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00:00Our neighborhood is a cosmic pinball machine
00:04Rock piles as big as cities plow into the planets and leave mystery in their wake. Everything we see in the solar system
00:10These are our witnesses. We just have to get them in the park. If we don't we could be one of the next victims of a collision in our solar system
00:30Our solar system is more than just eight planets and over 170 moons revolving around our Sun
00:38Lurking in the vast empty space between these giant bodies are smaller bodies
00:44But small is relative these asteroids and comets that share our neighborhood
00:49Have been plowing into the planets since the solar system formed
00:53We have mapped the planets poured over the data and everywhere we look in our solar system
00:59We find impact scars the evidence points to one thing
01:04When we gaze up at our seemingly tranquil skies, they are anything, but
01:10Our solar system
01:12Is a dangerous place
01:15Case in point our nearest celestial companion is a crime scene spattered with evidence of violent impacts from the past
01:24When we look up at the moon in the night sky it's a reassuring presence
01:29It lights our nights
01:32Pulls our oceans tides and marks our days with its phases
01:37But the craters on the moon are anything, but reassuring
01:41Like the scars on a prizefighter's face. They have a long and violent story to tell us
01:47About epic battles in our neighborhood
01:50The moon really is sort of the ancient textbook from which we can read the history of the solar system
01:59The moon's textbook lesson began four and a half billion years ago with its apocalyptic birth
02:06The moon is the byproduct of a catastrophic collision
02:10By something that hit us a
02:12A planetoid the size of mars bore down on the molten still forming earth as the two massive celestial bodies slow danced towards each other
02:24The planetoid approached at an oblique 45-degree angle and at roughly six miles per second
02:30So the collision would have been relatively speaking a low-velocity one
02:35however, the energy of the collision is
02:37enormous
02:39It really pulverized the planet
02:41And it splashed out a giant piece of the mantle of the earth just right off the planet
02:51Time and gravity caused that material to combine into earth's moon
02:57Generally accepted today this violent scenario for the moon's birth was first proposed in 1975 by dr. William hartman and dr. Donald davis
03:09But what evidence could possibly lead them to this exact reconstruction of such an ancient crash?
03:16They started by trying to understand what the moon is made of
03:20Studies of the moon in the 50s and 60s revealed the moon to be not nearly as dense as the earth
03:26The moon apparently lacks an iron core the way the earth has the earth has a fairly high density
03:32The earth is five grams per cubic centimeter rock is around three
03:38So we knew the earth was five so it's a mixture of this heavy metal and light rock
03:44But the moon was only about three so it looks like the moon is a rocky object
03:49But though the moon's density differs from the earth's it shares earth's chemical makeup
03:54In particular the variations of elements known as isotopes that were found on the moon were identical to those on earth
04:03Each part of the solar system has its own isotope composition you look at the moon
04:08It's right right exactly exactly the same oxygen isotope ratio, so
04:13That beautifully fit the idea that the moon material
04:18Really was part of the earth material originally
04:21So the moon has a similar composition he had a different density hartman and davis suggested that this similar yet different scenario
04:30Resulted from an impactor earth collision that gave birth to a moon composed partially of pieces of earth's mantle
04:37If you hit the earth with something big enough you could blow a lot of the crustal and
04:43Mantle rocky material off the outer part of the earth
04:46Here's the nice little iron core in the middle and here's the rocky part around it
04:50You know hit that you blow off all this rocky material big cloud of debris around the earth and the moon forms out of that cloud
04:57Then you get a moon that looks like what we've actually got today a
05:01Good theory, but what it needed was backup in the form of computer modeling
05:06When we're trying to describe how the moon formed we start with an idea in this case
05:11The idea is that the moon formed from a large collision with the earlier then we build
05:16Models in this case computer simulations that actually describe what happens during such collisions a model with earth's current rotation
05:25And the moon size as constraining factors
05:28We have to produce an earth spin from this impact that gives us this 24-hour day
05:34Feed the data into the model and you peer back in time to a much different earth
05:40Rotating once every four hours in the opposite direction before it's hit with a glancing blow by a slow-moving impactor roughly the size of Mars
05:49When the impactor struck its angle size and speed all conspired to reset the earth spin
05:56The fact that it was a slow speed collision was a lucky break for the earth if the impacting object is coming at too high a speed
06:04You can actually blow a planet apart in this case the earth and the impactor blew apart and the impactors iron core
06:12Fell back toward earth the iron core of the impactor would have merged with the iron core of the earth
06:18So that it would have increased the earth's core mass somewhat
06:21This reassembly process left behind a fairly hellish earth
06:27The earth's temperature would have risen to
06:3010,000 to maybe 20,000 degrees in the interior
06:34The impact filled the planet's atmosphere with thick silicate particles of vaporized rock
06:41After something like a thousand years that silicate atmosphere of the earth begins to cool and condense
06:47Despite its cataclysmic beginnings the moon earth relationship is all about stability
06:52The moon's orbit and gravitational pull are responsible for maintaining the earth's tilt within about one degree
07:00Without the moon our models predict that that tilt would actually vary
07:06From angles as small as zero degrees all the way over to about 60 degrees
07:10So you'd have the north pole almost facing the Sun head-on at times
07:15Those non-impact conditions wouldn't have ruled out life, but it certainly would have made conditions far more challenging
07:25So while spectacularly destructive the impact that formed the moon was a lifesaver for earth
07:33Collisions in our solar system both destroy and shape worlds
07:37Why do we want to understand impacts this?
