in the lab what specifically could be happening on vents on the early Earth.
19:03We have to take into account the conditions of the early atmosphere, the early ocean,
19:07the type of ocean crust and reactions that would have been occurring.
19:12Laurie starts by injecting alkaline fluids into a simulation of an early Earth ocean.
19:17The ocean here contains dissolved iron, as it would have on the early Earth.
19:21And then the chimney that you're seeing is the precipitate that forms
19:26when you have two contrasting solutions like this.
19:30A delicate chimney builds up inside the flask.
19:35And because this structure is alkaline, it reacts with the acidic water around it,
19:41drawing chemical energy into the walls of the chimney.
19:46And this chemical flow is almost identical to the one generated by living cells today.
19:55But energy and temperature aren't the only features these alkaline vents share with living cells.
20:03The curious thing about these alkaline vents is that the pockets and the pores
20:08and the kind of channels and tunnels we find riddling their way throughout these structures,
20:12these chimneys, are about the same size as cells.
20:21In the early Earth, these tiny pockets would have provided a warm crucible
20:25for the three basic building blocks of life to come together.
20:32Chemical energy flooding through the chimney walls
20:35may then have jump-started the tiny metabolic engines inside these protocells.
20:42After millions of years, the protocells could have developed a way to make energy for themselves.
20:49Broken free.
20:52This could have been the moment chemistry became life.
21:04Alkaline vents are the leading theory for the origins of life on Earth.
21:11But the theory faces competition.
21:17Some scientists believe that life arrived on Earth from another planet
21:23and that our ancestors were aliens.
21:30The Earth, four billion years ago.
21:35The crust has cooled.
21:38It's warm and wet.
21:41The asteroids and comets that brought water and organic molecules to the Earth
21:46are a distant memory.
21:49Some scientists believe that life came from another planet.
21:55But this may not be the life that turned into us.
21:59Because a radical theory called panspermia
22:02suggests that our ancestors are about to arrive from outer space.
22:08A second wave of rocks pummel the Earth.
22:11And, according to the theory, they're carrying alien hitchhikers.
22:15It's a panspermia.
22:19We don't know.
22:21But I think that the idea that panspermia may have played a role must be considered.
22:26Because a lot of evidence points us in that direction.
22:33The theory that life arrived on Earth from outer space
22:38suggests that our ancestors are about to arrive from outer space.
22:44A lot of evidence points us in that direction.
22:48The story of how alien hitchhikers arrived on Earth starts 4.1 billion years ago.
22:56When the giant outer planets flung Neptune off course
23:00and threw a belt of comets and asteroids.
23:03The giant planets sent a hail of mountain-sized space rocks
23:07towards the inner solar system and the Earth.
23:12It's called the late heavy bombardment.
23:15We're just orbiting the Sun, happy as can be.
23:18And the outer planets are throwing these gigantic objects at us.
23:22And they just kept coming in and kept coming in and kept coming in.
23:28There were giant asteroids and comets raining down on the Earth.
23:31And occasionally even the oceans would be set to boiling.
23:36Even if simple life had started in Earth's oceans,
23:41it would have survived this onslaught.
23:43But the Earth wasn't the only planet in the firing line.
23:47Asteroids and comets also hit Mars.
23:50And back then, it was a very different planet.
23:55Mars is smaller than the Earth. It would have cooled more rapidly.
23:59It could have had a thick atmosphere and oceans of water before the Earth did.
24:04Ancient oceans would have given Mars a head start in the race to foster life.
24:10Perhaps by the time the late heavy bombardment struck,
24:13hardy bacteria had already evolved on the red planet.
24:17We've seen life on Earth that are cryptoendolithic.
24:21So they hide in the rocks and they survive the radiation
24:25and the harsh environment by hiding and thriving inside of that surface.
24:34A giant impact on the surface of early Mars could have thrown rocks
24:39and bacteria high into space.
24:43These are organisms prepackaged, ready to fly.
