- 1 day ago
Discover how scientists are unearthing evidence from lunar rocks and ancient impact craters, revealing that the very objects known for extinguishing life might ...
探讨巨大的小行星撞击对于地球生命的诞生是否确实至关重要。
探讨巨大的小行星撞击对于地球生命的诞生是否确实至关重要。
Category
📚
LearningTranscript
00:00Viewers like you make this program possible.
00:03Support your local PBS station.
00:12Earth is a living planet.
00:18But it wasn't always that way.
00:22Life had a beginning.
00:25When and how did life emerge on this planet?
00:28What environments did it live on throughout Earth's history?
00:34These are some of our planet's greatest mysteries.
00:43For a long time,
00:45scientists thought life could not have appeared very early in Earth's history
00:50when the planet was under heavy bombardment by asteroids.
00:55A tremendous number of impacts.
00:57Even a large one.
00:58Imagine an object the size of the moon that could have collided with the Earth.
01:07But now, scientists are finding new clues.
01:11In ancient rocks.
01:13On the surface of the moon.
01:15Even on space rocks hundreds of millions of miles away.
01:20And inside craters made by massive asteroid impacts.
01:26And they're wondering.
01:28Instead of preventing life from starting.
01:31Could violent impacts like these actually be essential?
01:37Asteroids could have delivered the basic chemical building blocks of life to Earth.
01:43Leading some scientists to ask.
01:46Could asteroids be the spark of life?
01:49Right now.
01:50On NOVA.
02:14On NOVA.
02:19In
02:21mountains in South Africa here lies some of the oldest and rarest rocks visible
02:27on the surface of our planet and here geologists Nadia Drabun and Puma Lele
02:34Masha Lee are searching for evidence of the conditions on the early earth to
02:39help solve the mystery of how life got started so we'll be going right here
02:46right where you see the purple meet the orange right near the river yeah
02:56when someone comes onto these mountains they think oh wow that's a really
03:00beautiful scenery and really gorgeous however when I come here I really start
03:05seeing earth history unfolding layer by layer some of the Barberton Macandre rocks are as
03:11old as 3.6 billion years they've only survived this long because the mountain
03:18range sits on a relatively stable part of the earth's crust they date back to a
03:27geological eon called the Archean earth itself had only formed about 900 million years before
03:41the Archean world was alien there was no breathable oxygen erupting volcanoes poured
03:49vast quantities of greenhouse gases into the atmosphere the Sun was a lot weaker than it
03:59is today but these gases kept the planet warm warm enough for liquid water on its surface in fact some
04:09of the
04:10minerals found in Archean rocks suggest the planet was already an ocean world so there
04:17was water was there also life these Archean rocks are some of the best preserved in the world could they
04:35contain signs of ancient life forms in this vast landscape Nadia thinks she may have found some traces
04:48when you look at these rocks here some of these layers look just really black but what I'm
04:53seeing here is really the remains of life back then people have taken a really close look through the
04:59microscope and what they're finding is remains of single-cellular organisms preserved within the rock
05:09what did these microbes look like was this the first life on earth
05:18far from the mountains of Barbiton in the city of Orléans France geologist Francis Westall examines ancient rock
05:26samples hunting for signs of life we have here in front of me a collection of rocks from Barbiton's in
05:38South Africa and also from the Pilbara in Australia these rocks are more than 3 billion years old in these
05:47rocks I have found traces of fossil microbial life these rocky outcrops in the arid regions of the
05:58Pilbara in the northwest of Australia are as ancient as those in the Barbiton Maconjoa mountains
06:08rocks from both locations have given Francis and her colleagues some of the best evidence yet of what life may
06:15have been like in the Archean Eon over 3 billion years ago to detect ancient life forms Francis uses a
06:28scanning
06:29electron microscope a concentrated beam of electrons scans the sample and interacts with atoms on the
06:37surface creating signals that can be translated into highly magnified images
06:44but this rock is not a good conductor of electrons so it's coated with a thin layer of a material
06:51that
06:51is gold in a 3.3 billion year old sample from Barbiton Francis identifies what many believe are fossilized
07:04life forms here you can see an individual filament here as well Francis thinks each of these thread-like
07:13structures is a cell about 70 times thinner than a human hair how do we know that that they're microbial
07:21fossils and not something else that's got nothing to do with microbes minerals for instance one method is
07:28to compare them to micro fossils of modern bacteria that Francis actually made in her lab
07:36she entombed living microbes in silica in nature silica can fossilize an ancient organism by
