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♪
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Narrator: The earth is taking us
on the ride of our lives,
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00:00:08,943 --> 00:00:13,112
hurtling through space
in ways we never imagined.
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The earth is extremely dynamic.
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It is spinning on its axis.
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It's whirling about the sun.
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It's corkscrewing
throughout this galaxy.
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It's just never a dull moment.
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It's like doing a waltz
on top of a carousel
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00:00:27,028 --> 00:00:29,795
that's on top
of a high-speed train.
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Narrator:
Now we're unlocking the secrets
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00:00:32,566 --> 00:00:37,202
of our planet's voyage and
discovering that earth's journey
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00:00:37,204 --> 00:00:38,670
affects us all.
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♪
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We see evidence of this motion
everywhere we look,
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not just in the motions
of objects in the sky,
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but in the land
and the seas themselves.
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Life on earth
wouldn't be the same
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if we didn't find ourselves
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in this dramatic environment
in space.
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♪
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Narrator: But the ride
can be dangerous...
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♪
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[ Explosion ]
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Plunging our planet
into the deep freeze...
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[ Ice cracking ]
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Putting us in the path
of supernovas,
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♪
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Pulling earth and the entire
galaxy toward the unknown.
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The galaxy is traveling
through space.
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Where is it going?
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It's an area of really
cosmic mystery.
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Narrator: So strap in for
earth's cosmic journey.
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[ Electricity crackles ]
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[ Explosion ]
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captions paid for by
discovery communications
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♪
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We are earth's passengers
as our home planet
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travels through the cosmos.
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♪
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To us, everything seems calm.
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Nothing could be further
from the truth.
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Contrary to what you might think
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00:02:07,228 --> 00:02:09,061
just based on your
everyday experience,
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the earth is actually
hurtling through space
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at amazing speeds
in a lot of different ways.
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[ Crickets chirping ]
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Even just the motion of the
stars through the sky at night
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gives you a clue that the earth
is not sitting still.
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♪
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The earth is spinning
at every moment,
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and we can see this most clearly
in the fact
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that we have day and night.
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Narrator:
We might not think about it,
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but our lives are tuned
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to earth's journey
as it spins through space.
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♪
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There's really nothing
more basic to us
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than that cycle of day
and night, that 24-hour cycle.
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All of life on earth evolved
with the day-night cycle,
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so it's ingrained into
every organism on this planet.
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♪
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00:03:01,148 --> 00:03:02,915
Narrator:
Life evolved in lockstep
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with earth's spinning motion.
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♪
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But in the ocean, corals
take things a step further
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♪
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By keeping a record
of every planetary turn.
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♪
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They have a daily cycle,
which creates a deposit
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almost like a tree ring,
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but instead of it being
once a year, it's once a day.
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So, you look a bunch
of tree rings,
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you can count the number
of years the tree was alive.
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♪
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Corals record not just
the yearly cycle,
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but the daily cycle
of night and day.
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These are recorded
in these little growth bands
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in the coral.
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Narrator: By counting
the corals' growth bands,
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we can work out
the number of days in a year.
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Sounds simple, but when we look
at ancient, fossilized coral,
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we discover something strange.
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We can look at fossils of corals
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00:04:01,141 --> 00:04:02,908
that are hundreds of millions
of years old,
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and if we do that, we find that
the year is not 365 days long.
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It's more like 420 days long.
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♪
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Narrator: When the
ancient corals were alive,
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there were 420 days
in one earth year,
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♪
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Meaning a day
was just 21 hours long.
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♪
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To find out how
this was possible,
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we need to go back to the start
of earth's cosmic journey.
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♪
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4.6 billion years ago,
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our planet traveled
a dangerous path
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through a chaotic
and violent solar system.
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♪
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[ Explosion ]
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Collisions were frequent.
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♪
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One giant impact set our planet
spinning rapidly...
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[ Explosion ]
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♪
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♪
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And formed the moon.
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Going all the way back to
the time that the moon formed,
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the earth may have had a day
as short as 2 1/2 hours.
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♪
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Narrator: As the earth
continued on its path
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through the early solar system,
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our planet cooled,
and the surface became solid.
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♪
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But the violence wasn't over.
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The young earth was bombarded
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in the early days
of the solar system,
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00:06:00,327 --> 00:06:02,828
and when these rocks
hit the earth,
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they almost never hit
directly on.
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00:06:04,965 --> 00:06:07,099
They'd hit at an angle.
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♪
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With each collision, it adds
a little bit more momentum
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and a little bit more spin
to the earth.
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00:06:26,286 --> 00:06:29,554
The added spin that you get is
a kind of like a merry-go-round.
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00:06:29,556 --> 00:06:31,990
You can imagine with each kid
that pushes and jumps
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00:06:31,992 --> 00:06:34,760
on the merry-go-round,
you have greater spin.
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00:06:38,132 --> 00:06:41,466
Narrator: As our planet
journeyed on, asteroid impacts
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set the young earth
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00:06:42,903 --> 00:06:46,571
spinning 12 times faster
than it does today.
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Our planet's rotational speed
has huge consequences for life.
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On earth, the spin of our planet
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00:06:56,884 --> 00:07:00,519
actually has an effect
on our weather.
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00:07:00,521 --> 00:07:02,454
With a shorter day,
136
00:07:02,456 --> 00:07:04,990
one of the effects that might
have been apparent on earth
137
00:07:04,992 --> 00:07:08,960
at that time
was more storms developing.
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00:07:08,962 --> 00:07:11,296
[ Thunder crashes ]
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00:07:11,298 --> 00:07:13,765
Narrator: A phenomenon
still in action today
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00:07:13,767 --> 00:07:16,701
drove these powerful
ancient storms.
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00:07:19,306 --> 00:07:22,574
We call it the coriolis effect.
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00:07:22,576 --> 00:07:25,610
The earth's spin
creates phenomena
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00:07:25,612 --> 00:07:27,546
in earth's atmosphere
and oceans.
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00:07:27,548 --> 00:07:29,781
This determines patterns
of circulation
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00:07:29,783 --> 00:07:32,551
in combination with
the heat energy from the sun.
146
00:07:32,553 --> 00:07:35,487
[ Thunder crashes ]
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00:07:35,489 --> 00:07:38,390
The rotation of the earth
matched with solar heating,
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00:07:38,392 --> 00:07:41,460
especially at the equator,
causes air to rise up
149
00:07:41,462 --> 00:07:45,664
and then also sort of to move
sideways and sets up spin.
