Dark history of earth? पृथ्वी का संपूर्ण इतिहास ? full Documentary
Dark history of earth? पृथ्वी का संपूर्ण इतिहास ? full Documentary
S06E03
Our solar system hides a dark and violent past, and new discoveries reveal that Earth and the planets were formed from the destruction of alien worlds that came before us.
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Content
1.26 -> The Earth is over
4.5 billion years old.
6.28 -> Its history is shaped by disaster...
12.02 -> after disaster.
14.36 -> Asteroid and comet collisions,
flares from the Sun.
18.36 -> Mass extinctions, supernova
explosions, cosmic ray bombardment.
24.12 -> You name it, we've experienced it.
26.34 -> It's kind of a miracle
we're here at all.
30.24 -> These violent events could be why
Earth has life.
35.22 -> We tend to think of disaster
as a bad thing,
38.2 -> but out of chaos
can come possibility.
41.24 -> When we destroy something,
we can also create something new.
47.08 -> Earth has walked the line
between survival...
51.02 -> and destruction.
52.42 -> It's tipping that fine balance
of luck,
55.22 -> between a good disaster
and a bad disaster.
58 -> Could catastrophe and chaos be
the essential ingredients for life?
81.18 -> 2021, scientists investigate
something mysterious
86.04 -> buried deep inside the Earth,
89 -> it's a long, hidden clue
to our violent past.
94.34 -> Deep down 1800 miles
below the surface of the Earth,
98.08 -> our core is surrounded
by fluid rock,
100.4 -> but, inside that, 600 miles high
and thousands of miles across,
106 -> are two denser regions,
107.28 -> and they kind of cup the core
of our planet like two hands.
112.18 -> One of them is, you know,
half the size of Australia
114.16 -> for crying out loud.
115.06 -> So, I mean, they're big
lumps down there.
117.18 -> There's no reason they should be
there, it's a mystery to us.
123.04 -> To solve this mystery,
scientists need to examine the rocks
127.02 -> buried over 1,000 miles
beneath the surface.
132.1 -> We don't really know what these
two big rocks are made of,
135.04 -> sitting there on the core.
136.28 -> However, we've been able to
sample them.
138.28 -> How in the world is that possible?
141.16 -> Well, these blobs are actually
feeding mantle plumes
144.1 -> that are rising up
through the mantle.
147.2 -> So, volcanoes in Iceland and Samoa,
for instance,
150.04 -> will dredge up some of these
lumps of rock from the mantle,
153.32 -> it's a precious chance for us
to sample some of that deep rock
156.46 -> that we'd normally
not get a chance to see.
161.44 -> These rocks are old.
163.28 -> Very old.
165.44 -> It turns out that the samples
in the lava,
167.36 -> that we think came from these
blobs of rock in the mantle,
170.14 -> are 4.5 billion years old.
173.3 -> That is as old
as the age of the Earth.
177.12 -> So, they tell us something about,
179.04 -> you know, how the internal structure
of our planet
181.36 -> was arranged in the earliest days
of the formation of our planet,
185.2 -> so, getting samples from that time
is very, very important.
188.4 -> The age of the rocks
may be a clue to their origin.
192.48 -> They date back to a time
of monstrous, cosmic mayhem.
202.16 -> Four and a half billion years ago
203.34 -> the solar system
was still a pretty wild place.
207.3 -> We're approaching the end of
the formation of planets.
210.24 -> Earth would still be growing.
214.46 -> Back then, you wouldn't necessarily
recognize the Earth.
219.08 -> In fact, you wouldn't recognize
the Earth at all.
221.12 -> For example, no moon,
222.4 -> the Earth did not have a moon
when it first formed.
226.36 -> The young Earth orbits the Sun
with other infant planets.
232.3 -> One of them is an object
scientists call Theia.
237.46 -> And it's on a collision course
with our home.
247.34 -> The Theia collision would have been
a spectacular event,
250.16 -> it would have been
one of the coolest things
251.38 -> you could possibly witness,
and the origin of the solar system,
254.16 -> certainly the biggest event
in the history of the Earth.
261.2 -> The Theia event is something that
completely reshaped the Earth.
266.24 -> The planet that the Earth was
before the Theia event is gone.
271.02 -> Forever.
272.32 -> The impact melts rock
274.28 -> and throws out over
a billion, billion tons of debris.
280.1 -> During this incredible collision,
282.24 -> these two planets were
literally broken apart
284.44 -> and combined into one big planet.
287.26 -> Huge chunks of Theia stayed together
290.02 -> as the now molten Earth
began to form anew.
294.12 -> Now, we can kind of paint a picture
of where these big lumps of rock
297.02 -> might have come from,
they're very old,
299.12 -> they're in fact the same age
as that large impact event.