07:41turns out
07:43To have a lot to do with who we are and what our solar system is like. I think it really is an important cosmic question
07:53Evidence brought back from the Apollo moon landings also helped resolve another moon controversy
08:01Just what exactly caused the moon's Swiss cheese complexion?
08:05Was the popped moon scape a relic of a volcanic past or could it be further evidence of violent impacts within our solar system?
08:14Since the mid-1970s scientists have suggested that the moon itself is the by-product of a cosmic collision with earth
08:30But could its familiar surface be further evidence that objects in our solar system?
08:36Can crash into each other?
08:38Until the 1960s most scientists believed the craters covering the moon's surface were the dead cones of ancient volcanoes
08:45I came into graduate school in 1961 there's still books being published by
08:51reasonable reputable scientists
08:54Arguing in favor that all of the craters that we see on the moon are volcanic
08:58Gene shoemaker was one of the planetary geologists who had become convinced that the moon had been victim of millions of meteorite impacts
09:08His theory had grown out of his study of earth's impact craters which are difficult to recognize and rare
09:16But why are there so many craters on the moon and so few on earth on the earth?
09:22They often get wiped out due to atmosphere plate tectonics the things going on here on earth
09:32Shoemaker's work established that impact craters have distinct features
09:36These features can be replicated by firing a bullet into sand first of all there's a rim kind of a bowl-shaped rim
09:43Also, there's this thing called the ejecta blanket
09:46And this is when the meteor hits it sends out a whole plume of debris and that forms a blanket around the crater
09:55Shoemaker catalogued the anatomy of impact craters by studying the craters left over from atomic bomb tests at nevada's yucca flats
10:03As a result of his work earth's impact craters seem to come out of hiding
10:13Armed with his understanding of earth's craters shoemaker intended to use the apollo moon landings to prove that the moon is covered in impact craters
10:22He trained the apollo astronauts to take samples that would test his theory
10:26Make them take the rock hammers out and walk around and actually understand the geology of the earth so that when they went to the moon
10:34They'd be able to think a little bit like geologists
10:38Armed with shoemakers training the apollo astronauts provided the evidence that scientists like shoemaker needed to prove that the craters on the moon
10:46Were impact craters not extinct volcanoes the moon is a witness
10:51The apollo era astronauts brought back moon rocks and all these basins seem to be nearly the same age that is telling us something
11:02Rock samples from the craters that covered the moon taken during nasa missions during the 1960s and 1970s
11:09Dated most lunar craters to a specific period a long time ago
11:13The nasa samples dated the impacts to roughly 3.8 to 4.1 billion years ago
11:23Some scientists believe there must have been another swarm of impacts after the solar system formed this period of intense
11:30Asteroid impacts on the inner solar system has been dubbed the late heavy bombardment period the planets got the stuffing knocked out of them
11:37The earth and the moon and all of the planets were just pummeled with material from space
11:45according to some scientists the heavens produced an onslaught of asteroids and meteoroids during this period
11:51for roughly 300 million years
11:54Massive bodies wafted through the solar system orbiting the sun and intersecting the orbits of the inner planets
12:00There was a lot of cosmic bullets that were flying around they were just flying everywhere
12:07But what caused the bombardment?