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00:07:45,666 --> 00:07:48,066
Narrator: As the young earth
continued its journey,
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00:07:48,068 --> 00:07:53,004
the planet's rotation whipped up
ferocious, planet-wide storms.
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The fast spin would have been
disastrous for any life.
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00:08:01,849 --> 00:08:03,248
The storms would have
been so big,
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00:08:03,250 --> 00:08:07,152
it's hard to say if life
would have evolved at all.
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00:08:09,756 --> 00:08:11,790
Narrator: Fortunately
for humankind,
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earth has a
traveling companion --
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the moon, and it helped
slow our planet's spin.
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What happened next was kind of
a wonderful gravitational dance
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between these two bodies.
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As they were spinning,
they were also interacting
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with each other.
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00:08:30,077 --> 00:08:33,345
Narrator: The moon's gravity
pulled on earth's oceans,
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generating tidal bulges.
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Materials moving in and out of
the tidal bulges as they spun,
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and this creates friction
and a kind of drag
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that actually slowed down
the rotation.
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♪
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Narrator: The tides also
helped create life.
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Giant tides swept nutrients
from the land
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into the oceans
for the first time.
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A primordial soup began brewing.
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00:09:02,209 --> 00:09:05,110
♪
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00:09:05,112 --> 00:09:07,279
And life arose.
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00:09:07,281 --> 00:09:14,653
♪
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00:09:14,655 --> 00:09:17,589
As earth's spin continued
to slow down,
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♪
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Life spread across the planet.
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♪
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00:09:28,735 --> 00:09:33,872
But our planet's spin is just
one part of our cosmic ride.
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00:09:33,874 --> 00:09:36,975
Realizing how complicated
our larger environment
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in the universe is
is a wonderful thing.
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There's so many things that
affect the orbit of the earth,
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the tilt of the earth,
things that affect our climate.
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♪
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Narrator: Clues to earth's
space voyage are hidden
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all across the world.
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Could our planet's
wild ride explain
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how one of the driest places
on the planet was once wet?
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♪
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00:10:05,372 --> 00:10:10,575
♪
191
00:10:10,577 --> 00:10:15,780
♪
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00:10:15,782 --> 00:10:21,453
Narrator: The Sahara desert --
dry, dusty, desolate.
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♪
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00:10:23,523 --> 00:10:26,558
But hidden deep in a desert cave
195
00:10:26,560 --> 00:10:30,095
is a clue that
thousands of years ago,
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00:10:30,097 --> 00:10:35,433
the Sahara was a lush,
green paradise.
197
00:10:35,435 --> 00:10:38,737
Archaeologists have
unearthed rock art
198
00:10:38,739 --> 00:10:45,343
which clearly depicts humans
and animals swimming in lakes,
199
00:10:45,345 --> 00:10:47,345
and by looking
at satellite images,
200
00:10:47,347 --> 00:10:51,716
we can trace out the outlines
of ancient river valleys.
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00:10:51,718 --> 00:10:54,619
♪
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00:10:54,621 --> 00:10:56,921
Narrator: The earth's fast
rotation influenced
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00:10:56,923 --> 00:11:00,759
our planet's ancient
weather patterns.
204
00:11:00,761 --> 00:11:05,163
Could another motion
have changed the desert climate?
205
00:11:05,165 --> 00:11:08,199
To unravel the mystery,
we need to rewind the clock
206
00:11:08,201 --> 00:11:10,735
4.6 billion years
207
00:11:10,737 --> 00:11:14,639
♪
208
00:11:14,641 --> 00:11:18,343
To when the infant solar system
209
00:11:18,345 --> 00:11:20,545
was a planetary
shooting gallery
210
00:11:20,547 --> 00:11:27,218
♪
211
00:11:27,220 --> 00:11:32,857
And the earth spun through the
solar system with a slight tilt.
212
00:11:32,859 --> 00:11:34,826
Earlier on, before
the formation of the moon,
213
00:11:34,828 --> 00:11:36,895
the earth didn't have
much of a tilt,
214
00:11:36,897 --> 00:11:39,164
and the impact knocked us
completely out of whack
215
00:11:39,166 --> 00:11:40,999
to about 80 degrees.
216
00:11:41,001 --> 00:11:44,035
[ Explosion ]
217
00:11:47,808 --> 00:11:50,642
Narrator: Our planet might have
continued its journey
218
00:11:50,644 --> 00:11:53,978
tilted right over,
but over billions of years,
219
00:11:53,980 --> 00:11:57,048
the moon's gravity pulled
the earth upright,
220
00:11:57,050 --> 00:11:59,084
just not completely.
221
00:11:59,086 --> 00:12:03,421
The moon is not quite in the
Equatorial plane of the earth.
222
00:12:03,423 --> 00:12:05,356
It's above the Equatorial plane,
223
00:12:05,358 --> 00:12:12,263
and it pulls the earth's axis
into a 23 1/2-degree tilt.
224
00:12:12,265 --> 00:12:14,799
Stricker: If we didn't have
the tilt to about 23 degrees,
225
00:12:14,801 --> 00:12:16,301
then we wouldn't have
the seasons,
226
00:12:16,303 --> 00:12:19,704
and these seasons drive a lot of
the crops and the growth
227
00:12:19,706 --> 00:12:24,409
and the ability to survive
all across the globe.
228
00:12:24,411 --> 00:12:26,945
Narrator: But the ancient
greening of the Sahara
229
00:12:26,947 --> 00:12:31,116
can't be explained
by the changing seasons.
230
00:12:31,118 --> 00:12:35,587
Another planetary motion
must be in play.
231
00:12:35,589 --> 00:12:40,058
A clue is found in the
night sky --
232
00:12:40,060 --> 00:12:43,261
the north star.
233
00:12:43,263 --> 00:12:47,198
Right now, the earth's axis
is pointed towards a star
234
00:12:47,200 --> 00:12:50,368
in the sky called
the north star -- polaris.
235
00:12:50,370 --> 00:12:52,437
We've actually named it
after the fact
236
00:12:52,439 --> 00:12:56,107
that the north pole of the earth
points toward it in the sky.