303.48 -> They could be pieces of Theia.
307.28 -> The giant slabs of Theia
sink down into our planet.
313.2 -> And lie undiscovered
for billions of years.
322.1 -> Earth reforms
from the ruins of both planets.
327.26 -> Now, you might think that
a collision like this
330.12 -> is just devastating,
there's no upside at all.
332.34 -> But there are some things
that came out of this collision
334.38 -> that may have led
to the possibility of life.
339.32 -> When these two planets combined,
341.32 -> parts of Theia's iron core
merged with Earth's.
347.06 -> So, that means that Earth collected
a much bigger core
349.22 -> than it might have possessed
on its own.
351.26 -> This is good news for us,
352.3 -> because the core is the source of
the magnetic field that protects us.
356.44 -> Liquid metal flowing around
in the outer core
360.02 -> generates Earth's magnetic field.
363.44 -> A protective shield from the Sun.
369 -> The Sun can actually output
billions of tons
371.34 -> of high energy protons
and electrons in a single burp.
376.18 -> That eventually would have
stripped away our atmosphere.
378.46 -> If it weren't for that active core
and that magnetic field
381.44 -> we would look like Mars, just
sort of a bare and barren desert.
386.12 -> Thanks to Theia's extra iron,
Earth's molten outer core is large.
392.32 -> So, it cools slowly, staying molten,
396.12 -> and keeps on generating
a strong, magnetic shield.
402.08 -> Because of that collision,
the extra iron, the extra heat,
405.42 -> we've stayed active, we have
a magnetic field, we are protected,
410.12 -> and, in fact, that's why
we're here talking about it.
414.18 -> The catastrophic impact
helped life in other ways.
418.34 -> The Theia event was absolutely huge,
420.42 -> not an impact like 100-mile asteroid
making a big crater in the desert,
425.18 -> but a planet hitting a planet,
causing a huge disc of debris
430.4 -> spread out from the Earth,
out of which formed the moon.
439.12 -> After the collision,
440.28 -> the Earth tilts on its side
and spins incredibly fast.
447.08 -> A day only lasts a few hours.
452.26 -> The Earth itself rotates
slightly on its side,
456.1 -> and if left to its own devices
459.06 -> would in fact experience
unpredictable,
462.34 -> chaotic wobbling.
464.3 -> The fact that the moon is there
stabilizes the Earth,
468.2 -> stabilizes our climate.
472.22 -> The moon's gravitational pull
on our oceans creates tides,
477.02 -> and slows down the Earth's spin.
480.32 -> Creating a world primed for life.
484.1 -> We actually owe quite a bit to
the moon and Theia, its progenitor,
489.3 -> for making Earth
a hospitable planet for life.
494.1 -> A giant collision
four and a half billion years ago
496.4 -> sounds like a catastrophe,
499.02 -> but it was probably the best thing
to happen to the Earth.
503.24 -> Theia, I would shake your hand,
because we have a lot to owe you.
509.08 -> We also owe the science of chance,
512.36 -> because we lucked out
with a one in a million impact.
517.08 -> If the impact from Theia
had been harder,
519.38 -> the Earth may not have recovered
as well as it did,
522.2 -> and we may not be here
to talk about it right now.
525.14 -> If it had been a little bit
less forceful
527.38 -> then the impact of it may not have
made the changes that we think
531.18 -> were needed
for us to be here now.
533.38 -> We got lucky, most planets don't get
to survive a collision like that,
538.26 -> and get a bonus moon
out of the deal.
544.12 -> Earth's huge collision with Theia
546.4 -> was not our planet's first brush
with danger.
551.24 -> An earlier explosive event
could have stopped the solar system
555.22 -> from sparking into life.
558.26 -> And the Earth from forming.
564.16 -> Supernovas are one of the
universe's most destructive events.
570.22 -> Releasing, in one second,
573.34 -> as much energy as our Sun will
in its entire lifetime.
579.44 -> But rather than wipe us out,
582.2 -> supernovas may have kickstarted
the solar system.
586.28 -> 4.6 billion years ago,
587.34 -> the solar system was not even
really the solar system,
590.02 -> it's the precursor
of the solar system.
594.24 -> So, what we had was a cloud of gas
and dust collapsing in on itself,
598.44 -> forming the Sun in the center,
a big, flat disc around it,
602.26 -> out of which all the planets
were forming.
606.02 -> There were all kinds of vast clouds
of dust and gas
609.02 -> floating around the galaxy.
610.34 -> What actually causes them to start
collapsing and forming new stars?
614.38 -> Well, you have to give that cloud
a push.
617.32 -> Scientists think this push
could be a stellar blast.
624.4 -> A supernova.
627.44 -> Supernova are some of the most
powerful events in the universe.
