there was darkness . And then, bang. Giving birth to an endless
expanding existence of time, space, and matter. Every day, new discoveries
are unlocking the mysterious, the mind-blowing, the deadly
secrets of a place we call the universe. What would happen if our
moon suddenly disappeared? Global tsunamis decimate
coastlines around the world as ocean waters surge toward the
gravitational pull of the sun. Sea currents shift,
changing weather patterns and destroying food supplies. Eventually, Earth's axis tilts
wildly, turning the poles into tropical jungles and the
equator into frigid wastelands. New species emerge,
while others go extinct. Our planet becomes
unrecognizable. The day the moon was gone. [music playing] The moon is a barren,
lifeless rock. But it plays a
surprisingly important role in the story of life on Earth. How important? Let's remove it from
the sky and find out. Strange things start to
happen and almost immediately. People on the coast are the
first to notice the change. This would probably create
something like a tsunami. A tidal wave, which would
be very dramatic, indeed. NARRATOR: It's well-known that
the moon controls the Earth's tides. As it orbits around us, its
mass tugs our oceans toward it, causing a tidal
bulge on the side of the planet nearest the moon. And through a strange quirk
of gravitational physics, it forms a second bulge
on the side farthest away from the moon. Few people realize the
sun also plays a role in governing the tides. But because it's 400 times
farther from us than the moon, its gravitational
influence on the oceans is relatively small, about
one third of the total effect. [music playing] But with the moon
out of the picture, the sun is now in control. With the moon up here, its
gravitational pull is, sort of, pulling a dome of water. There's a big bowl. And then imagine you just
snipped the cord and the water had to flow back out. NARRATOR: The water rushes
toward the gravity of the sun, in a massive global tsunami. The force of the
waves depends on where the moon is in relation to
the sun when it disappears. If the moon vanished at
full moon or at new moon, that's when the moon is lined
up with the Earth in the sun. NARRATOR: The lunar
tidal bulges would shrink to solar tidal
bulges in the same spots. And the extra water
from the lunar bulges would quickly flow to
other parts of the globe. But there's an even more
dramatic possibility. If the moon vanished
when it's at quarter moon, either first quarter
or last quarter, then the moon's tidal bulge
is not in the same place as the sun's tidal bulge. And so, I expect you would see
a very quick motion of Earth's oceans from the lunar tidal
bulge to the solar tidal bulge. [music playing] NARRATOR: Some experts believe
this more drastic lateral shift in ocean water would blast
coastal spots around the world. The powerful pulses would be
similar to the 2004 Southeast Asian tsunami. Except the waves would
cause even more death and destruction, since
they'd be worldwide. Two massive East to West
and West to East waves would be initiated on
opposite ends of the Earth. A seaside city like Miami
would be pummeled by a 50 foot wall of water that would
destroy most coastal buildings. And sweep across the entire
width of Southern Florida, putting 9 million lives at risk. But with such a
Titanic shift of water, could there be other
unpredictable results? One can imagine that perhaps,
the East-West or North-South motion of that water could
disrupt the currents. The gulf stream carries warm
water from the Caribbean up to Great Britain. And it helps keep Great
Britain a lot warmer than it, otherwise, would be,
considering how far north it is. Climate is a very
delicate system. And you tweak one part of it
and another part responds. And then one can imagine
that food productivity and the overall way of life
would be dramatically altered if it were cooler
in northern Europe. The Sahara Desert
is a great example. It's a place that used
to be green and lush and now is completely a desert. Having changes with
climate can really have impact on our survival. NARRATOR: But the biggest
impact on our planet would be the changes to Earth's
steady tilt. A unique feature that gives us our
four regular seasons. The thing that locks our
planet's tilt to about 23.5 degrees so consistently is
the presence of the moon that acts as a large stabilizer. If we don't have
the moon anymore, we may get into a regime
that's much more like Mars. And Mars, instead of being at
a stable 23 and 1/2 degrees, goes through wild
variations of the tilt. A varying from maybe as low
as 15 degrees on the low side, all the way up to something
like about 75, 80 degrees on the high side. NARRATOR: Without
the moon, our axis begins fluctuating erratically
over several thousand years. The gravitational pull
from other planets in the solar system starts