237
00:12:56,109 --> 00:13:00,712
Narrator: But polaris hasn't
always been the north star.
238
00:13:00,714 --> 00:13:03,081
5,000 years ago,
it was a totally different star.
239
00:13:03,083 --> 00:13:04,883
It was thuban,
which is in Draco,
240
00:13:04,885 --> 00:13:06,417
a different constellation.
241
00:13:06,419 --> 00:13:08,419
Sometime in the future,
it'll be vega,
242
00:13:08,421 --> 00:13:10,755
the brightest star
in the constellation lyra,
243
00:13:10,757 --> 00:13:12,590
so the north star
actually changes
244
00:13:12,592 --> 00:13:16,995
because the north pole's
position in the sky changes.
245
00:13:16,997 --> 00:13:19,597
Narrator: The changing pole star
is evidence
246
00:13:19,599 --> 00:13:23,001
that earth is wobbling
through space.
247
00:13:23,003 --> 00:13:26,171
It's a process called
precession,
248
00:13:26,173 --> 00:13:29,707
something that also affects
spinning tops.
249
00:13:29,709 --> 00:13:32,343
Plait: If you take a top
and let it spin really rapidly
250
00:13:32,345 --> 00:13:33,711
and poke it,
251
00:13:33,713 --> 00:13:36,981
the axis of rotation
will spin around like this,
252
00:13:36,983 --> 00:13:40,118
and it's much slower than
the actual spin of the object.
253
00:13:40,120 --> 00:13:44,823
That is precession, this circle
that the axis is making.
254
00:13:44,825 --> 00:13:46,991
This happens to the earth,
as well.
255
00:13:46,993 --> 00:13:50,595
♪
256
00:13:50,597 --> 00:13:55,066
Narrator: A cosmic poke caused
earth's space wobble,
257
00:13:55,068 --> 00:13:57,602
but what has the power
to poke a planet?
258
00:13:57,604 --> 00:14:00,905
♪
259
00:14:00,907 --> 00:14:04,242
Once again, the key is gravity,
260
00:14:04,244 --> 00:14:07,312
this time earth's
gravitational interactions
261
00:14:07,314 --> 00:14:10,949
with the moon and sun.
262
00:14:10,951 --> 00:14:14,419
These forces are that poke
on the spinning earth,
263
00:14:14,421 --> 00:14:17,722
and that's what makes the
earth's axis spin in precession,
264
00:14:17,724 --> 00:14:22,861
and it takes about 20,000 years
to make a complete circle once.
265
00:14:22,863 --> 00:14:26,130
Narrator: As the earth continues
its journey around the sun,
266
00:14:26,132 --> 00:14:29,934
this precession changes the
planet's climate dramatically.
267
00:14:29,936 --> 00:14:33,271
When the earth's north pole
leans toward the sun,
268
00:14:33,273 --> 00:14:35,907
northern hemisphere
summers are sunnier...
269
00:14:35,909 --> 00:14:40,411
♪
270
00:14:40,413 --> 00:14:44,148
With unexpected consequences
for the Sahara.
271
00:14:44,150 --> 00:14:47,252
♪
272
00:14:47,254 --> 00:14:49,587
Rampino: It turns out
that at times when
273
00:14:49,589 --> 00:14:53,157
the climate in the Sahara
gets more sunshine,
274
00:14:53,159 --> 00:14:55,126
that warms the climate up,
275
00:14:55,128 --> 00:14:57,695
and the winds come in
from the ocean.
276
00:14:57,697 --> 00:15:01,266
It's called the monsoon effect
and brings water --
277
00:15:01,268 --> 00:15:04,702
rain into the Sahara,
where now it's dry.
278
00:15:04,704 --> 00:15:07,305
♪
279
00:15:07,307 --> 00:15:10,575
Olsen: This pattern of
wet and dry climates
280
00:15:10,577 --> 00:15:12,911
that produce this
20,000-year cycle
281
00:15:12,913 --> 00:15:16,948
is what we see in the Sahara,
282
00:15:16,950 --> 00:15:19,117
where at times
of strong monsoon,
283
00:15:19,119 --> 00:15:23,421
the Sahara is wetter,
a green Sahara.
284
00:15:23,423 --> 00:15:25,156
Narrator: 10,000 years ago,
285
00:15:25,158 --> 00:15:27,592
as the earth wobbled
around the sun,
286
00:15:27,594 --> 00:15:32,697
monsoons were unleashed,
turning the desert green.
287
00:15:32,699 --> 00:15:35,767
Humans migrated to the
newly lush Sahara
288
00:15:35,769 --> 00:15:38,803
and created the cave paintings
we see today.
289
00:15:38,805 --> 00:15:40,939
♪
290
00:15:40,941 --> 00:15:45,376
But this wasn't the first time
humans crossed a green Sahara.
291
00:15:45,378 --> 00:15:48,212
♪
292
00:15:48,214 --> 00:15:51,049
Dartnell: A dry Sahara
would have presented
293
00:15:51,051 --> 00:15:53,451
an insurmountable barrier
294
00:15:53,453 --> 00:15:57,155
to our ancestors
for migrating out of Africa,
295
00:15:57,157 --> 00:16:02,260
but during one of these cycles
when the Sahara was green,
296
00:16:02,262 --> 00:16:04,028
it would have been a corridor
297
00:16:04,030 --> 00:16:06,130
that we could have migrated
and dispersed on.
298
00:16:06,132 --> 00:16:08,232
♪
299
00:16:08,234 --> 00:16:10,234
Narrator: As the earth
traveled the cosmos,
300
00:16:10,236 --> 00:16:13,304
our planet's precession
changed the Sahara
301
00:16:13,306 --> 00:16:18,543
and the fate of humankind,
but there are more cosmic forces
302
00:16:18,545 --> 00:16:22,313
affecting our journey
through the universe.
303
00:16:22,315 --> 00:16:24,382
The earth's orbit around the sun
is another thing
304
00:16:24,384 --> 00:16:26,017
that seems very, very solid.
305
00:16:26,019 --> 00:16:29,120
We understand how it works,
but everything in the universe
306
00:16:29,122 --> 00:16:31,723
is a delicately tuned
dance of gravity,
307
00:16:31,725 --> 00:16:36,861
and things can change even
from tiny little influences.