634.04 -> One explosion can light up
brighter than a galaxy.
640 -> So, not only do the eject elements
and material,
643.1 -> they also eject a lot of light
and energy.
646.12 -> A supernova explosion
sends a shock wave
649.28 -> racing out into space
at 18,000 miles per second.
657.24 -> The shock wave
from a nearby supernova
659.32 -> compresses material together
661.22 -> until it begins to collapse
under its own gravity.
667.06 -> Was this
how our solar system started?
671.3 -> So far, it's been really difficult
to find evidence
674.38 -> that there was some supernova
or point to something that happened
677.2 -> that really kickstarted
the solar system.
680.14 -> The ancient supernova blast
faded away a long time ago.
687.54 -> Imagine a crime scene,
689.58 -> now imagine waiting 4.6 billion
years after the crime is committed
693.98 -> and looking at it and going, there's
nothing here, what are we doing?
697.94 -> That's kind of
what we're trying to do here.
701.62 -> Researchers from
the University of Minnesota
704.02 -> tried to solve this ancient crime,
707.58 -> by studying asteroids
that fell to Earth as meteorites.
712.64 -> Asteroids are critical
for understanding
714.78 -> the early solar system,
716.56 -> and this is because they have
frozen in place all the conditions
719.64 -> that existed
in that very early solar nebula,
722.66 -> right at 4.5 billion years ago.
726.02 -> The asteroids contain information
about the time
729.7 -> leading up to the birth of the Sun
and the solar system.
735.56 -> When a massive star ends its life
as a supernova,
737.54 -> it undergoes what we call
nucleogenesis,
739.86 -> in fact, we call it
explosive nucleogenesis.
742.8 -> Literally, the explosion is
generating new types of nuclei,
746.78 -> new elements, heavier elements.
750.54 -> Well, it turns out,
the types of elements it makes
752.82 -> depends on the star that blew up.
758.76 -> The Minnesota team ran computer
simulations to investigate
762.94 -> which elements form
764.86 -> when a star, up to 12 times
the mass of the Sun, explodes.
771.8 -> Then, they compared the results
774.58 -> with analysis of elements
found in asteroids
777.82 -> dating back to the birth
of the solar system.
781.74 -> They match.
785.66 -> So, the remains of the supernova
787.66 -> was actually under our noses
all along
790.62 -> in the elements that have been
in our solar system for ages.
794.98 -> And, perhaps, in the Earth as well.
799.68 -> The Earth has lots of rocks
that's made of silicon,
802.02 -> that's only produced
in supernova explosions,
805.64 -> and the very core of our Earth,
the thing that keeps us alive,
808.6 -> that's iron, nickel, again, you only
get that in supernova explosions.
814.54 -> In February 2021, scientists shed
light on the supernova explosions
819.82 -> that helped seed our solar system,
821.9 -> and provide the materials
to build our planet.
827.72 -> The researchers examine fragments
829.84 -> blasted off the giant space rock,
Vesta.
834 -> 4.5 billion years ago,
and later landed on Earth.
842.74 -> These asteroid fragments contain
the fingerprints of not one,
846.68 -> but at least two
supernova explosions.
851.62 -> Our solar system was seeded,
was enriched,
854 -> by at least two separate
supernova explosions.
858.54 -> That's incredibly lucky,
859.88 -> because that is what delivers
the ingredients necessary for life.
865.88 -> Scientists believe
that these two supernovas
868.98 -> may have enriched different parts
of the infant solar system.
873.7 -> One provided the materials that
helped form the outer gas planets.
880.8 -> The other supernova
seeded the inner solar system
884.64 -> with elements
that built the rocky planets.
887.94 -> Including the Earth.
892.78 -> And the scientists think
they can even tell
895 -> the type of supernovas responsible,
897.74 -> one was a core collapse supernova,
900.78 -> a giant star that likely lived in
the same stellar nursery as the Sun.
908.58 -> It ran out of fuel and
collapsed in a huge explosion.
919.74 -> We think that this supernova
fed the outer solar system.
927.76 -> The other was what we call
a type 1A supernova.
932.98 -> It's caused by a small white dwarf
star cannibalizing another star.
940.6 -> What we think happens is that a
white dwarf has a companion star,
944.56 -> which is either another white dwarf,
or a bigger star, like a red giant.
948.54 -> And the white dwarf accretes matter
from the companion star.
952.68 -> If they accumulate too much mass
they can reach a critical density,
956.8 -> forcing them into a runaway
supernova event.
960.84 -> The type 1A supernova
explodes with extraordinary force.
966.62 -> Blasting material
across interstellar space.
971.72 -> Donating elements
to the heart of the gas cloud
974.58 -> where the inner rocky planets
will form.
979.74 -> Once again, our fate came down
to pure chance.