wreaking havoc on Earth. Our stable seasons
shift dramatically, as different parts
of our planet tilt radically toward the
sun during some periods and away at others. Soon as you get
rid of the moon, you're stuck with this
radical tilting of the axis, back and forth. And, therefore,
radical climate changes that don't happen today. [music playing] NARRATOR: Earth becomes a
very strange world, as mankind struggles to adapt and survive. If we go to a situation
where we don't have that stabilization,
those very small changes become very, very big. We may go to a situation
where the ice becomes stable over the Tropics. Imagine jungles and
forests in Antarctica and ice sheets and
glaciers in Central Africa. The tilt would vary on
timescales of a few 100,000 years. These are timescales of Ice
Ages coming on the Earth. We know how much of
an impact that had. And humanity at a hard
time adjusting to those changes as we came out
of the last Ice Age. It's very difficult to predict
exactly what would happen to humans. Because we're not
sure how rapidly we're able to adapt to
radically-changing environments. NARRATOR: And if our moon
disappeared permanently, life in the sea and
on the shore would be drastically transformed. Sharks would lose
their hunting prowess, unable to track the
schools of fish swarming above them in the moonlight. Crabs, used to mating
at extreme low tides, become disoriented at
the loss of lunar phases. Grunion that lay their
eggs during a high tide and full moon suffer
reproductive disruption. Even primitive aquatic plant
life would be affected. Many species would spend
their evenings on the surface interacting with moonlight. The moon comes out, the
algae are moving up. And they're followed by
all of the organisms that eat the algae and the
organisms that eat them. So the whole ecology of the
ocean is tuned to light. And all of these organisms
will be completely disrupted. None of their ecology will
work because they won't have the usual sensing signals. [music playing] NARRATOR: Millions
of people would suffer from food shortages. And coastal economies
would be devastated by the worldwide crash in
marine life populations. I would liken it to one of us
suddenly waking up one morning and discovering we
were blind or deaf. That would be a chaotic thing. NARRATOR: An Earth without the
moon is a rudderless planet. Highlighting just how
critical this big rock is to sustaining life here. [music playing] There are over 150 moons
in our solar system, but Earth's moon
is truly unique. Our moon is unlike
any of the other moons in the solar system. It is huge compared to Earth. It's about a quarter
of the size of Earth. And you don't see that in
any of the other planets. Because the moon is so
big relative to the Earth, it's as if we're really
in a double planet system. There's a crude way to think
about the effect of the moon stabilizing this axial
tilt of the Earth. If you notice
tightrope walkers will carry this long pole and that
gives them more stability. Because there's mass out there
on the end of the pole and. It's harder to
fall off the line. So it's that same kind of thing. That the mass at a distance
can affect the stability of the system. [music playing] NARRATOR: But the moon has
not always been by our side. There was a time early
in Earth's history when there was no moon. A period when our planet
was a strange place, with eight hour days
and a modern landscape too harsh for life. And then, suffered the
most violent collision in its history. It's hard to imagine that there
was a time when our Earth did not have a moon. Our planet was formed 4
and 1/2 billion years ago by accumulating and fusing
large amounts of debris in the early stages of
our volatile solar system. During that early period,
our moonless Earth was a monstrous stew of
flowing lava, molten rock, and liquid iron. Its atmosphere was filled
with carbon dioxide, belched from the
bowels of the Earth's. Thick, heavy, and
uninhabitable for life. There was almost
nothing on the planet. This was a nasty place to be. Lots of things were condensing. It was an extremely hostile
place, even to rock chemistry. So the rocks were melted. Everything was a mess. [music playing] NARRATOR: Our original
Earth without its moon was an unrecognizable world. The early Earth was
a really hot place. In fact, that era of the
Earth is called the Hadean, like Hades. Well, because it was really hot. There was a tremendous
amount of volcanism and a lot of impacts coming in. There was probably, a lot of
lightning and out-gassing, both from the volcanoes
and from steam. [music playing] NARRATOR: The stability
of our early solar system was not much better. It was created out of a huge
disk of gas, debris, and dust that swirled around
the newly formed sun. Our early solar system was
kind of like a roller derby. Everybody was generally
going in the same direction, but there was a lot of chaos. There was a lot of