12:09There's a spike in impacts that might have been actually triggered by motions of the outer planets on the outer solar system
12:15Sending in a barrage of comets and asteroids into the inner solar system
12:20Some scientists speculate that there may have been a domino effect that started when jupiter and saturn's orbits shifted causing a tug of war between the planets
12:30This gravitational disturbance upset the orbits of a ring of debris called the asteroid belt found between the inner and outer solar system
12:40This debris then began to intersect the orbits of mercury venus earth and mars plus their moons
12:48This event happened almost a billion years after the solar system formed so it sort of occurred during the late teenage years
12:56And the planets and the moon were sweeping up all the debris that was left over from the formation of the solar system
13:03Fortunately for us cosmic collisions at a rate matching the late heavy bombardment period are gone for good in our solar system
13:13Every time one of these things runs into a planet you have one less that's whizzing around the solar system
13:18So you can think about you know the planets kind of going around and sweeping these things up over billions and billions of years
13:23And there's going to be fewer and fewer of these objects around
13:25Fortunately for us
13:26We've gotten to a place in the solar system history where there's relatively few of these things
13:31And so we can expect to go for a fairly long period of time without getting smacked by one of them
13:36But we cannot stop watching the skies because every so often one planet or another in our solar system does get smacked by a severe impact
13:48In 1994 a massive snowball made a beeline for a giant ball of gas and turned the earth into a stunned eyewitness
13:57Rock samples from the Apollo missions to the moon convinced most scientists of the severity of what is known as the late heavy
14:07Bombardment period when our solar system was trashed four billion years ago
14:13But even into the 1990s
14:15Many still believe the likelihood of a modern impact with a large object was virtually nil
14:20But geologist gene shoemaker set out to show that massive collisions in our solar system were not entirely a thing of the past
14:29There were a lot of jokes about chicken little it really
14:33Was out there as an idea on the subject of science fiction movies
14:38But to take it seriously it was a little difficult to do because you've not heard of anyone who died being hit by an asteroid
14:50But shoemaker was one of those who took the possibility of an earth-killing asteroid impact
14:55Seriously, he hoped the public would recognize the need to search for future unwelcomed guests of earth
15:02He would need more, but some believed otherwise
15:07Miraculously in 1993 the heavens gave him all the proof he'd ever need
15:12On the night of march 24th 1993
15:18gene shoemaker his wife carolyn and amateur astronomer david levy were observing on the schmidt telescope at the palomar observatory in san diego california
15:29But it was a cloudy night not the best for peering into deep space
15:34They were about to give up and i'm looking at the sky
15:37And i'm noticing there's some holes in the clouds and i'm thinking you know
15:42There are some breaks in the clouds maybe we should continue to observe in the hope we might get something
15:49david was always very enthusiastic and he would really push the limits as far as the film was concerned
15:56But gene shoemaker was reluctant film was expensive and the night wasn't promising david levy wouldn't give up
16:03Levy won out they took just two pairs of films that night
16:08Reviewing them two days later carolyn shoemaker knew she had something unusual
16:13She suddenly sat up in her chair and she said david gene
16:18i don't know what i have here but it looks like a squashed comet
16:24None of us knew exactly what we had because it wasn't like anything we had seen before
16:29Seeking confirmation of their find levy immediately called his friend james scotty who was observing at kitt peak near tucson arizona
16:41scotty was doubtful of their findings but agreed to take a look
16:46i called him back in a couple of hours i said are you okay and he said the sound you heard is me
16:52trying to pick my jaw off the floor and i said jim do we have a comet he said oh yeah you've got a comet
17:00a comet is an icy body sometimes containing a rocky core that orbits the sun
17:07we typically now use asteroid as being something that's rocky
17:10and a comet is being something that's icy the problem with that definition is i think we're beginning to realize
17:16that many objects in the asteroid belt are actually icing and depending on where they were born
17:23they either have a lot of water ice because they were far from the sun or they were formed close
17:28to the sun in which case they're pretty much water free comets can be hard to predict because their
17:35orbits can be of extremely long duration up to a million years to revolve around the sun
17:40orbital calculations of shoemaker levy 9 as the comet had been dubbed revealed that it had passed
17:47close to jupiter in july of 1992 and that jupiter's gravitational forces had broken it into 21 fragments
17:56comets can be pretty fragile and so you would see one fragment here and another fragment there but you