308
00:16:36,863 --> 00:16:39,364
Narrator: As our planet
hurtles through space,
309
00:16:39,366 --> 00:16:43,534
other worlds influence our path.
310
00:16:43,536 --> 00:16:48,339
Could a planetary bully push
earth's climate to the extreme?
311
00:16:48,341 --> 00:16:51,843
[ Ice cracking ]
312
00:16:54,314 --> 00:17:00,985
♪
313
00:17:00,987 --> 00:17:04,856
Narrator: Earth carries us on a
wild journey through the cosmos.
314
00:17:04,858 --> 00:17:07,592
♪
315
00:17:07,594 --> 00:17:09,894
And clues to the effects
of this trip
316
00:17:09,896 --> 00:17:12,030
are hiding in our own backyard.
317
00:17:12,032 --> 00:17:17,168
♪
318
00:17:17,170 --> 00:17:20,171
[ Car horns honking ]
319
00:17:20,173 --> 00:17:22,206
♪
320
00:17:22,208 --> 00:17:27,245
In New York City, amongst the
buildings and traffic,
321
00:17:27,247 --> 00:17:30,281
we find moraines,
322
00:17:30,283 --> 00:17:33,751
rocks left behind
by retreating glaciers.
323
00:17:33,753 --> 00:17:38,389
♪
324
00:17:38,391 --> 00:17:39,957
18,000 years ago,
325
00:17:39,959 --> 00:17:46,097
a sheet of ice taller than any
skyscraper covered Manhattan.
326
00:17:46,099 --> 00:17:50,001
Ice ages have struck regularly
throughout earth's history,
327
00:17:52,172 --> 00:17:55,039
putting our planet
in a deep freeze.
328
00:17:55,041 --> 00:17:58,076
[ Ice cracking ]
329
00:17:58,078 --> 00:17:59,710
Durda: There was a period
in earth's history
330
00:17:59,712 --> 00:18:01,746
several hundred
million years ago,
331
00:18:01,748 --> 00:18:02,980
the snowball earth period,
332
00:18:02,982 --> 00:18:06,017
when we went through
a very extreme glaciation,
333
00:18:06,019 --> 00:18:07,418
if you will,
a very extreme ice age
334
00:18:07,420 --> 00:18:09,687
where we think perhaps
the entire earth
335
00:18:09,689 --> 00:18:11,289
was covered in an ice sheet.
336
00:18:13,259 --> 00:18:15,993
Narrator: The trigger?
337
00:18:15,995 --> 00:18:18,963
Earth's orbital dance
around the sun.
338
00:18:18,965 --> 00:18:21,999
♪
339
00:18:22,001 --> 00:18:23,201
We tend to think of ourselves
340
00:18:23,203 --> 00:18:24,902
sitting relatively stationary
on the earth.
341
00:18:24,904 --> 00:18:26,637
It's pretty comforting,
actually,
342
00:18:26,639 --> 00:18:32,176
but we're orbiting the sun
at about 66,000 miles per hour.
343
00:18:32,178 --> 00:18:36,147
Narrator: Every day, earth
travels over 1.6 million miles
344
00:18:36,149 --> 00:18:40,017
on its journey
around the sun.
345
00:18:40,019 --> 00:18:43,121
This orbit isn't always
completely round.
346
00:18:43,123 --> 00:18:47,091
♪
347
00:18:47,093 --> 00:18:48,826
Earth is generally going
around the sun
348
00:18:48,828 --> 00:18:51,529
in more or less
a circular orbit,
349
00:18:51,531 --> 00:18:56,200
but over time, the massaging
of this orbit from the sun,
350
00:18:56,202 --> 00:18:58,536
from the moon
on the earth's orbit
351
00:18:58,538 --> 00:19:02,006
causes the orbit of the earth
to change
352
00:19:02,008 --> 00:19:03,674
so that sometimes
it's an ellipse.
353
00:19:03,676 --> 00:19:05,476
Sometimes
it's more of a circle.
354
00:19:05,478 --> 00:19:08,146
♪
355
00:19:08,148 --> 00:19:09,580
Right now on the earth,
356
00:19:09,582 --> 00:19:12,150
we're in kind of the most
circular time in the orbit,
357
00:19:12,152 --> 00:19:14,819
so that means the summers
are relatively mild,
358
00:19:14,821 --> 00:19:16,821
and the winters
are relatively mild,
359
00:19:16,823 --> 00:19:19,190
but imagine not that long ago
in the past,
360
00:19:19,192 --> 00:19:22,593
it could have been really
dramatically different.
361
00:19:22,595 --> 00:19:26,164
When the earth is a little bit
closer to the sun,
362
00:19:26,166 --> 00:19:28,466
maybe you have
a really severe summer,
363
00:19:28,468 --> 00:19:29,901
and then on the other side
of the orbit,
364
00:19:29,903 --> 00:19:31,602
you're a little farther away
from the sun than normal,
365
00:19:31,604 --> 00:19:33,671
so you have
a really severe winter.
366
00:19:33,673 --> 00:19:37,108
♪
367
00:19:37,110 --> 00:19:40,878
Our environment is very,
very sensitive to these things,
368
00:19:40,880 --> 00:19:42,914
and when the earth's orbit
is stretched out,
369
00:19:42,916 --> 00:19:45,349
that can actually
trigger an ice age.
370
00:19:45,351 --> 00:19:48,986
♪
371
00:19:48,988 --> 00:19:51,789
Narrator: Our planet's
100,000-year orbital cycle
372
00:19:51,791 --> 00:19:54,592
caused the ice age
that buried New York.
373
00:19:58,798 --> 00:20:04,635
And ice ages have had a big
effect on human history.
374
00:20:04,637 --> 00:20:06,437
15,000 years ago,
375
00:20:06,439 --> 00:20:08,739
plunging temperatures
locked water away
376
00:20:08,741 --> 00:20:11,542
in glaciers and ice caps.
377
00:20:11,544 --> 00:20:17,415
Sea levels dropped, creating
land Bridges between continents.
378
00:20:17,417 --> 00:20:22,420
Humans migrated from Asia
to America by foot,
379
00:20:22,422 --> 00:20:26,157
and for the first time,
America was inhabited.
380
00:20:26,159 --> 00:20:29,527
♪
381
00:20:29,529 --> 00:20:34,498
May 2018 -- scientists revealed
a whole new dynamic
382
00:20:34,500 --> 00:20:36,100
to earth's journey.