clumping and accreting and things getting
flung to the inside and crossing lanes
to the outside. People all spilling
over each other, mashing up in the corner. It was a real mess. [music playing] NARRATOR: Without the moon, we
can only guess at the Earth's early tilt and rotation rate. That would have been determined
by the multiple glancing collisions from the
innumerable asteroids and proto planets that ricocheted
throughout our early solar system. If you kind of average
over the solar system, you look at all the planets
and the big asteroids and make a bell curve
of rotation speeds, it looks like the
typical rotation speed might be eight hours. Something like that. So we could make a
guess that that might have been the likely rotation
speed before the moon was formed. [music playing] NARRATOR: Then about 10 million
years after our moonless Earth began taking shape, there
was a massive collision. Now widely accepted
by astronomers, the giant impact theory says
that a Mars-sized planet collided at an oblique angle
at 25,000 miles per hour with Earth. The impactor blasted more than
70% of the Earth's molten crust into space. A giant whirling arm made
up of 5 billion cubic miles of blazing rock and light
metals was launched into orbit around our planet. The gravity of the larger chunks
began pulling smaller particles towards them. Within one year, it
coalesced into our moon. [music playing] The only materials that were
blown out from the Earth where the crustal rocky material. And that's what the
moon's made out of. And, in fact, if you
go to any other place in the solar system-- for example, Mars or
look at meteorites that come from the asteroid belt-- there are certain ratios of
the different types of oxygen. That ratio in other
parts of the solar system is very different than
what we see in the Earth. Now we fly to the moon. We get the moon rocks. We bring them back. They have exactly the
same oxygen isotope ratio as the Earth. So that material came
out of the Earth. And that fits this idea
of an impact theory. NARRATOR: The energy released
in the giant collision equaled a force of 6
trillion atomic bombs. That's 1,000 atom
bombs for every person in earth's current population
of 6 billion people. [music playing] The impactor planet that
hit Earth was thought to have formed in an
area of our solar system called the Lagrangian points. These are regions
60 degrees either ahead of or behind the Earth,
but at a similar distance from the sun. NARRATOR: Debris can stay
fixed in the Lagrangian points for tens of millions
of years, locked between the gravitational
influence of the sun and Earth. But eventually, something
knocked the impactor off its fixed course. That something was Jupiter. Every time Jupiter
passed by us in its orbit, it would be giving a little
tug to this impactor planet. And each little tug
wouldn't be very big. But if you think about,
for example, having a car that's stuck in a ditch
or stuck in a snowbank. How do you get that car
out of the snowbank? Well, the way you do
it is you rock the car. You push it a little
bit, it comes back. Push a little bit more, it
comes back a little farther. And this way, with a
bunch of little pushes, you eventually free it. And that's exactly what Jupiter
did to this impactor planet. And once it gets away
from the Langrange point, it's no longer stable
and it's doomed. It's eventually going
to collide with Earth. [music playing] NARRATOR: After the
giant cataclysm, the inner part of the
whirling arm of ejected debris forms a clump that consists of
materials from the impactor's iron core. That heavier clump
re-collides with Earth and is absorbed into
our planet's center. The giant impact was
really, the biggest thing that ever happened to Earth. What we have now is
a core and a half. That makes our planet
denser and our gravity stronger than it
would be, otherwise. NARRATOR: The larger
molten core takes longer to cool than the Earth's
original core would have. Heat is constantly
pushed up and through the thin crust of the
Earth, creating fissures. It's possible that this
larger core helped create the sustained plate
tectonics system that formed our continents. A unique planetary feature
in our solar system. As an example, Mars
was much smaller. It cooled much quicker. And so it has no crustal plates. NARRATOR: Most critically,
the collision knocks the Earth onto its current axial
tilt of 23 and 1/2 degrees. And speeds up its rotation from
eight hours to just five hours. Within a year, the moon forms
roughly 14,000 miles away from Earth, significantly
closer than its current distance of 234,000 miles. You've got this immense moon
in the sky, 15 times as big as the present moon. So think about this thing
rising and rising and rising, until it fills up a pretty
big chunk of that evening sky. And imagine it being red