07:44penetrating and coating its internal structure in an extremely old rock sample from the Pilbara in Australia
07:54Francis finds a shape that looks like one of her modern silica coated microbes
08:02chemical analysis reveals signatures of what could be organic molecules which means this might have been
08:10an ancient life form I've been able to reveal traces of single cells we can see cell division
08:24we can see also here cell division these are cells that are preserved in a rock nearly three and a
08:32half
08:32billion years old and they are exquisitely preserved they could be some of the oldest micro fossils so far
08:41found on earth traces of a variety of single-celled life forms that lived in different environments over
08:49over three billion years ago have been found in Barberton and the Pilbara
08:56even though they were single-celled they came in a variety of shapes and so this could not have been
09:04the first life
09:07life was extremely diversified already by three and a half billion years ago which tells me that it must have
09:14emerged a lot
09:15earlier than we originally thought possibly between 4.3 and 4.2 billion years ago
09:26that would place the origins of life within the most mysterious and inhospitable eon in Earth's history
09:35the Hadean
09:39this was a time even before the Archean
09:46Archean rocks may be extremely rare but Earth's Hadean rocks are nearly unheard of because most rocks
09:55on Earth eventually get destroyed eroded away or melted down for most of our planet's history Earth's crust has been
10:05broken into plates
10:07sometimes when two plates collide one will slide under the other pushing the surface rocks down into the mantle
10:15it's as though Earth is swallowing its past
10:23direct evidence of the Hadean may be long gone
10:26but what we do know is that over four and a half billion years ago our planet had just formed
10:33from dust and rock particles
10:35that circled our young Sun so its surface was unstable
10:42scientists named the Eon after Hades because they believed it must have been a hellish place covered with molten lava
10:50from erupting volcanoes
10:53on top of that giant asteroids left over from the formation of the solar system pummeled the planet
11:06could life have emerged and survived in such hellish conditions
11:14to find the answer scientists must first know what life actually is
11:21the answer is
11:24Karen Rogers is an astrobiologist and geochemist
11:32Karen and her team study the origins of life
11:39at some point in Earth's history
11:41there wasn't life
11:44and there had to from that entire planet
11:47there was a planet that was abiotic
11:48that had no life on it
11:50there was a chemistry or probably a series of chemistries and reactions that were intertwined
11:56that eventually came into life
12:01scientists don't yet know the exact chemistry that created life
12:06but they do know its building blocks
12:09molecules containing elements like carbon hydrogen nitrogen and oxygen
12:14which are found all over the solar system
12:18can join to form organic molecules including sugars and amino acids
12:25these bond to make even bigger molecules
12:29amino acids form proteins vital for the functions of a cell
12:35how do we make the amino acids that turn into proteins how are the sugars
12:41that form the backbone of dna and rna originally synthesized
12:46so life has all of these ingredients and they need to come together just right to eventually get to life
12:52as we know it
12:55the recipe required a source of energy and one of life's most essential ingredients
13:02liquid water
13:04so if life did emerge 4.3 billion years ago
13:09then this ancient extremely hot planet had to also be a wet planet
13:17the rocks that could prove that might be long gone
13:20but for years scientists have been gathering clues from tiny ancient mineral crystals
13:32when rocks erode some minerals can survive and get incorporated into new rocks
13:46in 2018
13:47in 2018 here in the barbiton macandrua mountain range
13:50nadia drabon and her team found grains of a type of mineral known to be the earth's oldest surviving material
13:58zircon
14:02zircon
14:03zircon is an extremely tough little crystal
14:06once it forms it's very hard to break down
14:10zircon can withstand billions of years of weathering
14:13so it retains evidence about the rock in which it originally formed
14:20and that's why the zircons nadia and her team discovered on this mountain are so special
14:30so this here is actually my favorite rock in the entire barbiton greenstone belt
14:34that is because you find zircon about 200 million years older than the oldest rock on earth
14:42which means nadia had discovered some of the rarest zircons on the planet
14:47up to 4.2 billion years old from the hadian
14:53chemical analysis of these along with even older hadian zircons found in australia in the 1980s
15:00revealed that they had formed in the presence of a very special ingredient
15:11by about 4.3 billion years ago we've got evidence for liquid water preserved within these zircons