383
00:20:36,102 --> 00:20:38,269
♪
384
00:20:38,271 --> 00:20:41,072
Every 405,000 years,
385
00:20:41,074 --> 00:20:45,243
our planet's orbital voyage
stretches to the extreme,
386
00:20:45,245 --> 00:20:50,414
and earth's planetary neighbors
are to blame.
387
00:20:50,416 --> 00:20:52,850
Because Jupiter is the most
massive planet
388
00:20:52,852 --> 00:20:54,218
in our solar system,
389
00:20:54,220 --> 00:20:57,221
it is in many ways the bully
on the playground, right?
390
00:20:57,223 --> 00:21:00,725
Its dynamics, its gravity
sculpts a lot of the dynamics
391
00:21:00,727 --> 00:21:02,326
of the solar system.
392
00:21:02,328 --> 00:21:04,562
♪
393
00:21:04,564 --> 00:21:06,797
Durda: It actually tugs
and pulls on the orbit
394
00:21:06,799 --> 00:21:08,299
of the earth itself.
395
00:21:08,301 --> 00:21:10,501
It's responsible for some of
the very changes
396
00:21:10,503 --> 00:21:13,170
that drive our climatic cycle
here on our planet.
397
00:21:13,172 --> 00:21:16,307
♪
398
00:21:16,309 --> 00:21:19,010
Narrator: Jupiter isn't the only
bully in the playground.
399
00:21:19,012 --> 00:21:20,878
♪
400
00:21:20,880 --> 00:21:22,580
Thaller: Venus is
a fairly big planet
401
00:21:22,582 --> 00:21:24,282
about the size of the earth
402
00:21:24,284 --> 00:21:26,684
and also comes closest
to us in its orbit,
403
00:21:26,686 --> 00:21:30,254
so these two planets put just
a little tiny elongation
404
00:21:30,256 --> 00:21:31,789
onto our earth's orbit,
405
00:21:31,791 --> 00:21:34,458
and as the cycle continues,
the more extreme it gets,
406
00:21:34,460 --> 00:21:36,594
we can actually notice
a temperature difference
407
00:21:36,596 --> 00:21:40,230
that happens about once
every 405,000 years.
408
00:21:40,232 --> 00:21:43,501
♪
409
00:21:43,503 --> 00:21:47,038
Narrator: Jupiter and Venus gang
up on earth gravitationally,
410
00:21:47,040 --> 00:21:52,243
pulling earth's orbit
into an even greater ellipse.
411
00:21:52,245 --> 00:21:54,845
Our planet's hot weather
becomes hotter,
412
00:21:54,847 --> 00:21:58,082
and its cold weather
gets much colder.
413
00:21:58,084 --> 00:22:02,887
♪
414
00:22:02,889 --> 00:22:05,756
Today, we're in a moderate
part of the cycle,
415
00:22:05,758 --> 00:22:08,659
but in just
60,000 years time,
416
00:22:08,661 --> 00:22:14,031
we could plunge
into another deep freeze.
417
00:22:14,033 --> 00:22:16,067
It's a little bit like
a cosmic butterfly effect.
418
00:22:16,069 --> 00:22:18,235
I mean, even
the smallest effects
419
00:22:18,237 --> 00:22:21,539
can have, you know,
a big influence over time.
420
00:22:21,541 --> 00:22:24,542
♪
421
00:22:24,544 --> 00:22:26,110
Narrator:
Earth's orbit around the sun
422
00:22:26,112 --> 00:22:29,680
is just part of our
far larger cosmic journey.
423
00:22:29,682 --> 00:22:32,249
♪
424
00:22:32,251 --> 00:22:35,753
The entire solar system is
hurtling around the milky way,
425
00:22:35,755 --> 00:22:38,856
♪
426
00:22:38,858 --> 00:22:43,227
Taking us places
we don't want to be.
427
00:22:43,229 --> 00:22:45,796
Sometimes our planet
might wander
428
00:22:45,798 --> 00:22:48,466
into what's essentially
a bad neighborhood.
429
00:22:48,468 --> 00:22:50,267
Narrator: What dangers await us?
430
00:22:50,269 --> 00:22:53,671
And could these neighborhoods
spell disaster
431
00:22:53,673 --> 00:22:55,272
for life on earth?
432
00:22:56,809 --> 00:23:03,414
♪
433
00:23:03,416 --> 00:23:09,954
♪
434
00:23:09,956 --> 00:23:14,291
Narrator: Over the last
3.7 billion years,
435
00:23:14,293 --> 00:23:16,961
a series of extinction events
wiped out
436
00:23:16,963 --> 00:23:20,898
almost 95 percent
of all species on earth.
437
00:23:22,568 --> 00:23:24,769
[ Explosion ]
438
00:23:24,771 --> 00:23:28,038
♪
439
00:23:28,040 --> 00:23:30,908
Now research suggests
our planet's orbit
440
00:23:30,910 --> 00:23:33,277
could be partly to blame,
441
00:23:33,279 --> 00:23:36,714
but not the earth's orbit
around the sun,
442
00:23:36,716 --> 00:23:42,253
our planet's larger and longer
journey around the milky way.
443
00:23:42,255 --> 00:23:45,456
Our solar system and our sun
is shooting through the galaxy
444
00:23:45,458 --> 00:23:51,395
at about 530,000 miles per hour
around the center of our galaxy.
445
00:23:51,397 --> 00:23:54,665
And that center of the galaxy is
about 26,000 light-years away,
446
00:23:54,667 --> 00:23:57,735
so it should take the sun
about 230 million years
447
00:23:57,737 --> 00:24:01,038
to trace out one full orbit
around the center of the galaxy.
448
00:24:01,040 --> 00:24:03,574
♪
449
00:24:03,576 --> 00:24:05,609
Narrator: Despite racing
around the milky way
450
00:24:05,611 --> 00:24:08,913
at 1/2 million miles an hour,
451
00:24:08,915 --> 00:24:12,716
earth has completed less than
20 laps of the galaxy
452
00:24:12,718 --> 00:24:16,520
in our planet's entire history,
453
00:24:16,522 --> 00:24:19,990
and it turns out
this galactic ride
454
00:24:19,992 --> 00:24:22,860
is more complicated
than it seems.