because it's full of this molten lava around the surface. And imagine that
looming over your head. It's mind-boggling. NARRATOR: The early moon's
gravitational pull on Earth is roughly 200 times stronger
than today because of its much closer distance. Though no oceans exist
yet, the lunar tidal forces are 3,400 times more powerful. They lift and drop large
crusts of molten rock to more than half a
mile high twice a day. Our early planet's
axial tilt stabilizes due to the moon's formation
and its mass acts as an anchor. But the Earth's spin begins
slowing because the moon's gravitation creates a tidal
bulge around our planet's midsection, causing a drag
on the Earth's rotation. Let the Earth be this green
balloon and here's the moon. If the Earth weren't
rotating, the tidal bulge would point directly
toward the moon. But the Earth is
rotating pretty quickly. So, in fact, the
tidal bulge tends to be a little bit ahead of
the direction toward the moon. That means the moon's gravity
is pulling back on the Earth's bulge a little bit. Retarding its rotation
ever so slightly. [music playing] NARRATOR: But the
tidal bulge on Earth also has a reactive
force on the moon. This tidal bulge pulls
the moon ahead in its orbit. It's constantly trying
to tug the moon faster. But the moon doesn't want
to go faster in its orbit. Instead, what happens, if you
imagine throwing a slingshot and swinging faster. It wants to go out. And that's what the moon does. It goes outward because
it's being tugged faster in its orbit. So gradually, over
the years, the moon is moving farther
and farther out. [music playing] NARRATOR: The complex
gravitational dance between the two partners is
now pushing the moon away from Earth at a rate of 1
and 1/2 inches per year. Over billions of years,
the moon's recession has slowed the Earth's rotation
from five hour days to our 24 hour day today. The whole idea of this
rotation of the Earth being influenced by the
moon is a little bit like what you see when a
figure skater is spinning. And when she pulls her
arms in close and spins, she spins faster. And she throws her
arms out to slow down. And this is all what the
physicist would call angular momentum. But it's the same idea. As the moon moved out, it's kind
of like throwing those arms out and that slows down the
rotation in the little system. [music playing] NARRATOR: But what if the giant
impact had never happened? The changes to Earth
would be even more drastic than if the moon now
suddenly disappeared. Today, would we recognize an
Earth that never had a moon? And would humans even exist? If the moon
disappeared instantly, Earth would undergo changes
like possible tsunamis, a shift in ocean currents,
sea life extinctions, and eventual massive
climate swings. But if the moon
had never existed, Earth would be unrecognizable
to anyone today. Without the
moon, life on Earth would probably look
quite different. In particular, humans might well
never have come into existence. [music playing] NARRATOR: About 150 million
years after a moonless Earth forms, 4 and 1/2
billion years ago, it moves out of its hot molten
phase and begins cooling. The day is only about
eight hours long. If we had an eight
hour rotation period, we'd have four hours of daylight
and four hours of night. And nights would be totally
black, if we don't have a moon. NARRATOR: Once cooled, our
planet is temperate enough to retain water. Heat escaping from Earth's core
drive steam and carbon dioxide beyond the surface,
creating a thick atmosphere. And over a period of time--
many, many, many, many years-- all that atmosphere would
have collapsed back out. And then as it
cooled, the oceans would have formed in
torrential rainstorms. NARRATOR: Icy asteroids
continually pummel the planet, bringing in another
large source of water. With a smaller
cooler molten core, there are probably,
no plate tectonics. And, therefore, no large
mountains and huge ocean basins. Water soon covers most of the
planet's more uniform crust. We certainly would
have a higher sea level than we have today. Less continental area. And that would be
a different world. Our blue marble
would be even bluer. NARRATOR: Ironically,
even with all that water, the early moonless Earth
would have smaller tides. Determined only by the
gravitation of the sun, they would be just one third
the size of our current tides. The range between
high and low tide would remain constant
throughout the year. And would occur at exactly
the same time each day. And that means the
intertidal regions would have been narrower. Probably leading to less
diversification of life. And perhaps, even impeding
the progress of life from the oceans to the land. Because it's in the intertidal
regions where creatures had to develop the ability to
survive both in the water and on land. NARRATOR: With an
eight hour day, just four hours
of light followed by four hours of moonless