18:03never saw them lined up like this and so it was a very exciting discovery it was really
18:10a string of pearls very dangerous pearls that calculations revealed to be on a collision course
18:17with jupiter this was fantastic news to gene who had always wanted to see an impact but reactions in
18:27the scientific community were decidedly mixed i remember the day that it was announced that shoemaker
18:35levy 9 was in fact going to hit jupiter because a graduate student came into my office and said if
18:41you heard if you heard a comet's going to hit jupiter and i said jupiter is really big comets are really
18:47small it's not going to be a big deal and this was the question what kind of an impact would a big snowball
18:54hitting a gaseous giant of a planet make gene shoemaker believed that the incredible speed of the shoemaker
19:01levy object would create a spectacular collision with jupiter but again few believed him we didn't
19:08know that much about the makeup of comments how strong they were we just hoped for a big show nobody
19:16thought that the results were going to be as dramatic as they were shoemaker was right the world watched
19:23from july 16th through the 22nd 1994 as one after another the fragments of comet shoemaker levy 9
19:31made a spectacular collision into jupiter's clouds
19:37and these pieces kind of came in in a line like a like a train like a freight train and just hit the
19:41planet you know bam bam bam bam plumes rose 2 000 miles above jupiter's cloud tops the fact that you
19:50could have fit the earth within the dark cloud coming from one fragment strike that was pretty
19:59awesome awesome might just be an understatement a two mile long fragment in particular labeled fragment g
20:07struck with an energy of six quadrillion tons of tnt 600 times the power of the world's entire nuclear
20:15and conventional arsenal this is something that really happens once in a lifetime our understanding
20:23of the solar system is evolving by leaps and by bounds as we watch that's the way to do science
20:33it proved beyond any doubt that impacts were not only possible but inevitable and very dangerous
20:39some speculate that if a piece of a comet the size of fragment g struck earth it could extinguish most
20:47life on the planet an awareness of the continued danger of collisions in our solar system is just a
20:55part of gene shoemaker's legacy in 1997 he died in a car accident while studying impact craters in alice
21:03springs australia i remember i was at a dinner where somebody asked someone that i know well who is the
21:09greatest planetary scientist who is the greatest geologist of the 20th century and he didn't even
21:15think he said gene shoemaker without a doubt gene shoemaker helped the world understand that impacts
21:23within our solar system are still disasters waiting to happen but have massive impacts also helped form our
21:30planetary neighbors change their makeup and even their posture for instance why does mars have two faces
21:41and why is uranus resting on its side
21:53a chunk of solar system debris one-tenth the size of earth's moon hurdles through space
21:59rocks and debris cross its path and get obliterated leaving pockmarks on its surface it's on a collision
22:07course with mars
22:11the impactor and mars are about to test the ability of two objects to occupy the same space at the same
22:18time the planetoid slams into mars in a cataclysmic collision scattering dust and debris
22:25it's just another rough day in the life of the inner solar system four billion years ago this was the
22:33largest impact our solar system has ever endured yet the evidence was all but hidden until just recently
22:40the mystery began in june of 1976 when the viking one orbiter cruised through space at the tail end of a
22:4910-month journey to mars as it began its orbit around the red planet it started sending images back to earth
22:58the orbiter and its companion viking 2 completed more than 2 100 trips around the planet and sent back
23:05photos of mars canyons craters volcanoes and lava plains the photos also revealed a curious division in the planet's surface
23:15mars has what we call a hemispheric dichotomy where the northern half of the planet is sitting at a low
23:22elevation and has a very smooth surface but the southern half of the planet has a high elevation and
23:26and as much rougher surface and we've known about this dichotomy actually for about 30 years now
23:32the big mystery has always been how it formed in the 1980s astronomer stephen squires and geologist
23:39don wilhelms proposed a radical theory to explain the dichotomy in the martian surface the so-called
23:46giant impact theory rests on the idea that the northern lowlands of mars may actually be the largest
23:52impact crater in the solar system as big as asia europe and australia combined covering roughly 40
24:01percent of the martian planet but there were problems with this theory scientists studying
24:07the outline of the crater saw what appeared to be more of a kidney bean shape and not the ellipse that
24:13would have been expected from this type of impact recently a team of scientists including jeffrey andrews
24:20hannah and bruce bannert set out to create a clearer picture of the impact crater using topographical and
24:27gravity measurements they were able to look below lava flows in mars tharsis region which contained