455
00:24:22,862 --> 00:24:24,995
Now, if you look at the earth
going around the sun,
456
00:24:24,997 --> 00:24:26,430
it defines an ellipse,
457
00:24:26,432 --> 00:24:28,933
but that's a flat figure,
and you'd think,
458
00:24:28,935 --> 00:24:32,336
"well, the sun probably goes
around in a plane, as well,"
459
00:24:32,338 --> 00:24:34,805
and it turns out
not that simple.
460
00:24:34,807 --> 00:24:37,641
♪
461
00:24:37,643 --> 00:24:39,777
Narrator: Most of the mass
of the solar system
462
00:24:39,779 --> 00:24:42,079
is concentrated in the sun,
463
00:24:42,081 --> 00:24:46,784
so earth and the other planets
smoothly orbit our star.
464
00:24:46,786 --> 00:24:50,187
♪
465
00:24:50,189 --> 00:24:55,359
But the mass of the milky way
is spread out unevenly.
466
00:24:55,361 --> 00:24:57,862
That changes the gravity
of the galaxy,
467
00:24:57,864 --> 00:25:00,831
and so it changes how things
move in it, and in fact,
468
00:25:00,833 --> 00:25:03,934
if you give something a little
bit of an up or down motion,
469
00:25:03,936 --> 00:25:07,371
it'll Bob up and down
as it goes around.
470
00:25:07,373 --> 00:25:10,574
Oluseyi: Riding the earth is
almost like riding a carousel.
471
00:25:10,576 --> 00:25:13,477
As the sun and the earth
go around the galaxy,
472
00:25:13,479 --> 00:25:15,246
the sun also goes up and down
473
00:25:15,248 --> 00:25:17,381
like you're on one of
those horses with the pole,
474
00:25:17,383 --> 00:25:19,049
and so what this can do
475
00:25:19,051 --> 00:25:22,820
is take us into different
galactic environments.
476
00:25:22,822 --> 00:25:26,156
♪
477
00:25:26,158 --> 00:25:29,426
Narrator: This bobbing motion
takes earth and the solar system
478
00:25:29,428 --> 00:25:31,662
on a 60,000-year journey
479
00:25:31,664 --> 00:25:35,432
up and down through
the milky way's galactic plane.
480
00:25:35,434 --> 00:25:37,868
♪
481
00:25:37,870 --> 00:25:39,370
Our orbit also takes us
482
00:25:39,372 --> 00:25:41,872
through different
galactic neighborhoods.
483
00:25:41,874 --> 00:25:45,376
♪
484
00:25:45,378 --> 00:25:50,948
Today, we're traveling through
a calm suburb of the galaxy.
485
00:25:50,950 --> 00:25:55,352
But sometimes things
get a little bumpy.
486
00:25:55,354 --> 00:25:59,089
Sometimes our sun and our planet
might wander
487
00:25:59,091 --> 00:26:01,659
into what's essentially
a bad neighborhood.
488
00:26:01,661 --> 00:26:02,993
You know, maybe it's an area
489
00:26:02,995 --> 00:26:04,962
where there's a lot of
star formation going on,
490
00:26:04,964 --> 00:26:07,898
where there's a lot of young
stars that are very active,
491
00:26:07,900 --> 00:26:11,101
or maybe it's a location
where there are dying stars,
492
00:26:11,103 --> 00:26:14,104
and things are about
to get really hot.
493
00:26:14,106 --> 00:26:16,774
Narrator: The baddest
neighborhoods in the galaxy
494
00:26:16,776 --> 00:26:19,310
may be the spiral arms.
495
00:26:19,312 --> 00:26:21,845
♪
496
00:26:21,847 --> 00:26:25,282
These gas-filled regions orbit
the galactic center
497
00:26:25,284 --> 00:26:28,819
more slowly than the earth,
498
00:26:28,821 --> 00:26:31,989
so our planet
passes through an arm
499
00:26:31,991 --> 00:26:35,559
roughly every 150 million years.
500
00:26:35,561 --> 00:26:39,296
Plait: These arms are where
gas clouds tend to hang out,
501
00:26:39,298 --> 00:26:43,834
and if they get compressed,
they form a lot of stars.
502
00:26:43,836 --> 00:26:48,205
When they form a lot of stars,
they make bright, blue stars.
503
00:26:48,207 --> 00:26:51,642
And they don't last long,
and they blow up as supernovae.
504
00:26:51,644 --> 00:26:56,680
♪
505
00:26:56,682 --> 00:27:00,351
[ Explosion ]
506
00:27:00,353 --> 00:27:03,887
So it's possible that as we're
passing through these regions,
507
00:27:03,889 --> 00:27:06,824
these are places you might not
want to be in,
508
00:27:06,826 --> 00:27:08,225
so in the distant past,
509
00:27:08,227 --> 00:27:10,127
this may have
affected the earth.
510
00:27:10,129 --> 00:27:15,432
♪
511
00:27:15,434 --> 00:27:17,501
Narrator: When giant stars
go supernova,
512
00:27:17,503 --> 00:27:20,237
the stars' outer layers
blast into space
513
00:27:20,239 --> 00:27:23,907
♪
514
00:27:23,909 --> 00:27:25,409
Along with a shock wave
515
00:27:25,411 --> 00:27:28,212
traveling at
20,000 miles a second.
516
00:27:28,214 --> 00:27:31,615
♪
517
00:27:31,617 --> 00:27:37,154
Supernovas also release
cosmic rays --
518
00:27:37,156 --> 00:27:39,890
space bullets
that shoot across the galaxy
519
00:27:39,892 --> 00:27:41,792
at close to the speed of light.
520
00:27:41,794 --> 00:27:44,461
♪
521
00:27:44,463 --> 00:27:46,630
Plait: And you don't want to be
exposed to too many of them,
522
00:27:46,632 --> 00:27:47,998
but in high enough doses,
523
00:27:48,000 --> 00:27:50,634
these things penetrate our cells
and damage our DNA
524
00:27:50,636 --> 00:27:54,538
and over the long-term can cause
really bad damage
525
00:27:54,540 --> 00:27:57,074
to human bodies.
526
00:27:57,076 --> 00:27:58,676
Narrator:
As we ride through space,
527
00:27:58,678 --> 00:28:04,782
earth's magnetic field protects
us from most cosmic rays.