black, the early Earth spins three times
faster than today. The winds howl due to the
aerodynamics of Earth's quicker rotation. Jupiter, for example,
is a giant planet that spins very rapidly. It has a 10-hour spin period. And it's got ferocious winds
in its upper atmosphere. Hundreds of miles an hour. And incredible storms,
like the Great Red Spot, which has been
around for centuries. Now Earth probably would be
spinning more rapidly than it is now. And that would generally lead
to stronger winds and more violent hurricanes
and other storms. [music playing] NARRATOR: Early Earth's
fast spin results in another important
side effect. The rotation of Earth's core,
particularly the molten part of the core, is
believed to be what generates our magnetic field. And so if the Earth
rotates three times faster, the magnetic field is
three times stronger. NARRATOR: The enhanced magnetic
field over the moonless Earth more effectively deflects high
energy solar flare particles towards the Earth's poles,
resulting in larger more spectacular auroras. But by blocking
the solar flares, not as much radiation zaps
life in the lower atmosphere. Decreasing mutations
that drive evolution. A stronger magnetic field
might have slowed the rate at which life evolved on Earth. [music playing] NARRATOR: Without the
moon, the developing Earth suffers intense
climate volatility. Over many periods, each
lasting several million years, the Earth's axis is
pulled and pushed by the sun and other planets. Without the stabilizing
influence of the moon, conditions would have paralleled
what happened to Mars. What we've learned in
the last 15 or 20 years is that Mars has a very
unstable axis because it has no big moon. And when we look at
Mars, and we can actually see on the surface of
Mars, geological features that formed under
very different climate regimes when the polar
axis was tilted over. On Mars, we actually see these
features like the dry river channels and glacial
deposits and other features. Ice close to the equator. And so the big
realization was, oh, yeah. The climate has been
changing on Mars. And this explains that we're
seeing holder features. [music playing] NARRATOR: Like the Red Planet,
a moonless Earth's axis would tilt wildly. Turning our planet topsy-turvy. Our axis, over a period
of millions of years, would wobble chaotically. It would sometimes be vertical. It would sometimes be
close to horizontal. When it's vertical,
then the whole Earth might be kind of a
tropical paradise. When it's horizontal,
you could actually have the poles pointing
towards the sun and the poles actually getting jungles. So you would see very big
changes in Earth's climate as a result of this chaotic
wandering of Earth's axis. And this would make it more
difficult for life to flourish. Because it would
constantly have to adapt to different conditions, to ice
ages and to extremely hot ages. [music playing] NARRATOR: So what
would life on Earth look like today if we
had never had a moon? Short days, high winds,
and other changes could produce a freakish
world, with creatures that looked like
they're straight out of science fiction. The moon was formed
billions of years ago, when a planet-sized
asteroid crashed into Earth. But what if that violent
collision never happened? If the moon never came along
to stabilize our planet, Earth would be an alien place. The spin of early
Earth was very fast, with about four hours
of daylight followed by four hours of darkness. Over billions of years,
the sun's gravity and tidal friction would
lengthen that eight hour day to 12 hours. But this is still twice as fast
as the current Earth spins, which makes for some
extreme weather, including devastating
storms and high winds. [music playing] If the moon hadn't
formed, you certainly get a wildly different
environment on the Earth. With a faster turning Earth,
you get more jet streams. You get more
turbulence, probably. Maybe bigger storms. More lightning because
of the friction of the different
masses of air moving. In some places, the winds
could reach 100 or 200 miles an hour. There would also be
stronger hurricanes. And the Earth would have larger
waves battering the coastlines. NARRATOR: And without the
moon's stabilizing effect, the rapidly spinning Earth
tilts back and forth. Over hundreds of
thousands of years, our planet suffers the ravages
of ever-shifting climate because of the erratic
changes in axial tilt. As different regions
are blasted by heat, then covered by ice,
again and again. And without the moon,
there is another layer of axial instability. Even though today's Earth
is stabilized by the moon, there is still a wobble to
the Earth's rotation, known as procession. Earth's tilt is
23 and 1/2 degrees. But over a period
of 26,000 years, it goes through conical
variations like this. NARRATOR: And if the
moon had never formed, this wobbling would be