24:46You could imagine some of them trapped in a rock,
24:49kicked off a planet, flying through space thousands of years later,
24:53landing on another world, popping open and being able to reproduce and grow.
25:03So did a Martian rock seed the Earth with life?
25:09It's possible.
25:12But only if the Martian hitchhikers could survive the long journey through space.
25:21NASA engineer Mujige Kupa knows exactly how hardy bacteria can be.
25:27Because her job is to kill them,
25:30so that no superbacteria from Earth contaminate space missions to other planets.
25:36If we send a rover and it's covered in bacteria,
25:40it could potentially propagate in that environment.
25:45So we're kind of like a bug inspector.
25:48In the ideal case, we would like for every piece of hardware to be sterile.
25:55The reason for this vigilance
25:57is the freakish ability of bacteria to survive in space.
26:02Certain bacteria on Earth, when they experience a stressful environment,
26:07they start forming what we call spores.
26:10And spores, if you imagine a seed,
26:12has all of the genetic information in the middle
26:15and it's protected by numerous layers of defense.
26:18They really seal themselves up in little spaceships
26:21and that would allow them to survive in space.
26:24You could take a spore, put it in space,
26:26bring it back, and it would still be viable.
26:30Spores allow bacteria to stay alive in a dormant state
26:34for incredible lengths of time.
26:37The record on Earth
26:39is a spore that formed before the age of the dinosaurs
26:43and was recently resuscitated after a 250 million year sleep.
26:49You know that spores can survive in theory for millions and millions of years,
26:53but to actually see evidence of a spore being revived
26:57is pretty fantastic.
26:59The final challenge for the Martian hitchhikers
27:03is to survive the impact with Earth's surface.
27:08Planetary scientists simulate this violent event
27:11with high-speed guns loaded with rocks.
27:16Not every bit of the projectile is destroyed
27:19and highly shocked in an impact.
27:21When we do these experiments,
27:23we often find little bits of the projectile
27:25left over in the impact chamber.
27:28If there are bacteria living in that portion of that rock,
27:31they could potentially survive the impact back onto the planet.
27:35The science shows us that panspermia is possible.
27:40But does it take us any closer
27:42to understanding the origins of life?
27:45The fundamental problem with panspermia
27:47is that it's just removing one step of the problem
27:50and putting it someplace else.
27:52We don't know how life originated on Earth.
27:54Now it's going to originate on Mars.
27:57But we don't know how it originated on Mars.
27:59So you still have this basic problem,
28:01and that is, how did life start?
28:04A lot of people say, well, panspermia shouldn't be considered
28:07because it just moves the question somewhere else.
28:10But that may be important,
28:12because I would say that we need two planets
28:15to create what we see on Earth.
28:17One to get it started, and one to carry it on further.
28:22At the moment, we don't know
28:24whether life arrived from space
28:27or rose up from the oceans of the Earth.
28:31All we know is that the next stage of life's journey
28:34is filled with danger.
28:37Because before life can get clever,
28:40it must face oblivion.
28:44Our planet is filled
28:46with a dazzling diversity of life.
28:50Plant life
28:52and animal life.
28:54Simple life.
28:57And complex, intelligent life
28:59like us.
29:02But what is life?
29:05What is life?
29:08What is life?
29:10What is life?
29:13Yet every living thing on Earth
29:15can trace its family tree
29:17back to the same tiny cell
29:19that lived billions of years ago.
29:23All life on Earth
29:25is related to each other.
29:27We share 50% of our DNA
29:29with a banana.
29:31We feel like we're pretty different from a banana,
29:33but when you look at its core,
29:35what its DNA looks like,
29:37it's almost identical.
29:40DNA is the operating code
29:43for the functioning system for life.
29:45It stores the program
29:47that tells cells
29:49how to grow complex structures,
29:51how to generate energy,
29:53and ultimately,
29:55how to make an identical copy
29:57of themselves.