24:33some of the largest volcanoes in the solar system once they subtracted the effects of volcanic activity
24:40they could see the crater's actual shape so we were able to look at what was there perhaps four
24:46billion years ago and when we did this we found that the boundary instead of being this very irregular
24:51kind of kidney bean shaped thing turned out to be this very regular ellipse this was a very important
24:57observation because there's really only one process that we know of that's capable of producing an
25:03enormous elliptical depression like this and that's a giant impact the largest impact basins in the solar
25:08system are all actually elliptical in shape simulations indicate that the impactor would have to have been
25:14around 1200 miles in diameter or roughly the size of pluto hurtling through space at 20 000 miles per
25:22hour and striking mars at a 45 degree angle so it's an enormously energetic impact not surprisingly the
25:30mars impact is estimated to have occurred during the late stages of our solar system's formation four
25:36billion years ago and it is one of two massive planetary impacts that still scar our solar system
25:44evidence of the other impact can be seen in the off-kilter attitude of uranus as solar system
25:52planets go uranus is fairly dull it has rings but they are not nearly as spectacular as saturn's
25:59an ice giant uranus is puny compared to its gas giant neighbors jupiter and saturn like earth uranus
26:06has a solid core but this is where its similarity to earth ends we couldn't land a spaceship on it it's
26:13got a thick thick atmosphere so heavy that it was almost like a pudding and that pudding sits on a
26:20bed of ice that makes up the ice giant's mantle but the one spectacular feature that sets uranus apart
26:27from the other planets uranus is extremely askew for years this strange alignment of uranus baffled
26:35astronomers but one leading theory first suggested by soviet astronomer victor safranoff in the 1960s
26:43suggested that the cause was a massive impact from an object perhaps as big as earth
26:50all planets have a rotation axis so here's the planet here's the north pole south pole
26:54and we're leaning at 23 and a half degrees mars is leaning at 25 degrees jupiter's about zero degrees
27:01but uranus is very strange because it's actually tipped a little bit past 90 degrees
27:06and safranoff pointed out that that you could do that by hitting uranus with something that as i
27:12remember was three percent the mass of uranus itself so imagine a planet rotating like this
27:19it's a round planet gets maybe hit tangentially right at the top that tips it over you know the
27:25debris gets thrown off and you've now rotated this planet off to the side
27:33not only do impacts knock planets on their side like uranus
27:37and give the surface of planets complete makeovers like what happened to mars but objects can hit
27:43planets so hard pieces break off only to fall into other planets we know meteorites can land in fields
27:52deserts and just about anywhere else but every so often these meteorites are actually dislodged
27:58chunks of other planets bringing us information from another world
28:05our solar system isn't a tidy place chunks of debris that never coalesced into planets
28:11float around in the asteroid belt between mars and jupiter like so much unfinished business spoiling
28:18for a fight collisions beget collisions as impacts dislodged chunks of planets that themselves
28:25eventually crash into planets these pieces are tangible evidence of impacts within our own solar system
28:32impacts that happened billions of years ago millions of miles away and this chain reaction occasionally ends
28:38with these visitors from a distant place landing on earth bringing us information about the solar system
28:45they'll fly through the atmosphere at a tremendous speed and generate heat pressure start to burn
28:52and many times these fragments will explode in the atmosphere and then rain down on the planet in showers
28:59every child who has looked at the sky and seen a shooting star has seen an impact of extraterrestrial
29:08origin many of us have seen cosmic collisions we just didn't realize that's what they were
29:14meteors burning up in our atmosphere are common but infrequently some part of the meteor will survive to
29:21impact the earth by virtue of its survival it has earned the right to a new name meteorite and it now
29:27has a bounty on its head
29:31a rare breed of people meteorite hunters make it their business to track down these precious rocks
29:37that have traveled through our solar system in a pursuit that is part science part commerce and part hobby turned obsession
29:45jeff notkin and steve arnold are two of the world's most prolific and determined meteorite hunters
29:51sometimes we travel to godforsaken corners of the world that nobody would want to go to in their
29:55right mind all in the hope of finding little pieces of cosmic debris why do we do it meteorites are amazing
30:04they're a chance to hold a bit of an alien world in your hand they're also treasure these pieces of
30:13other planets that land on earth there's a hierarchy of meteorite value not surprisingly the rarest rocks
30:20have the most value pieces of the planet mars were blasted off into space by other meteorite impacts on
30:28the surface of mars of the many many thousands of different meteorites that have been found on our