984.54 -> A series of extraordinarily
violent supernova blasts
988.56 -> gave the solar system
the kick-start it needed
990.94 -> and the elements
to build the planets,
993.74 -> without destroying our future home.
996.98 -> It's a fine line between being
too close to a supernova,
999.96 -> which will just shred
your pre-stellar cloud.
1003.02 -> And not too far away that you don't
get any of the good stuff.
1008.54 -> Supernova play both creation stories
and destruction stories,
1013.56 -> they play both roles.
1016.66 -> We lucked out.
1018.58 -> This chapter of the story ends well.
1021.64 -> The solar system
gets the ingredients it needs
1024.56 -> to build planets,
1026.58 -> Earth forms in a good location,
close to its star.
1031.84 -> The future looks bright.
1033.92 -> But then, the biggest bombardment
in history smashes into the Earth.
1046.08 -> From the moment our planet formed...
1049.34 -> we've been under fire.
1055.32 -> 2021, a fireball streaks across
the night sky in Europe.
1062.3 -> 2018, a 1500-ton meteor
explodes over the Bering Sea,
1068.14 -> with ten times the energy
of an atomic bomb.
1075.12 -> 2013, an asteroid explodes over
Russia, injuring over 1,000 people.
1083.36 -> The Earth is hit by
quite a few asteroids every day,
1086.26 -> you see them as shooting stars,
meteors in the sky.
1089.42 -> These events are violent
and destructive,
1093.08 -> but, these space invaders
also brought something
1096.54 -> every living planet needs.
Volatiles.
1101.08 -> When we say volatiles,
what we mean are elements
1103.26 -> that are really light and easily
moved around, often they're gases,
1106.44 -> so, that's oxygen
and water and carbon dioxide,
1110.26 -> and just all those light elements
1112.1 -> that are really important
building blocks for life.
1114.32 -> These elements are abundant
on our planet today.
1117.52 -> But, were not when it first formed.
1121.36 -> From observing other solar systems
forming all around us in space,
1125.24 -> we know the planets as close
to their stars as we are to the Sun,
1128.38 -> when they formed,
they were very hot and dry.
1130.5 -> There's probably some
little bit of water around there,
1132.56 -> but really not very much.
1136.14 -> So, what this means is,
1137.3 -> any volatiles will basically
be boiled away.
1140.42 -> You have a molten surface, anything
like water is gonna get boiled away.
1148.18 -> Young Earth was a dry planet,
1150.36 -> devoid of all the precious
volatiles needed for life.
1155.4 -> These materials must have been
delivered to Earth
1158.52 -> after its formation.
1164.32 -> We think volatiles arrived in the
early days of the solar system.
1169.4 -> When the giant planets,
including Jupiter moved around
1174.42 -> and stirred up the contents
of the solar system.
1179.34 -> As Jupiter moves, its gravity is
pulling on all the objects in there
1182.56 -> and basically speeding them up.
1185.1 -> There's a little bit of chaos there
in the first place,
1186.44 -> but now Jupiter is basically
supercharging it.
1190.3 -> Jupiter's path sends
countless asteroids and comets
1194.22 -> on a collision course
with the Earth.
1198.1 -> It would have been utterly chaotic,
1200.2 -> this is a rain of large objects
onto all of the inner planets,
1204.34 -> but these objects that came
screaming into Earth were gigantic.
1210.48 -> Four billion years ago, a storm
of giant asteroids and comets
1216.08 -> hits the Earth.
1218.12 -> Some are tens of miles wide.
1221.3 -> They bring the volatiles
that help fill the Earth's oceans
1225.08 -> and build its atmosphere.
1228.12 -> But cosmic deliveries
can both give and take.
1233.36 -> The importance of impacts
for atmosphere could go either way,
1237.1 -> you could have a a really big,
really powerful impact
1241.28 -> that blows away the atmosphere
of a small, fledgling planet.
1245.2 -> Or, you could have a bunch of small
impacts of water rich asteroids
1249.1 -> that are simply contributing
water and volatiles
1252.26 -> and new chemicals to the surface,
1253.56 -> that might help the atmosphere
that's already there.
1256.5 -> When you think about an object
coming to Earth,
1259.14 -> is it gonna land on Earth?
1260.54 -> And, if it does land,
is it gonna be a...
1264.38 -> an erosive event,
1266.32 -> where material is lost
from the Earth?
1268.44 -> Or is it gonna be an accretion event
1270.48 -> where the Earth gains material?
1273.34 -> Well, the devil's in the details.
1276.44 -> Details like the size
of the impactor.
1280.26 -> One study suggests that asteroids
between 60 feet and 3300 feet wide
1287.12 -> add more to the atmosphere
than they take away.
1297.4 -> And speed at the point of impact
also matters.