much more unpredictable. If we didn't have
the moon, the Earth would precess much more slowly. And this is one cause
for chaotic variations in the axial tilt. A slower
precession of the Earth would lead to a much more
unstable axis of rotation for the Earth. [music playing] NARRATOR: Without the
moon, Earth's axis today would be like the
slower spinning top. Precessing, gyrating,
and wobbling in ever-larger conical circles. Right now, 26,000
years, a very stable zone. You get it going slower so it's,
maybe 40,000, maybe 50,000, maybe 60,000. Then you hit the chaotic range
and then everything goes wrong. NARRATOR: With the more
forbidding and shifting climate, evolution
on a moonless Earth varies between
bursts of adaptation and violent extinction. Bizarre lifeforms mushroom. Plant species are vulnerable,
as they don't have the mobility to stay ahead of
speedy climate change. And complex life
forms like humans probably wouldn't
stand a chance at all. The variations
in climate would be extreme and rather rapid. And it would probably, make it
difficult for complex creatures to evolve. Because most complex creatures
can't evolve very quickly to changes in their environment. NARRATOR: Instead,
primitive organisms would predominate and endure. Bacterial life is able not
only to adapt more quickly, but also to withstand
more extreme environments. We see bacteria under the deep
ice cores of the Antarctic or Greenland. And we see bacteria that
live in steaming boiling pots in Yellowstone. [music playing] NARRATOR: If complex
life were to evolve, it would look very
different due to short days, high winds, and other
features of a moonless Earth. It would be much more
hostile than it is now. You would see that all
of these winds and all of the noise and
all of the clouds, moving from water to life
on land would be very tough. We might see shorter lifespans
because things are going on faster. During the day, there
will be a limited time to metabolize and gain
energy and do things. Organisms would have to
be a little more clever. NARRATOR: Evolution would
favor short, stout creatures. And plant life that could
withstand ferocious hurricanes. Jungles wouldn't
exist, since they need wind barriers to flourish. And there probably wouldn't
be any creatures swinging from branch to branch,
due to stubbier plant life and high winds. I would expect that creatures
generally wouldn't be as tall because they'd have a harder
time holding themselves up. And trees with
shallow root systems wouldn't become very tall. Palm trees, for
example, probably wouldn't survive too well. [music playing] NARRATOR: The constant gusts
would push other adaptations. Sailing, know maybe membranes
that lets you take off and leap through the air. NARRATOR: And the perpetual
gale-like conditions would create an
exceptionally loud planet. If animals made
noises to communicate, they'd have to be very different
from the constant shrieking wind sounds. The use of sound at
wavelengths that are not the sound of the
background noise. If you have a receptor that
just zeros out that noise, we might be able to speak like
this and be heard perfectly. We might all be sopranos. And have ears tuned
to a different pitch. NARRATOR: Or more visual cues
might be developed to cut through the audio overload. Creatures might
develop extra limbs to not only shield
themselves from the wind, but also use their
appendages to communicate. Like sailors using
semaphore signals. Perhaps speech
would not develop. So maybe other forms
of communication, whether color changes,
expression changes, hand languages. Who knows? NARRATOR: Even today,
many of Earth's beings such as fireflies, squids,
krill, and jellyfish communicate by changing
their body colors. Because of the dark
nights, creatures might also develop enhanced
vision and sensory systems. Similar to the night vision
goggles and infrared displays used by the military. The interesting possibility
is that life might be able to develop sensors that
were so good that they could actually sense starlight. And this would be
something colossal. NARRATOR: It looks and sounds
like a rough and too tough world. Unfit for human habitation. Luckily, when the moon formed,
it created the conditions for people to
develop and prosper. But our moon is also
moving farther away from Earth every year. Does that mean there will be
another time in Earth's future without the moon? 4 and 1/2 billion years
ago, the young Earth was a hellish, molten place. Unfit for life. So then, how did a violent
collision by an object the size of Mars soon after
the Earth's formation create the conditions for
the complex life we're part of today? The body blow to Earth knocked
our planet to its current tilt and the formation of
the moon kept it there. The mass of the moon
out there, what it's done is it's prevented the
tugs of the other planets from causing the Earth