29:59When we look at life,
30:01we tend to focus on
30:03what it's made out of,
30:05and that's important.
30:07It's made out of amino acids
30:09and molecules, etc.
30:12So using the computer words,
30:14it's not the hardware that's so amazing,
30:16it's the software.
30:18The greatest property of DNA
30:20is its ability to change.
30:24Over billions of years,
30:26tiny mistakes in the structure of DNA
30:28have led to the vast diversity
30:30of life we see today.
30:32These mutations can happen
30:34when DNA gets damaged.
30:36The missing section is normally
30:38patched up with a perfect copy.
30:41But from time to time,
30:43a different set of nucleotides
30:45slot into place instead.
30:47Sometimes there are mismatches
30:49that occur,
30:51and these mutations
30:53are sometimes harmful,
30:55but sometimes it could be
30:57a good thing.
30:59Sometimes a random change
31:01might make you process food better,
31:03might make your eyesight
31:05a little bit better,
31:07make you a slightly better hunter,
31:10those are advantageous changes
31:12and they're random.
31:14They don't happen very often,
31:16but they do happen,
31:18and that has led basically
31:20to the way we are now.
31:22Of all the mutations
31:24that led to human life,
31:26the most important
31:28is also one of the earliest.
31:30The jump from simple,
31:32single-celled life
31:34to complex,
31:36multicellular life.
31:39You've got to have
31:41a big enough organism
31:43so that specialization
31:45is enough that some
31:47of the cells,
31:49some of the fraction
31:51of that organism
31:53can just focus on being a brain.
31:55The jump from simple life
31:57to complex life
31:59began around 2.4 billion years ago.
32:01But what was the trigger
32:03for this revolutionary change?
32:05Scientists have boiled it down
32:08to a game-changing mutation
32:10called photosynthesis.
32:12What happened was a mistake.
32:14A mutation led
32:16to a true superpower.
32:20The first organism
32:22to develop this superpower
32:24is called cyanobacteria.
32:26It was green
32:28and able to use sunlight
32:30to create its own food supply.
32:32For the first time,
32:34life had its own internal energy source.
32:36As long as you have sunlight,
32:38you have food.
32:40So you could cut the umbilical cord
32:42and break free
32:44and start to really branch out
32:46into the environments of the Earth.
32:48The cyanobacteria thrived.
32:50But the waste product
32:52of photosynthesis
32:54was oxygen,
32:56a gas that was highly toxic
32:58to almost all other primal life,
33:00a weapon of mass destruction.
33:02At that point,
33:05this was the first time this happened.
33:07And as these things evolved
33:09and flourished,
33:11they started dumping
33:13this basic poison
33:15into the atmosphere.
33:17The oxygen killed off
33:19most of the life on Earth.
33:21But the creatures that survived
33:23evolved to use oxygen
33:25and turbocharge their evolution.
33:27Oxygen is so dangerous
33:29because it's so reactive,
33:31but that makes it a very good fuel.
33:33A tiny percentage of life that wasn't killed
33:35by the poisonous gas oxygen
33:37all of a sudden could speed up
33:39and had a more efficient fuel to use.
33:41And more energy means more complex molecules,
33:43more complex chemistry,
33:45more complex biology.
33:47And that meant that these creatures
33:49could evolve more rapidly.
33:51Boosted by oxygen,
33:53some single cells evolved
33:55to do something they hadn't done before.
33:57They joined forces.
33:59Single-celled microorganisms
34:01really were smart when they knew
34:03to cluster together
34:05because it allowed them to have protection
34:07and work kind of as a community.
34:09Different cells within these communities
34:11started to specialise
34:13in different tasks.
34:15Eventually,
34:17the communities started to function
34:19as a single organism.
34:21The stage was set
34:23for the next superpower,
34:25multicellular life.
34:27But a second global catastrophe
34:29was coming
34:31because, in the background,
34:33cyanobacteria populations
34:35were still exploding.