1302.46 -> Asteroids are orbiting the Sun,
and when they fall towards the Sun,
1306.38 -> they are gaining speed,
they're gaining velocity.
1309.4 -> Imagine dropping a coin
into one of those spiral wells.
1314.18 -> As the coin gets closer
and closer to the middle
1316.12 -> it spins up faster and faster.
1321.2 -> The closer an asteroid
gets to the Sun,
1323.46 -> the stronger
the Sun's gravitational pull.
1327.34 -> And the faster the asteroid travels.
1333.12 -> So, proximity to your star
is a vital factor
1335.44 -> in how intense any impacts will be.
1347.12 -> It's possible that the Earth is the
right distance from its host star,
1351.1 -> so that when an impact happens
the energy isn't insanely high,
1355.24 -> it's just the right amount
that it's the right speed
1357.5 -> to make everything work.
1360.56 -> Supernovas seed the solar system
1363.36 -> with the elements
to build the planets.
1367.28 -> Asteroids and comets
deliver volatile chemicals
1370.52 -> to the surface of the Earth.
1373.26 -> Together, they create
a habitable environment.
1377.5 -> So, we need those impacts to happen
to have life on Earth.
1382.38 -> Disasters created a planet
primed for life.
1387.38 -> But it appears that even more mayhem
and chaos
1391.32 -> are needed to trigger life itself.
1398.76 -> An asteroid tears through
the solar system,
1401.06 -> hurtling through space
at 40,000 miles an hour.
1406.96 -> Its destination?
1408.92 -> Earth.
1410.94 -> Will this space rock inflict
unimaginable damage?
1415.64 -> Or will it bring the spark of life?
1421.9 -> This idea of a of a spark of life,
1423.82 -> we've all kinda seen it in the
Frankenstein movies, right?
1425.86 -> "It's alive."
1427.92 -> This comes from legend,
from myth, from history,
1430.94 -> that there's some sort of a spark
that differentiates
1433.94 -> cold, inanimate matter
from living stuff,
1437.82 -> and, in some sense
it's kind of true.
1443.78 -> On Earth, we think this spark
may have arrived
1446.9 -> over four billion years ago.
1451.78 -> The Hadean Eon was the time
from the Earth's formation,
1455.02 -> about 4.6 billion years ago,
to about four billion years ago.
1459.66 -> It's named after, literally, Hades,
1462 -> so, the conditions on Earth
were literally hellish.
1467.94 -> It was hot and soupy,
a lot of water vapor around,
1470.88 -> high pressure atmosphere,
very intense heat.
1474.64 -> You wouldn't survive.
1475.82 -> The the planet would literally
kill you back then.
1481.88 -> It's shocking,
and I mean really shocking,
1485.06 -> that the evidence of first life
that we have on Earth
1488.06 -> dates to the Hadean Eon.
1490.08 -> This was a terrible place.
1493.04 -> Molten and poisonous and awful,
1495.96 -> and yet, life somehow arose
in all of that mess.
1502.02 -> June 2020.
1504.76 -> Japanese scientists simulate the
conditions of this hellish planet,
1510 -> and then, try to recreate
the spark of life.
1514.06 -> So, what the scientists were trying
to do was mimic those conditions
1517.06 -> and see what would happen
1518.68 -> if you smash a meteorite
into the ocean back then,
1521.12 -> could it produce
sort of the same chemicals
1523.7 -> that we see life using today?
1526.74 -> They use a mix of carbon dioxide,
nitrogen, water and iron
1531.76 -> to replicate the Hadean environment.
1537.04 -> Firing a mini meteor at 2,000 miles
an hour into this chemical soup
1542.68 -> triggers a reaction
between the basic organic elements.
1547.88 -> Creating amino acids.
1551.9 -> We call amino acids
the building blocks of life.
1555.1 -> Really, they're the
building blocks of proteins,
1557.66 -> and life needs proteins to exist.
1559.82 -> But, that's why
they're so important.
1561.7 -> Without amino acids
there's no proteins,
1563.7 -> without proteins,
no life as we know it.
1567.82 -> The experiment proves
that meteorite impacts
1570.8 -> can help build the components
for life.
1576.78 -> But, for these building blocks
to come together and create life,
1581.72 -> we need more.
1583.98 -> It's like, making a cake,
1585.68 -> you could together the oil and the
flour and the butter and the sugar,
1589.64 -> but, if you don't put it in an oven,
you're not gonna end up with a cake,
1591.94 -> you're gonna end up
with something else.
1594.74 -> We thought that the violence
of asteroid impacts
1597.76 -> prevented life from forming.
1602.9 -> Now, we think they could be
an essential ingredient.
1608.66 -> If the asteroid impact is big enough
and fast enough,
1611.06 -> it can punch right through
the crust.