30:34planet only about 30 are from mars so they're among the rarest extraterrestrial material that we've ever
30:42recovered martian meteorites are 35 times more valuable than gold by weight this little piece
30:49here it's about 15 grams and it's a piece of mars a conservative valuation on this piece would be about
30:57fifteen thousand dollars so everything else on this table put together would not even equal the value
31:03of this one specimen as is true with many other meteorites they can tell us information about
31:10the makeup of one of our neighboring planets logistics and cost have prevented us from going
31:18to mars and bringing back a sample but the universe has delivered these rare examples to us free of
31:24charge through ancient impacts meteorites can also go beyond informing us about other planets
31:33they have often served as a springboard for technological advances in the space program meteorites were studied
31:42in the early days of spacecraft design this is a very efficient shape for traveling through the atmosphere
31:49as this meteorite flew through the atmosphere towards earth it kept this face oriented towards our planet hence the
31:59origin of the term orientation so as it flew towards the earth in that fixed position the surface melted and
32:07it curved back to form this beautiful shield shape behind the shield the meteor melts and warps approaching
32:15temperatures greater than 1000 degrees celsius and this demonstrates very clearly the thumb printing that's so
32:23unique to meteorites these little indentations that are created as the surface melts so meteorites that show
32:31orientation are not only rare but they're very appealing to collectors who are interested in
32:38the sculptural aspects of meteorites and what happens to them when they fly through the atmosphere
32:43you could never find the terrestrial rock a rock from earth that looked like this it's specifically
32:50it's fiery journey through the atmosphere and the melting that has created this which you might
32:56describe as an outer space sculpture but despite all their physical appeal these space sculptures don't
33:03hold the value of their martian cousins or even their lunar counterparts pieces of the moon are second in
33:11rarity and value lunar impact craters are launching points for debris some of those craters are enormous
33:18those ancient impacts will have thrown a huge amount of lunar material into space and every now and then a
33:26little piece of it makes it here but most meteorites are refugees from the asteroid belt we can't physically
33:34get out to the asteroid belt yet as people so meteorites allow us the chance to study the makeup of other
33:45worlds in our solar system there are sites that continue to be rich in meteorite finds
33:53brenham kansas has become famous for all sorts of digging this site here is the brenham strewn field
34:02somewhere between two and ten thousand years ago a giant meteor exploded coming in from the west northwest
34:09broke into a bunch of pieces and scattered pieces out in this farm ground out here meteorites have
34:16definitely been found in this very field that we're in it's exciting to be in a field you know that they
34:21were here are there any left that's what we're here to figure out to date four tons of meteorites pieces of
34:29our solar system have been pulled from these fields including steve arnold's find of a 1430 pound world
34:37record sized palisite meteorite these meteorites are composed of stone and iron and contain crystals of
34:44the mineral olivine palisites are rare valuable and it takes work to find them like farmers working a field
34:53jeff and steve must cover every foot of ground miss a spot and they may miss the meteorite
35:04okay
35:10this is where we go pinpoint it see what it is
35:15digging is never easy but there's an adrenaline rush that comes with the hunt
35:20the possibility that they're standing on top of a meteorite worth tens of thousands of dollars
35:25makes the hunters dig a little less back breaking but no less disappointing when they find a so-called
35:31meteor wrong like this rusted wheel it's actually one of the cooler meteor rungs that we found no kidding
35:39but it's also worthless
35:42their meteorite hunt continues in a field two miles to the south
35:50oh wow meteorite hunting sounds like such an exciting and exotic lifestyle but this time
36:01the excitement is actually warranted they've hit something with a shape and metal content suggesting
36:07that it's a meteorite
36:12could be a fairly nice size actually
36:15i got it
36:15oh look at that congratulations congratulations buddy
36:23this guy's been buried down there for we don't know five ten fifteen thousand years
36:29just waiting for today you brought out into the light the meteorite's classic shape
36:35its face flattened by the heat of entry into earth's atmosphere
36:38and its weight around 40 pounds could make it a premium fine
36:44twenty twenty five thousand dollars maybe
36:50when a meteorite arrives here not only has it survived this incredible burning passage through
36:59our atmosphere but it's a bit of the history of a long vanished world that we'll never see that we'll never get to
37:07so we learn about the cosmos around us by studying meteorites
37:16meteorites from other planets can survive the journey through the solar system to bring