34:39As they released the oxygen
34:41as they grew,
34:43it would have changed the chemistry
34:45of the entire planet.
34:49As oxygen filled the air,
34:51it reacted with the early atmosphere,
34:53removing greenhouse gases
34:55such as methane.
34:57The result
34:59was a rapid cooling of the Earth's climate.
35:01And this, we think,
35:03would have tipped the climate
35:05of the entire planet
35:07to a very, very cold,
35:09kind of glaciated world,
35:11what we call the Snowball Earth.
35:15And it was probably
35:17the first climate catastrophe
35:19that happened after life originated on Earth.
35:21Snowball Earth
35:23came very close to wiping all life
35:25off the surface of our planet.
35:27But some creatures
35:29must have made it through,
35:31otherwise we wouldn't be here today.
35:35Geothermal hot springs,
35:37like this one in Iceland,
35:39offer a clue as to how our tiny ancestors
35:41managed to survive this trial by ice.
35:45This temperature's shooting up.
35:47160, 170,
35:49180,
35:51190,
35:53over 200 degrees Fahrenheit.
35:55That's very, very hot.
35:57That's practically the boiling point
35:59of the water.
36:01And you can see it's kind of churning away
36:03like cooking soup or something in the kitchen at home.
36:07The heat source for hot springs like these
36:09is buried deep within the molten core
36:11of the Earth.
36:15Radioactive metals sank here
36:17during the formation of the Earth,
36:19slowly releasing heat
36:21into the rocks that sit below the surface
36:23of our planet.
36:25Where the Earth's crust
36:27is thin, rainwater
36:29can seep down onto these hot rocks
36:31and shoot back up
36:33at near boiling point.
36:35Warm pools like these
36:37would have kept on bubbling all the way through
36:39Snowball Earth.
36:43What probably would have helped us
36:45in that process of survival
36:47were regions like this.
36:49There still would have been volcanic activity
36:51and geothermal hot spots,
36:53and they would have thawed out the ice
36:55and provided oases of warmth
36:57where life has an opportunity to cling on.
36:59So maybe it was less of a
37:01Snowball Earth
37:03and more of a slush ball.
37:05Maybe there were periods and regions
37:07around the equator and around hot spots
37:09where life was able to persist.
37:13Snowball Earth lasts for 200 million years.
37:17Eventually,
37:19volcanoes released enough greenhouse gases
37:21for the climate to recover.
37:23And the organisms that survived
37:25inherited a warm,
37:27oxygenated world
37:29perfect for multicellular life.
37:31Multicellularity really booms,
37:33and it seems to coincide
37:35with the rise in oxygen.
37:39Over the next 500 million years,
37:41oxygen levels continue to rise,
37:43and life grew bigger
37:45and more complex.
37:49Most of the major animal groups
37:51we see today evolved.
37:53Fish turn into reptiles.
37:57Reptiles turn into small mammals
37:59and then primates.
38:01Finally,
38:03just 200,000 years ago,
38:05the first humans walked the Earth.
38:09Beings with the capacity
38:11for intelligent thought.
38:13There are a lot of landmarks in evolution.
38:15There aren't very many.
38:17I would just have three.
38:19The origin of life,
38:21the rise of complex life
38:23associated with oxygen,
38:25and the rise of intelligence.
38:27That's it.
38:29To me, that's the story of life on Earth.
38:31It started, it got complex,
38:33and it got smart.
38:35Now scientists are investigating
38:37whether the same process of evolution
38:39could have happened elsewhere.
38:41Now, is there intelligent life?
38:43That's a much more difficult question.
38:47One way to answer it
38:49is to look at the key factors
38:51that made our evolution possible
38:53and see if they exist elsewhere.
38:55By studying the light
38:57from distant dust clouds,
38:59astronomers now know
39:01that the building blocks for life
39:03are common throughout the galaxy.
39:05And they've detected over 1,000
39:07potential planetary homes
39:09and life around nearby stars.