528
00:28:04,784 --> 00:28:08,719
But in 2018,
we discovered evidence
529
00:28:08,721 --> 00:28:10,688
that a hail of space bullets
530
00:28:10,690 --> 00:28:15,559
overwhelmed our planet's
magnetic field in the past.
531
00:28:15,561 --> 00:28:17,561
In many ways,
we really take for granted
532
00:28:17,563 --> 00:28:20,631
how the earth
protects us from space,
533
00:28:20,633 --> 00:28:22,199
but there are records
that we've actually bounced
534
00:28:22,201 --> 00:28:25,869
a little too close
to exploding stars.
535
00:28:25,871 --> 00:28:28,005
Plait: Sediments in the ocean
show that
536
00:28:28,007 --> 00:28:30,107
about 2 million years ago,
537
00:28:30,109 --> 00:28:33,310
iron-60 was deposited
in our oceans.
538
00:28:33,312 --> 00:28:36,046
Iron-60 is a
radioactive isotope of iron,
539
00:28:36,048 --> 00:28:38,749
and there's only way we know of
it being made in the universe,
540
00:28:38,751 --> 00:28:41,351
and that is exploding stars.
541
00:28:41,353 --> 00:28:45,689
♪
542
00:28:45,691 --> 00:28:47,725
Narrator:
Around 2.8 million years ago,
543
00:28:47,727 --> 00:28:52,162
a supernova exploded
just 150 light-years from earth.
544
00:28:54,567 --> 00:28:56,200
A few hundred years later,
545
00:28:56,202 --> 00:29:00,104
a blizzard of cosmic rays
slammed into the earth,
546
00:29:00,106 --> 00:29:02,406
tearing through
our magnetic field.
547
00:29:02,408 --> 00:29:06,443
♪
548
00:29:06,445 --> 00:29:10,481
These space bullets are
prime suspect in the extinction
549
00:29:10,483 --> 00:29:13,450
of over 1/3 of
all coastal marine species.
550
00:29:13,452 --> 00:29:16,120
♪
551
00:29:16,122 --> 00:29:18,422
Plait: Now, this is not
necessarily tied to the earth
552
00:29:18,424 --> 00:29:21,125
passing through one
of these spiral arms,
553
00:29:21,127 --> 00:29:23,861
but it shows you
that being close to a supernova
554
00:29:23,863 --> 00:29:28,098
is not necessarily a thing
you want to do.
555
00:29:28,100 --> 00:29:30,067
Narrator:
Millions of years in the future,
556
00:29:30,069 --> 00:29:33,637
earth will pass through
another spiral arm
557
00:29:33,639 --> 00:29:39,409
as our planet continues its
journey through the milky way.
558
00:29:39,411 --> 00:29:43,781
And we will wander
into harm's way once again.
559
00:29:46,619 --> 00:29:49,019
But there's another part of our
journey through space
560
00:29:49,021 --> 00:29:51,889
that remains a mystery.
561
00:29:51,891 --> 00:29:54,825
The earth is spinning like a top
on its axis.
562
00:29:54,827 --> 00:29:56,260
It's orbiting around the sun.
563
00:29:56,262 --> 00:29:58,662
The sun itself is orbiting
around the center
564
00:29:58,664 --> 00:30:03,500
of the milky way,
but that's far from it.
565
00:30:03,502 --> 00:30:06,170
Narrator: The milky way is
speeding through the universe,
566
00:30:06,172 --> 00:30:11,375
and we are being dragged
along for the ride.
567
00:30:11,377 --> 00:30:14,912
The problem is we can't see
where we're going.
568
00:30:14,914 --> 00:30:18,582
Could earth be headed
for a galactic crash?
569
00:30:18,584 --> 00:30:20,851
♪
570
00:30:22,388 --> 00:30:27,658
♪
571
00:30:27,660 --> 00:30:30,627
[ Screaming ]
572
00:30:30,629 --> 00:30:32,763
♪
573
00:30:32,765 --> 00:30:35,399
Narrator: Like the craziest
of theme park rides,
574
00:30:35,401 --> 00:30:39,703
we are riding the earth on a
wild journey through the cosmos.
575
00:30:39,705 --> 00:30:46,443
♪
576
00:30:46,445 --> 00:30:50,981
Our planet spins, tilts, and
wobbles around the solar system
577
00:30:50,983 --> 00:30:53,116
♪
578
00:30:53,118 --> 00:30:56,720
While bobbing like a carousel
through the milky way.
579
00:30:56,722 --> 00:30:59,223
♪
580
00:30:59,225 --> 00:31:03,026
The dynamics of the earth
moving in the cosmic void is,
581
00:31:03,028 --> 00:31:06,697
like, the most unbelievable
journey you could ever imagine,
582
00:31:06,699 --> 00:31:08,699
and as you get to larger scales,
583
00:31:08,701 --> 00:31:12,169
the motions only become grander
and larger and more dynamic.
584
00:31:12,171 --> 00:31:16,039
♪
585
00:31:16,041 --> 00:31:19,176
Narrator: In 1977,
we tried to work out
586
00:31:19,178 --> 00:31:21,078
the largest motion of all --
587
00:31:21,080 --> 00:31:23,647
♪
588
00:31:23,649 --> 00:31:27,851
The movement of our galaxy
through the universe.
589
00:31:27,853 --> 00:31:31,154
Clues hide in the
cosmic microwave background,
590
00:31:31,156 --> 00:31:34,524
a remnant from the birth
of the universe.
591
00:31:34,526 --> 00:31:37,094
Bullock: The cosmic microwave
background is the radiation
592
00:31:37,096 --> 00:31:40,397
that's left over
from the hot big bang.
593
00:31:40,399 --> 00:31:43,166
The cosmic microwave background
is shining in all directions
594
00:31:43,168 --> 00:31:44,902
as sort of this fixed thing,
595
00:31:44,904 --> 00:31:47,337
and if we're moving through it
with some speed,
596
00:31:47,339 --> 00:31:49,373
we will see that
in the light itself.
597
00:31:49,375 --> 00:31:51,275
You can measure that,
and by measuring that,
598
00:31:51,277 --> 00:31:55,946
you can get a sense of how fast
we're moving through that space.
599
00:31:55,948 --> 00:31:58,115
Narrator: By tracking our
movement through the universe
600
00:31:58,117 --> 00:31:59,716
against a fixed point,
601
00:31:59,718 --> 00:32:03,553
we can work out the milky way's
speed and direction.