15:20the presence of water in the hadian 4.3 billion years ago is crucial because water is one of the
15:28key
15:28ingredients for life and life as we know it could not have emerged without it
15:36that began to paint a picture of what the hadian landscape was like
15:44it was not exactly the hellish place scientists once thought it was
15:53we had emergent land but maybe not a lot of it and we had an ocean covering most of the
16:02planet
16:06for oceans to exist the planet's crust must have cooled much faster than scientists once thought
16:15but where did the water come from
16:18some scientists believe it was delivered by asteroids and comets
16:23but earth may also have been born with water trapped deep inside the mantle
16:28and volcanic activity delivered it to the surface as steam
16:35and in addition we were regularly getting bombarded with meteorites and asteroids
16:41and so they came in one after another after another
16:47did life have to wait for a lull in the bombardments before it could spark
16:53or was it hardy enough to emerge despite the chaos snuffed out by an impact in one place
17:02only to re-emerge in another
17:13so far no direct evidence of these early asteroid impacts has been found on earth
17:22there may be traces of impacts that happened around three and a half billion years ago
17:27back in the barbiton macandrual mountains
17:31while any craters would have been eroded away much tinier clues can survive
17:39i just found one
17:43these things are so difficult to find like in this whole package of rocks
17:47these are the few that are well preserved
17:53this tiny circle is a spheriol spheriols can form as a direct result of massive asteroid impacts
18:05when you have a giant impactor so think about 10 kilometers in diameter or bigger when that smashes
18:11into earth you actually have so much energy that is going to form a rock vapor cloud that it's going
18:16to be ejected out of the crater at speeds of up to 40 000 miles per hour
18:23this rock vapor cloud is going to start condensing to form these spheriols
18:27that are going to rain out and blanket the entire globe
18:32without visible craters these scattered spheriols may be the only remaining evidence of an impact
18:38so it's impossible to know exactly where on earth the asteroid hit
18:50as the spheriols rain down they form layers the thicker the layer the larger the original impact
18:58and the spheriol layer that nadia and pumilele locate is very thick almost eight inches deep
19:06so the asteroid that created it was probably more than 20 miles across
19:13for the impact energy what we actually think about is the mass and that would have been
19:1750 to 200 times bigger than that of the impactor that killed the dinosaurs
19:27these sharks tell the whole story from before the impact happened to the actual impact event and
19:32then tell the environment and life responded before the impact happened about 3.26 billion years ago
19:38here at this location we would have been standing on the sea floor on the shallow sea floor and there
19:44was a little bit of life present but not too much and then all of a sudden this is changing
19:51really dramatically
19:57the asteroid hit the ocean triggering an enormous tsunami that swept across the globe
20:04evidence of the big wave is in the rocks
20:10and that's what we see here these big chunks that were ripped up from the sea floor right below
20:19what effects did the tsunami have on the simple life that may have lived at the time
20:25nadia finds clues and sediments that formed not long after the impact
20:30the rocks are red an indication of iron and a central nutrient for life
20:38what we think is that the tsunami that was sweeping by was bringing iron-rich
20:43waters from the deep oceans to the surface
20:48a closer look at the iron-bearing rocks reveals another surprise
20:55signs that life bounced back very quickly after the impact how could this happen so what we think
21:04we see in these rocks that these microbes are starting to respond to that increase in nutrients
21:09and iron and are actually starting to bloom
21:17when people think about giant meteorite impacts they first think about the extinction of the dinosaurs
21:23what we think what we are seeing here is that life was not only able to survive these really
21:28disastrous consequences for the environment life was actually able to thrive
21:34so far evidence of several giant impacts that happened between 3.5
21:39and 3.2 billion years ago has been found in these mountains
21:45but what was happening earlier during the hadian 4.3 billion years ago when some scientists think the
21:53very first life emerged
21:58traces of that time on earth are long gone but there's another place that can tell the story
22:05the moon whose surface has retained the kinds of scars that once covered earth
22:12we don't have any surviving remnants of that hadian earth and so it's easy i think to imagine that that
22:20surface was not cratered but the moon actually tells us otherwise zero zero five seven two
22:31david kring is an astrobiologist at the lunar and planetary institute in houston