39:11The stage, for simple life at least,
39:13seems virtually infinite.
39:17But for complex, multicellular life,
39:19you need something else,
39:21an oxygen-rich atmosphere.
39:25Is there oxygen on these worlds?
39:27That's the question
39:29I want to live to see the answer to.
39:31And if the answer for any of them is yes,
39:33that's phenomenal.
39:35That is really an important milestone
39:37in our understanding
39:39of life in the universe.
39:41NASA is developing a new generation
39:43of telescopes
39:45to find planets around nearby stars
39:47and scan for oxygen-rich atmospheres.
39:51But a recent surprise result
39:53from the planet next door
39:55suggests oxygen-rich worlds
39:57may be much more common
39:59than we thought.
40:02I think we can do right here.
40:06Nina Lanza works with NASA
40:08on the Mars Curiosity rover.
40:11She's interested in a mysterious
40:13black glaze that appears
40:15to be present on both Mars
40:17and the Earth.
40:19So what we're looking at here
40:21is called rock varnish,
40:23and this is a coating
40:25on the surface of the rock
40:27that is very high in manganese oxides.
40:32Living cells on Earth
40:34contain manganese.
40:36These dark deposits
40:38are thought to have been formed
40:40when this manganese leached
40:42out of dead bacteria.
40:44The manganese then reacted
40:46with oxygen in the air
40:48and became fixed to the rock.
40:50Nina wanted to understand
40:52the chemistry of similar-looking
40:54stains on Mars.
40:56So, in 2014,
40:58she requested the Mars Curiosity rover
41:00to fire at a set of dark rocks
41:02with its ChemCam laser.
41:06Wherever you zap the rock,
41:08it vaporises a little bit of material,
41:10and so if we keep shooting the rock
41:12in that one place,
41:14then we can find out the composition
41:16through the coating, if there is one.
41:25There was this one sample
41:27that had such a big peak
41:29that we noticed it right away,
41:31and we were like, this has to be a mistake.
41:33We need to check our data
41:35to make sure we haven't miscalibrated it,
41:37and absolutely not.
41:39We looked at the raw data,
41:41we recalibrated it,
41:43and it was still a huge amount
41:45of manganese.
41:47The surprise result suggests
41:49life may once have thrived
41:51on Martian rocks
41:53inside an oxygen-rich atmosphere.
41:55Even if the manganese
41:57came from another source,
41:59the dark stains would have still required
42:01atmospheric oxygen to fix them
42:03to the rocks.
42:05So, finding a coating
42:07like this on Mars,
42:09or even just a layer made of a similar composition,
42:11opens up the possibility
42:13that there was oxygen in the Martian atmosphere
42:15sometime in the past.
42:19Mars lost its atmosphere
42:21billions of years ago.
42:23But the possibility
42:25it once had oxygen
42:27is significant.
42:29Because,
42:31if two planets in the same solar system
42:33can both have all the ingredients
42:35needed to develop complex life,
42:39then the odds on there being
42:41more intelligent life out there
42:43look pretty good.
42:49When we look at the story of life,
42:51it seems like
42:53the universe started off with hydrogen
42:55and has now ended up with intelligence,
42:57human beings. Well, that's a wonderful story.
42:59Are we the only chapter
43:01in that book, though? That's the question.
43:05Whether or not there's a person
43:07in some faraway galaxy
43:09having the same thoughts as I am,
43:11I'm not sure.
43:13It's hard to say no,
43:15because this universe is so large.
43:17We are a collection of atoms
43:19that understands that it's a collection of atoms.
43:21That's amazing!
43:23This is the universe knowing that it's the universe.
43:25So I think it's really important
43:27that we figure out how that's possible.
43:33I actually have a bottle of very nice champagne
43:35chilling in my refrigerator.
43:37I think we're going to find evidence
43:39of life on another planet sometime in my lifetime.
43:41I'm ready to celebrate.
43:47NASA Jet Propulsion Laboratory, California Institute of Technology