1615.82 -> Then you're getting geothermal heat,
1617.68 -> heat that bubbles up
from the mantle,
1619.92 -> and it is certainly possible
to get an asteroid impact that big.
1624.72 -> Large meteorite impacts
can create hydrothermal vents,
1628.88 -> which some scientists believe
were the cradles of life.
1633.98 -> They provide warm, wet environments
that bring up chemicals
1637.98 -> from deep inside the Earth's crust.
1642.74 -> The perfect place for life to begin.
1647.86 -> As bad as those conditions
seem to us,
1650.8 -> to the molecules that are beginning
to combine and do their thing,
1655.72 -> that was a wonderful place to be.
1657.7 -> It could actually be
that the conditions
1659.12 -> that are best for early life
1661.06 -> might actually be those
just after an impact.
1664.86 -> So, you have sort of this...
this petri dish environment
1668.64 -> in which life could really thrive.
1674.7 -> These vents might be similar to
those we see in the oceans today.
1680.88 -> These hydrothermal vents
provide a little window
1684.68 -> into what conditions
on the primordial Earth
1686.86 -> would have been like.
1688.02 -> And the sort of chemistry that goes
on in those hydrothermal fluids
1692.84 -> seems to be the right kind of
chemistry for creating life.
1700.12 -> Once again, Earth got lucky.
1705.7 -> Impacts that could have
destroyed everything...
1710.66 -> may have helped spark life
into existence.
1715.8 -> I once heard this quote
from Confucius,
1718.78 -> that creation is quiet,
1720.78 -> but destruction is loud.
1724.66 -> Well, these impacts
were both destructive
1727.82 -> but they also may have been
creators.
1731.04 -> Earth leaves behind the Hadean age.
1735.08 -> The planet calms
and life takes hold.
1739.74 -> But disaster is our constant
companion
1742.9 -> as we prepare to face a storm
of deadly cosmic bullets.
1752.44 -> The universe
is a dangerous place for life,
1755.62 -> there are asteroid impacts...
1762.2 -> black holes...
1765.38 -> and exploding stars.
1768.66 -> But, public enemy number one,
cosmic rays.
1774.6 -> Lethal, energetic particles
born in violent events.
1781.24 -> And they come in three kinds.
1783.66 -> Solar radiation is basically
charged particles
1786.3 -> coming from the Sun.
1788.44 -> The second type
are galactic cosmic rays.
1791.64 -> Which are fragments of atoms
that are hurled out from supernova
1796.54 -> and accelerated
to nearly the speed of light.
1802.2 -> And then there's ultra-high energy
cosmic rays.
1808.2 -> We think they come from
all the way outside the Milky Way.
1813.4 -> Because of all of the cosmic rays
going through space,
1816.66 -> the universe is incredibly
hostile to life.
1820.38 -> Cosmic rays are incredibly small,
but travel so fast,
1824.58 -> near the speed of light,
1826.42 -> that they can tear through our DNA
and damage it.
1830.52 -> You're full of DNA, if that DNA
gets broken apart,
1833.46 -> guess what happens?
1834.56 -> That could lead to cancer and death.
1837.4 -> At first glance, these cosmic rays
are the worst things for life,
1842.28 -> they're terrible.
1844.32 -> Despite their frightening rap sheet,
1846.3 -> cosmic rays may have played
a crucial role
1849.2 -> in the evolution of life.
1855.24 -> 2020, scientists at New York and
Stanford Universities
1859.32 -> investigate biological molecules
that have a twin.
1864.6 -> Mirror image versions
called Chiral molecules.
1870.18 -> The concept of Chirality
in chemistry
1871.66 -> is when you have two molecules,
two chemicals,
1874.4 -> that are physically the same,
1875.52 -> they're made of
exactly the same things,
1877.66 -> but their structure is different,
and they're not just different,
1881.3 -> they're reflections of each other.
1882.66 -> It's literally called handedness,
because look,
1885.48 -> here's my right hand
with my thumb over here
1887.3 -> and my fingers over here,
1888.36 -> here's my left hand, with my thumb
over here and my fingers over here.
1891.4 -> I can't wear a left glove
on my right hand,
1893.66 -> there's nothing I can do
to make these guys the same.
1897.56 -> And it turns out this is true
not just for hands,
1900.44 -> but also for a large number of
simple, organic compounds,
1905.46 -> things like amino acids, or sugars,
1908.62 -> which are the building blocks
of all life on Earth.
1914.56 -> Billions of years ago,
early life may have had
1917.46 -> both left and right-handed DNA
and RNA.
1923.32 -> But life chose to use
mostly right handed molecules.
1927.32 -> The reason may have been
cosmic rays.
1934.64 -> When cosmic rays
hit Earth's atmosphere...