22:37he studies the surface of the moon to learn about the early earth
22:48in the early and mid-20th century scientists debated the origin of the circular structures
22:55on the lunar surface were they huge volcanoes or were they impact craters ignition sequence start
23:05almost immediately the apollo 11 mission answered this question with the samples that were collected and
23:12brought back to earth it became evident that nearly all of those circular features must have been
23:18generated by impacting asteroids and comets it was a turning point when scientists realized that violent
23:27asteroid impacts could reshape the surface of a planet including our own
23:35the craters on the moon were beautifully preserved
23:39undisturbed by erosion or plate tectonics like we have here on earth
23:47scientists started to count them
23:50the older a planetary surface the more time there has been for it to be hit by these impacting asteroids
24:01and therefore the greater the number of craters
24:10thousands of craters larger than a mile wide have been counted so far
24:17when the moon rocks from some of the craters were dated scientists were in for a surprise
24:26in most cases the samples that were returned by the apollo astronauts had very very old ages
24:35in what we now call the hadian of earth history indicating that there was
24:41early in solar system history an intense period of bombardment
24:48if the moon suffered this many violent impacts how many and how large were the asteroids that hit the
24:54early earth how frequently did they impact and how could they affect the emergence of life
25:02planetary scientist simona markey has been piecing the story together
25:10so
25:19there's one single process that's very important to me that i find it very fascinating and that is the
25:25process of collisions
25:29everywhere you look everywhere in the solar system there is a solid surface you'll find that there
25:34craters the craters are a reminder of our solar systems formation around 4.56
25:44billion years ago it began as a disk of dust and gas in orbit around the young
25:53Sun the solid materials collided and clumped together to gradually form the
26:07rocky planets
26:09as a result of the formation of the earth there were still lots of the breeze and
26:13asteroids and and others molar objects flying around the Sun those objects kept
26:20colliding with the surface of the earth
26:29about four and a half billion years ago a single object the size of Mars or even
26:36bigger may have crashed into the young earth this high-resolution simulation
26:43reveals how the collision flung enough molten and vaporized debris into space
26:48to create the moon
26:53I'm trying to understand the early evolution of the earth and the effects of all
26:58those impacts that were taking place during the idea on earth so we do this by
27:03building models one of the most important sources of data comes from NASA's lunar
27:10reconnaissance mission this robotic spacecraft has made a 3d map of the moon's surface at extremely high
27:21resolution the first thing that we do is to look at the surface of the moon it is much
27:29older than the surface of the earth the surface of the moon is full of impact craters all the impact
27:35craters and so we can use that information by mapping how many there are and their
27:40sizes and their ages and that will provide us the primary information that
27:45we need to build our models it took an international team decades to collect the
27:51data but they finally created a computer model that took what happened on the moon
27:57during the Hadean and simulated the asteroids that would have hit the earth during the same stretch
28:02of time and the outcome of that first modeling was staggering we are seeing the entire surface of
28:17the earth that is strongly affected by impacts every single circle that you see here is is an impact
28:32there's a collision the prediction was that there were a tremendous number of impacts even large
28:38one imagine an object the size of the moon that could have collided with the earth that would have
28:51basically wiped out almost entirely perhaps the oceans vaporized the oceans and melted a large
28:57portion of the crust of the earth this series of apocalyptic bombardments might look like it created a
29:05chaotic hellscape on earth but fossil evidence suggests that life did emerge during the Hadean so even during
29:15asteroid impacts there must have been enough habitable conditions somewhere on the planet for life to get a
29:21foothold if life started on air around perhaps 4.2 billion years ago or there about then the question is
29:32how
29:32that was connected to the impacts that were taking place at the same time the origins of life community
29:41rarely thought about impacts as part of the origin story it's really hard to not think about them we
29:50really had to change our our sort of frame of mind and I certainly did to investigate what effects the
29:59asteroid impacts had on the emergence of life Karen Rogers is recreating the conditions of the Hadean earth in her
30:06lab