tilt to change too much. So we've provided a
real stabilizing effect on our climate because of that. NARRATOR: The collision also
created a chain reaction of forces that set
the stage for life. When the iron cores of
the two planets combined, it created a larger
core for the new Earth. The collision also knocked
off much of the Earth's crust. This combination, with large
amounts of heat pushing up from a giant core
through a thin crust, likely created the conditions
for sustained plate tectonics. The movement of these plates
formed mountain ranges and deep basins. And the resulting
volcanic activity spewed out the gases that
created our atmosphere. Water eventually settled in
the basins, creating oceans. Leaving continents
of land above. But life still had a
tough time getting started in the early days of Earth. [music playing] For the first
1/2 billion years of the Earth's and
the moon's existence, they were bombarded by debris
that was still finishing up the formation of
the solar system. So even if primitive life-- microbes and bacteria-- had
formed in the first few million years, they might easily
have been wiped out by these giant things
crashing into the Earth. Now we have evidence
for life dating back to 3.8 billion years ago. That's shortly after the end of
the era of heavy bombardment. [music playing] NARRATOR: By then, due to tidal
friction between the Earth and moon, the moon had
moved slightly farther away from Earth. And Earth's rotation had slowed
to roughly a 10-hour day. But since the moon was still
much closer than today, the tides and Earth's early
oceans were humongous. The tides went way inland
and poured back out to sea. Twice a day, you'd get
big gulf of water in. And when it drained
back out, it carried a lot of minerals and soils
and other parts of the Earth's crust back out to sea with it. So there was this constant
erosion and scrubbing of the land. Certainly, a unique
environment that might have been just right
for life to develop. NARRATOR: The area between
high and low tide, known as the intertidal
region, was enormous. High tides would rush hundreds
of miles inland, then back out a few hours later. During the low tides,
molecular strands began forming in some of the
endless miles of tide pools. What happens when
water evaporates? The H2O molecules go away
and everything else is left. So the organic
sludge in the pool gets more and more concentrated
as the water evaporates. So this was the idea that life
formed in these little pools. [music playing] NARRATOR: Around 570
million years ago, almost 3.9 billion years after
the giant impact, Earth's ocean life begins moving onto land. Giving birth to complex species. The bigger the
intertidal regions, the greater the resulting
diversity of life. Because you can have species
that live in these environments that are sometimes exposed
to the sun and sometimes underwater. [music playing] NARRATOR: Over
billions of years, our Earth seems to have reached
a perfect equilibrium that has allowed for the evolution
of a diverse, intricate, and fragile ecosystem. There are some
climates that are too uniform in those
seasonal changes and so on and don't lead to
life because there's no environmental stress. And, on the other hand,
climates that are too variable, where the seasons are
changing all the time and you're getting hit by an
asteroid every million years, planets like that would
probably try to form life, but they couldn't get it going
because things would change too fast. So maybe there is
a situation that's just right in the middle. And maybe the Earth/moon system
is somewhere in that range. Which has fostered not only the
formation of primitive life, but the evolution of that
life into folks like us. NARRATOR: But though our
moon stabilizes things, it continues to recede from
us, at a rate of an inch and a half per year,
while it slows our spin. Scientists estimate that we're
adding two seconds to our day every 100,000 years. A billion years
from now, our days might last 26 hours,
rather than 24 hours. Which is great if you're
a procrastinator like me. You could always use more time. [music playing] NARRATOR: So what will happen
to the unique Earth/moon partnership that made
life on Earth possible? Will the moon eventually
just drift away, out of Earth's
gravitational influence? The rate will be so slow that
it won't be a very big effect. And long periods of time will
pass without much change. So long that we will have had
time for our sun to run out of fuel and become a red giant. At that time, the
Earth will be destroyed and so will the moon
at the same time. We'll all get baked together. [music playing] NARRATOR: So maybe
it's comforting to know that 5 billion years from
now, on the day the Earth faces its end, we
won't be alone. Our anchor in the
sky will be there. The glowing orb that made
advanced life on Earth possible.