1939.18 -> they degrade into even smaller,
sub-atomic particles called muons.
1945.38 -> Most muons spin in one direction.
1949.4 -> So, we have these little muons,
which are very energetic,
1952.28 -> and they're spinning a certain way,
1953.62 -> and when they hit a molecule,
they interact with it,
1957.18 -> they can disrupt it,
they can change it.
1960.36 -> Some scientists believe
these spinning muons
1963.4 -> interact more readily with
right-handed DNA and RNA.
1970.36 -> Triggering mutations.
1973.4 -> Some mutations are beneficial,
but they have to get a chance,
1977.18 -> so, if you have right-handed
molecules and left-handed molecules,
1980.24 -> and they're both being hit by muons,
1982.2 -> the one that's hit more
1983.52 -> gets more chances
to have a beneficial mutation.
1987.56 -> Cosmic rays
may have given right-handed life
1991.26 -> an evolutionary advantage.
1994.56 -> Left-handed life could not compete.
1999.28 -> It's like throwing dice,
if you're trying to get double sixes
2002.42 -> and the left hand
only gets to throw ten times
2004.46 -> and the right hand
gets to throw 100 times,
2007.28 -> more likely to get double sixes with
the right hand than the left hand.
2012.58 -> But the dice don't always land
in our favor.
2016.22 -> 359 million years ago,
Earth's luck ran out.
2021.66 -> And cosmic rays may have
lived up to their reputation
2025.44 -> as the baddest particle
on the block.
2030.38 -> Earth's oceans were teaming
with marine life.
2036.3 -> And, by this period as well,
2038.3 -> plants had started to colonize onto
the continents and land masses,
2042.64 -> attracting animal life,
insects, millipedes,
2047.38 -> and it's in this environment
that Earth experienced
2051.56 -> one of the greatest mass extinctions
in the history of life.
2059.52 -> Something killed off 97%
of all vertebrate species.
2065.5 -> We call this wipe out
the End-Devonian Extinction.
2074.3 -> One possible explanation?
A supernova.
2079.22 -> When some dying stars explode,
they fire out cosmic rays.
2085.32 -> This radiation bombards
the upper atmosphere of the Earth
2090.34 -> and drives the chemistry of nitrogen
turning into nitrogen dioxide.
2095.44 -> A gas which itself can reacts with
the ozone layer and destroys it.
2101.48 -> Without the protective ozone layer,
2103.58 -> ultraviolet radiation from the Sun
bombards Earth.
2109.32 -> Radiation rains down for
thousands of years.
2114.24 -> Damaging the DNA
of plants and animals.
2121.3 -> Many species die out.
2126.22 -> The End-Devonian mass extinction
mostly affected marine life.
2131.42 -> This is where we see
the greatest percentage of deaths.
2136.28 -> The oceans, once populated by fish
the size of school buses,
2142.2 -> now host fish
no bigger than a sardine.
2147.26 -> These smaller fish
reproduce quickly,
2151.28 -> in the challenging environment
they adapt
2153.54 -> and diversify faster
than larger species.
2158.18 -> Mass extinction's not only
wipe the slate clean
2160.64 -> and provide other animals
and other life forms an opportunity,
2165.56 -> it creates a sort of chaotic
and complex environments
2169.3 -> that drives natural selection
and evolution.
2175.58 -> If a supernova was to blame
for this extinction event,
2179.32 -> scientists believe that the culprit
was 65 light years away.
2186.28 -> Any closer, and Earth's luck
would have run out completely.
2191.56 -> It seems the existence of life is
always balanced on a knife edge.
2196.5 -> One exploding star goes
off a little bit too close to us...
2201.58 -> and we are all destroyed.
2206.48 -> So, there's this wonderful balance
between just violent enough
2210.36 -> and too violent, and we have been
lucky enough to dance on that edge
2214.18 -> for four and a half billion years.
2217.36 -> This mass extinction
reset life on Earth,
2220.62 -> and paved the way
for four legged creatures,
2223.5 -> our distant ancestors.
2229.32 -> Cataclysmic events go hand in hand
with human evolution.
2234.54 -> Some knock this back,
2236.58 -> and others,
2237.6 -> like the event 66 million years ago,
gave us a push forward.
2244.7 -> 66 million years ago, a massive
asteroid crashes into the Earth.
2252.92 -> It triggers a huge extinction event,
2256.18 -> without it,
humans may have never evolved.
2260.8 -> At this time in Earth's history,
we had these enormous plants
2264 -> and gigantic insects
2266.08 -> that actually would have been
incredibly terrifying
2268.1 -> if we saw them today.
2271.92 -> Terrasaurs sailed through the air.
2274.7 -> Huge marine reptiles
dominate the oceans.