30:10some ways the early earth was a big experimental laboratory doing prebiotic chemistry
30:22we can do experiments that were similar to what the early earth was doing and hopefully discover the
30:29chemistry that eventually led to life Karen's team can create tiny Hadean environments with the same temperatures pressures gases water
30:42composition and types of rocks that may have existed at the time echoing the places which may
30:54have had the chemistry needed for simple molecules to join and eventually lead to the first cell so what we
31:04think about the origins of life there are a few different ideas that have been around for a while that
31:09people
31:09have been studying for quite some time one of them is a hydrothermal system origin of life these are hot
31:19water systems heated by volcanic activity one of the really special things about hydrothermal
31:25systems is that they can provide energy either for life or maybe the chemistry that allows life to emerge
31:34hydrothermal systems can appear on land where magma pushes towards the surface creating hot springs and geysers like the ones
31:43at
31:43yellowstone and in the deep sea here the cold sea water descends into fractures in the rock and interacts with
31:51the minerals
31:53heated by magma it re-emerges through chimney-like structures now enriched with the types of organic molecules necessary for
32:01life
32:07we have really hot hydrothermal fluid coming out of a chimney it's full of metals and it's mixing with seawater
32:17and so when those two fluids come together they could also provide energy to do organic chemistry that might lead
32:24to life
32:29so did the very first primitive cells emerge and survive in hydrothermal systems and if so where on land
32:37in the deep sea or somewhere else was that even possible under a steady barrage of asteroids
32:49when we think about life surviving on the earth we think about things that allow it to thrive
32:54and things that might actually destroy it and probably one of the most prominent
32:59sort of events that destroyed life was the impact that killed the dinosaurs
33:0966 million years ago long after the haydian ended a space rock bigger than mount everest hurtled toward our planet
33:19it was a moment that would change the evolution of life on earth a vivid reminder of the havoc
33:27and devastation that an asteroid impact can wreak
33:33that one impact alone wiped out 75 percent of earth species after it hit the yucatan peninsula
33:51the chick's lube impact crater was produced by an asteroid it hit with a energy equivalent to 100 million
34:00megatons of energy that's a tremendous blast
34:10david kring has studied rocks from beneath the chick's lube impact crater
34:18looking at tiny slices of the rock under a microscope
34:24he found quartz crystals that had been shocked and deformed by the intense pressure generated by the impact
34:37but he also saw something much more surprising minerals like anhydrite which are produced hydrothermally
34:45in the presence of very hot water
34:51so this is evidence that the impact event heated the earth's crust
34:57heating the water within the earth's crust and then generated a vast circulating hydrothermal system
35:09this system would have been similar to volcanically driven hydrothermal systems where some scientists
35:16believe life first emerged but this one was much larger
35:22as david probed further he found something else locked inside the minerals
35:32signs that ancient microbes were living in chick's lube's hydrothermal system just after the impact
35:42we now have evidence that it hosted a microbial ecosystem they provided the habitat in which
35:50these organisms thrived and grew throughout the crust of the earth beneath the floor of the chick's
35:58of impact crater
36:03and it wasn't just chick's a loop as scientists surveyed the 200 known impact craters and structures
36:10on earth they discovered that about a third of them show signs of the same type of hydrothermal activity
36:18and so we began to realize that this was a common process that would have occurred
36:24in impact craters throughout the hadian period
36:29what did these ancient hydrothermal systems look like
36:34there could be clues inside one of earth's best preserved craters
36:38about 15 million years ago an asteroid hit southern germany making an almost 16 mile wide crater known as ries
36:51the impactor was about the same size as a medieval town called nurdlingen built inside the crater which
36:59is nearly invisible today even from the highest tower the rim is hard to make out
37:06it's hard to make out of it but human-made quarries have exposed the secrets that lie beneath the crater
37:14all along the rock walls excavation has exposed strange vertical pipe-like structures
37:26planetary geologist livio tornabene is at reese crater to learn more about these formations
37:31which are visible as rust-colored rock
37:41it's really bounding this pipe structure
37:44i mean it looks like it disappears but it probably goes into the rock
37:48you probably have to see this in three dimensions and it would be sort of