37:20us a tantalizing glimpse of other worlds could evidence be hiding within these alien rocks evidence of extraterrestrial life
37:35life we search our solar system for extraterrestrial signs of it
37:44we relentlessly investigate its origins here on earth but where did life really come from
37:50not just the first organisms but the building blocks from which all life evolved
37:55it turns out that cosmic collisions may be key to spreading the seeds of life throughout our solar
38:02system and the universe life on earth formed roughly 3.5 to 3.8 billion years ago
38:10just as the chaos of our solar system's late heavy bombardment period began to die down
38:16and conditions allowed for the formation of water
38:19amazingly the asteroids and comets that crashed through the solar system during this period may
38:26have had a lot to say about when and where life formed that's because the organic molecules that are
38:32the building blocks of life here on earth can be found wafting through space in the cores of comets
38:39and on the surface of asteroids we are made up of much the same stuff that our environment is
38:46in fact even more so we're made up of stuff that comes from heavy stars as they explode and become
38:53supernova and their material is spread all about through space some of it hits us in the form of
38:59comets and then that becomes us so in a way we are star stuff we are made out of comets literally for
39:08example the iron in our bloodstreams was formed during the death of stars millions of years ago in the
39:14latter stages of a star's life after its fusion process has consumed its hydrogen and helium it
39:20produces iron that iron is distributed through space when the star dies and explodes this distribution
39:29system scattered life's building blocks throughout our galaxy and beyond so when we look up at the
39:34night sky it's hard not to wonder if there's life out there surprisingly collisions in our solar system
39:42can bring the search for extraterrestrial life right down to the surface of earth
39:47in 1984 in antarctica meteorite hunters found a strange rock that kicked off a storm of controversy
39:55about the possibility of life on mars
40:01the meteorite itself was just a chunk of rock on the surface of mars
40:05uh happily minding its own business when another large meteor hit the planet mars and put enough
40:12impetus behind the rock to release it from the martian gravity and sending it out into the solar system
40:17where it wandered around for a while before encountering the earth's gravity well and fell onto the earth
40:22the rock was dubbed alh 84001 and it may be the most important rock ever found today rock 84001
40:34speaks of the possibility of life the simplest explanation to us is martian life it actually had
40:43traces of carbon compounds in it under the microscope they saw some some structures that were very reminiscent of
40:51simple life forms and so the inference was that these rocks actually contained evidence of life on mars
40:59alh 84001 seemed to contain microscopic fossils of ancient martian bacteria
41:07there were four lines of evidence the presence of the mineralogy itself
41:11the presence of small grains of iron minerals called magnetite which are present in earth bacteria
41:18the presence of the fossils and the presence of carbon-based material that on earth is indicative of certain life
41:27processes taken all together those four lines of evidence were used to come up the hypothesis that there was
41:33ancient life on mars these findings sparked both hope and fierce debate could some ancient collision in
41:40our solar system really have dropped the first evidence of extraterrestrial life right in our backyard
41:47that was a very controversial conclusion and it's not considered to be correct by the majority of scientists
41:55that looked at it but that certainly raised the interest level by about a thousand times over what a regular
42:01rock would have done scientists have suggested that the rocks organic molecules are the result of
42:07contamination from the antarctic ice or that they may have been created by non-biological processes
42:15despite the setback the search for extraterrestrial life continues
42:19places where life can happen it will happen we see life in very remote environments very extreme
42:27environments on the earth life seems to be a resilient property of the universe
42:36and comets and asteroids are virtually a shopping bag of ingredients for making life suggesting that the solar
42:43system is rich with life making potential could life have been seeded throughout the solar system by
42:50these objects could planetary impacts have thrown ingredients for life into space where they could
42:56seed some other planet why not we know impacts occur all the time and these impacts are both a blessing and a curse
43:06could that kind of impact be the ultimate limiting factor maybe planets where evolution is going
43:12along great and you have intelligent civilizations and they're about to build starships and go flying
43:17off to the rest of the universe and then kablooey an asteroid comes in at the wrong time you know we
43:22don't know what really the evolution of systems is collisions built the planets and they continue to bring us
43:29information from the solar system and every so often they pack a life-threatening punch