2277.88 -> And the T-Rex
is the king of the world.
2284.78 -> Then, a glowing object
appears in the sky.
2293.76 -> I'm sitting on the beach, what was
then gonna be the Yucatan of Mexico,
2298.76 -> enjoying a drink with a,
you know, little umbrella in it.
2301.7 -> But, up there in the sky,
all of a sudden,
2304.9 -> approaching me at 40,000 miles
an hour, is Mount Everest,
2309.84 -> glowing thousands of times
more intensely than the Sun,
2314.16 -> and it's just seconds away
from dropping on my head.
2318.72 -> A six-mile wide asteroid...
2322.88 -> slams into the Earth.
2330.76 -> The impact throws trillions of tons
of rock and dust into the air.
2338.02 -> The rocks heat up
as they fall back to Earth.
2342.12 -> Setting the planet on fire.
2348.7 -> That beach holiday suddenly turns
into absolute nightmare.
2353.88 -> The impact also throws up soot,
choking the atmosphere.
2359.84 -> Now the skies are blotted out
by all these materials,
2363.02 -> so, the Sun is no longer shining
brightly on the surface.
2368 -> Planets need sunlight
to photosynthesize.
2372.74 -> Without this vital energy source,
many species die out.
2379.8 -> With their food source gone, plant
eating dinosaurs starve to death.
2385 -> Followed by their predators.
2388.14 -> It was a huge disruption
to all of life on earth.
2391.16 -> The dinosaurs have been around
for 160 million years at this point.
2395.14 -> That's no small amount of time.
2396.92 -> And, in one event, they're gone.
2399.9 -> Again, the dice roll
is in our favor.
2404.04 -> Most dinosaurs become extinct,
2406.08 -> paving the way
for the evolution of mammals.
2410.8 -> Leading, eventually, to humans.
2414.96 -> Without the asteroid impact,
we wouldn't be here.
2419.78 -> As a furry primate on this planet,
I kinda like the KPG impact, right,
2422.84 -> I'm here because of it.
2424.12 -> We all are.
2427.08 -> Some plants benefited
from the asteroid strike.
2431.74 -> To learn how plants changed
after the impact,
2434.72 -> Smithsonian scientists examined
thousands of tropical plant fossils
2439.8 -> from the time of the die off.
2444.18 -> This disaster opened the way
for new types of plants to develop.
2449.88 -> It transformed the plant kingdom,
2452.92 -> producing a richer and more diverse
global ecosystem.
2457.06 -> Before the asteroid strike,
conifers and ferns
2460.8 -> dominated the tropical forests
of South America.
2464.9 -> But, afterwards, falling ash
from the impact enriched the soil,
2469.84 -> and fast growing,
flowering plants took over.
2475.18 -> The impact was very hard
to recover from,
2478.1 -> but it actually opened
the opportunity
2480.18 -> for a greater diversity
of plant life,
2482.16 -> which ultimately
has benefited us as humans,
2484.84 -> because it has allowed us to have
more food sources.
2489.7 -> This new world order
eventually gave rise
2492.72 -> to the modern Amazon rain forest,
2495.06 -> home to 10% of all species on Earth.
2501.96 -> It really destroyed and remade
our entire environment,
2506.7 -> the world grew back,
of course it did, here we are,
2508.94 -> but it changed everything.
2511.98 -> And, another age
maybe just around the corner.
2516.76 -> We should absolutely expect that
at some point in the future,
2521.12 -> and I'm not saying
you should lose sleep over it,
2524 -> but, at some point, there will be
another mass extinction.
2531.96 -> Maybe that will be the end
of our days.
2534.94 -> So, an intriguing question is,
2536.96 -> what might come after humans
on planet Earth?
2542.78 -> Catastrophe may be
the universe's recipe for life
2546.86 -> throughout the cosmos.
2549.18 -> One that every planet must follow.
2552.98 -> Looking at our own history,
life thrives on catastrophes,
2557.08 -> we need these disasters
for evolution to work.
2560.84 -> So, hopefully, and I hate
saying this, I know how it sounds,
2564.74 -> hopefully, these other planets
have had terrible disasters as well.
2569.74 -> Think about the word disaster,
it means bad star,
2572.8 -> it means that something has gone
wrong, something that's dangerous.
2576.1 -> We are children of disasters.
2580.88 -> There's no way you'd get us
without planets colliding.
2585.14 -> Without asteroids and comets
streaming through the atmosphere.
2592.7 -> Without even stars
exploding and supernovas.
2599.1 -> You are a child of that violence,
that's part of the environment
2601.98 -> that we grew up in,
in a cosmic way,
2604.7 -> and I think that is
tremendously beautiful.
2607 -> Finesse Media Services
Source: https://www.youtube.com/watch?v=l9048cL5l5M