37:53branching out and trying to find the quickest route up to the surface
37:59after decades of research scientists believe they know how these pipes were formed
38:06here we're we're actually below the surface of the of the deposit uh as it would have been 15 million
38:13years
38:13ago it's really well preserved and for a crater this size it would have produced a lot of melt
38:21that would have been superheated
38:24the heat from the melt released water from the rock and turned it into gas
38:32the energy of the escaping steam forged pathways up through the hardening rock creating what scientists
38:38call degassing pipes
38:46the darker color of the pipes is evidence that liquids and gases once flowed through them
38:56we know that there was fluid here running through these rocks there was heat there were
39:02available nutrients and that is definitely the combination that you want to look for
39:08when looking for life here on earth or on mars or elsewhere in the solar system
39:17these degassing pipes were like the plumbing of a vast hydrothermal system
39:22with every excavation more are exposed
39:27so how large were the hydrothermal systems that formed during the haydean
39:33the chick's a lube crater may help scientists in their estimates
39:39so chick's lube is a good model for some of the smaller impact events that occurred during the haydean
39:48at the southwest research institute geologist amanda alexander runs one of the latest chick's a lube models
39:58the blue green color shows the areas where the impact would have fractured the rock allowing water
40:03to flow through creating a hydrothermal system it was much bigger than scientists thought
40:13about 10 times larger than was previously expected and about 100 times larger than we think is the
40:19current yellowstone hydrothermal system
40:23and this astonishing estimate is for only one crater
40:30so the chick's a lube impactor was about 14 kilometers in size but the impacts that were
40:35happening on the haydean were much larger and much more frequent
40:43impacts like these would have been occurring over the half a billion year duration of the haydean
40:54so at some point vast hydrothermal systems might have covered much of the planet
41:00all of this research is leading to a remarkable idea it's looking more and more like asteroid impacts
41:08were double-edged swords while they were certainly bringers of chaos and destruction they might have
41:15created ideal conditions for life
41:20but what about the raw ingredients how can we know if they were present at asteroid impact sites
41:34that are constantly bombarding the earth
41:34danny glavin is an astrobiologist at nasa's goddard space flight center near washington dc
41:42he's been looking for the ingredients of life in space rocks
41:48meteorites are really fascinating objects these are fragments of asteroid material that are constantly
41:55bombarding the earth something like 5000 metric tons of material is falling to the earth each year
42:04in 1969 what would become one of the world's most studied meteorites fell to earth in southeast australia
42:12it was named murchison after a nearby town
42:17this meteorite was a treasure trove containing hundreds of amino acids and other fundamental building blocks of life
42:32the way we extract these meteorite samples to look for the chemical building blocks of life is we
42:37start with a small chunk maybe the size of a sugar cube start chopping it up grinding it up we
42:42make kind
42:43of a meteorite flower and then we take that powder and we put it in a test tube with water
42:49to extract it so
42:51we're making kind of a meteorite tea if you will we take the liquid water we purify it through several
42:58steps we want to remove the salts from the extract so that we can really focus on the amino acids
43:05and
43:05detecting them and then the final step is we inject that liquid into a mass spectrometer to separate out
43:12the individual amino acid peaks and identify them by name
43:18but there's a problem with studying meteorites that have made their way to earth's surface
43:26one of the challenges with meteorites that as soon as they hit the atmosphere
43:31and hit the ground they they immediately become contaminated
43:37liftoff of osiris-rex to boldly go to the asteroid bedroom and back
43:43we really do need to go to space to go to asteroids and bring back pristine samples
43:49that have never seen the earth's biosphere
43:55in 2016 nasa's osiris-rex mission headed to the asteroid venu
44:04venu is slightly taller than the empire state building
44:07and from a distance it looked like it would have had the same kind of rocky makeup as meteorites like
44:13murchison
44:20in october 2020 osiris-rex bounced off benu and grabbed a sample of its surface material
44:29we fired the nitrogen to collect the sample there was a huge plume of material when we imaged the
44:35sample collector we saw there was a bounty of material from asteroid banner in the collector so
44:41we had done our job
44:44it took just under three years for the sample to be returned to earth
44:49altogether the mission brought back about 122 grams the largest sample ever collected from an asteroid
44:59the precious space dust was divided up and sent to labs around the world for analysis
45:07dani's lab got about five grams so you're looking at a very tiny speck of benu
45:15even in a particle as small as a half a millimeter we can extract these samples
45:20and look for amino acids and other chemical building blocks of life
45:26benu was rich in carbon the element of life 14 of the 20 amino acids found in life on earth
45:34were also detected along with all of the chemical bases of our genetic code
45:44which begs the question what would happen if an asteroid that created a vast hydrothermal system
45:50on impact also delivered the building blocks of life directly to that site
46:01could those building blocks survive such a violent destructive event
46:12nobody really knew what happened to these organic compounds once they got delivered
46:17and we do know that when impactors hit the earth they create hydrothermal systems and nobody asked
46:24gee what happens to those organic compounds in those hydrothermal systems so we did lots and lots of experiments
46:36mary herrero perez conducts the experiments under early earth conditions
46:49mary takes a mineral thought to be on the hadian earth and found in impact craters today
46:59to this she adds a mixture of simulated hadian water and soluble organic compounds including amino acids
47:06like those present in some meteorites
47:16she then places these ingredients into a chamber
47:19where they're exposed to the conditions typical of a hydrothermal system made by an impact
47:24highway habitat it requires liquid water energy and heat
47:28and heat
47:37hybrid thermal systems made by impacts cool over a long period of time
47:44so the experiments are conducted using a range of temperatures
47:56Mary conducted hundreds of these trials, each lasting seven days.
48:07I remember the first time that I looked at all the experiments that needed to be done,
48:10it was 180, and I thought that that was a lot.
48:13But the actual thing is I ended up doing probably more than double or triple that.
48:27After the tests, Mary used a nuclear magnetic resonance spectrometer
48:32to help identify the structures of any molecules that may have formed during the experiment.
48:40The results were beyond surprising.
48:45The first time I saw the results of a successful experiment, I did not believe what I was seeing.
48:51I thought I had done it wrong.
48:53And then I spoke with Karen and we could understand that there was more complex chemistry happening that we envisioned.
49:02Our question was, did these molecules start to react with each other as they went through this impact-generated hydrothermal
49:10system?
49:10There was always a possibility that they just broke down and never led to life.
49:15But what we found is instead, these molecules actually got together and made new and bigger molecules.
49:24Now, we're still trying to figure out what those new and bigger molecules are, but as you make bigger molecules,
49:31you really are pushing in the right direction to build the complex chemistry that could eventually lead to life.
49:45Exactly where and when that complex chemistry made the leap to biology and life first emerged remains a mystery.
49:53Many scientists still believe that hydrothermal systems created by volcanic activity deep in the sea, or on the surface, are
50:03the best candidates.
50:05But some scientists are rethinking what role asteroid impacts might have played in the origins of life.
50:15We always think about asteroids colliding on the surface of the Earth as a very negative event.
50:22Maybe that's what we needed in order to get the chemistry necessary for life to form.
50:30Those very same impact events were perfect crucibles for the origin and early evolution of life.
50:39They really generated an environmental life that allowed it to evolve to what it is today.
50:46Many lines of evidence have led to a remarkable hypothesis that life might have begun as a result of those
50:54huge impacts rather than in spite of them.
50:59Perhaps over 4 billion years ago, a space rock laden with the building blocks of life hit the Earth, creating
51:07a vast hydrothermal system.
51:09One of hundreds of thousands that covered our planet.
51:13Each one with the water, the energy, and the ingredients to brew the chemistry of life.
51:22And these asteroid impacts were happening all over the solar system.
51:31On Mars, the remains of hydrothermal systems have been discovered beneath many asteroid impact craters.
51:39And inside one 4 billion-year-old crater, NASA's Perseverance rover has collected the most tantalizing evidence yet of potential
51:49microbial life on the Red Planet.
51:55Who knows what discoveries may await on distant rocky surfaces elsewhere in our own solar system and beyond that might
52:05finally reveal once and for all that we are not alone.
52:34We'll stay next far.
52:37We'll need to get started next time in the comments today.
53:07Transcription by CastingWords
Comments