602
00:32:03,555 --> 00:32:06,390
♪
603
00:32:06,392 --> 00:32:13,030
But in 1977, telescopes weren't
the best tool for the job.
604
00:32:13,032 --> 00:32:15,565
Tremblay:
During the cold war, 1977,
605
00:32:15,567 --> 00:32:18,201
you have the newly declassified
u-2 spy plane,
606
00:32:18,203 --> 00:32:21,238
this very high-altitude
reconnaissance aircraft.
607
00:32:21,240 --> 00:32:24,775
NASA retrofitted one of them
with an upward-facing window,
608
00:32:24,777 --> 00:32:26,710
and with very
sensitive receivers,
609
00:32:26,712 --> 00:32:29,379
this spy plane became
the first experiment
610
00:32:29,381 --> 00:32:32,849
to for the first time
definitively measure the motion
611
00:32:32,851 --> 00:32:35,018
of the galaxy
through the universe.
612
00:32:35,020 --> 00:32:38,121
Narrator: As the u-2 spy plane
soared above the earth,
613
00:32:38,123 --> 00:32:41,024
it measured the
cosmic microwave background
614
00:32:41,026 --> 00:32:42,893
in unprecedented detail.
615
00:32:42,895 --> 00:32:46,096
♪
616
00:32:46,098 --> 00:32:49,366
The data revealed
that our galaxy races
617
00:32:49,368 --> 00:32:53,537
through the universe
at 370 miles a second.
618
00:32:53,539 --> 00:32:57,374
♪
619
00:32:57,376 --> 00:32:59,476
That's over 1 million miles
an hour.
620
00:32:59,478 --> 00:33:03,347
♪
621
00:33:03,349 --> 00:33:05,949
Sutter: Think of how big
a galaxy is.
622
00:33:05,951 --> 00:33:08,819
Hundreds of millions of stars,
623
00:33:08,821 --> 00:33:12,622
and we're moving at
hundreds of miles per second.
624
00:33:12,624 --> 00:33:14,725
That's just a tiny bit
mind-blowing.
625
00:33:14,727 --> 00:33:16,860
♪
626
00:33:16,862 --> 00:33:20,130
Narrator: The milky way's speed
isn't the most alarming part
627
00:33:20,132 --> 00:33:22,766
of our galactic journey.
628
00:33:22,768 --> 00:33:26,703
From earth, we can't even see
in the direction our galaxy
629
00:33:26,705 --> 00:33:28,071
is taking us.
630
00:33:28,073 --> 00:33:29,639
We're flying blind.
631
00:33:29,641 --> 00:33:33,110
Our view is blocked
by the milky way itself.
632
00:33:33,112 --> 00:33:36,079
♪
633
00:33:36,081 --> 00:33:38,682
So if you're actually looking
through the plane of the galaxy,
634
00:33:38,684 --> 00:33:40,584
through the plane
of the pancake,
635
00:33:40,586 --> 00:33:43,220
your view of the galaxy
is obscured
636
00:33:43,222 --> 00:33:47,924
by curtains of dust and gas
that envelop our solar system.
637
00:33:47,926 --> 00:33:49,726
Bullock: It's very bright.
There's a lot of stars.
638
00:33:49,728 --> 00:33:53,130
And our view is blocked
by the galaxy itself,
639
00:33:53,132 --> 00:33:56,166
so there's a zone
directly behind the galaxy
640
00:33:56,168 --> 00:33:58,402
as we look towards
the galactic center
641
00:33:58,404 --> 00:34:00,270
that's really an unknown area.
642
00:34:00,272 --> 00:34:02,305
It's a zone we call
the zone of avoidance,
643
00:34:02,307 --> 00:34:05,075
and it's an area of really
cosmic mystery.
644
00:34:05,077 --> 00:34:07,310
♪
645
00:34:07,312 --> 00:34:11,081
Narrator: Thanks to this
mysterious zone,
646
00:34:11,083 --> 00:34:14,851
we thought we could be headed
for a galactic car crash.
647
00:34:14,853 --> 00:34:20,323
♪
648
00:34:20,325 --> 00:34:22,459
Then we had a breakthrough.
649
00:34:22,461 --> 00:34:28,665
♪
650
00:34:28,667 --> 00:34:31,268
We used powerful
radio telescopes
651
00:34:31,270 --> 00:34:33,570
to look through
the zone of avoidance
652
00:34:33,572 --> 00:34:35,072
for the first time.
653
00:34:35,074 --> 00:34:41,678
♪
654
00:34:41,680 --> 00:34:44,247
Bullock: One of the nice things
about using light that's
655
00:34:44,249 --> 00:34:47,784
in the radio is that this kind
of light actually can go through
656
00:34:47,786 --> 00:34:50,353
pretty dense kinds
of gas and stars
657
00:34:50,355 --> 00:34:53,757
and allows us
to sort of look through things.
658
00:34:53,759 --> 00:34:55,926
Using these radio telescopes
has given us a glimpse
659
00:34:55,928 --> 00:35:00,530
into what lies beyond
the zone of avoidance.
660
00:35:00,532 --> 00:35:03,366
Narrator: Peering through
the zone of avoidance,
661
00:35:03,368 --> 00:35:07,070
we found that the milky way's
path is clear,
662
00:35:07,072 --> 00:35:08,872
but that's not all.
663
00:35:08,874 --> 00:35:12,442
We also discovered we are just
one tiny part
664
00:35:12,444 --> 00:35:14,978
of a vast cluster of galaxies
665
00:35:14,980 --> 00:35:18,081
sailing through
the cosmos together.
666
00:35:18,083 --> 00:35:20,383
We think that our galaxy,
the milky way,
667
00:35:20,385 --> 00:35:24,354
is part of a much grander
cosmic flow of galaxies,
668
00:35:24,356 --> 00:35:26,056
and it is part of what might be
669
00:35:26,058 --> 00:35:28,391
the laniakea supercluster
of galaxies,
670
00:35:28,393 --> 00:35:30,861
this giant, giant
cosmic structure
671
00:35:30,863 --> 00:35:33,463
filled with potentially
thousands of galaxies
672
00:35:33,465 --> 00:35:35,565
that is moving together
in this beautiful,
673
00:35:35,567 --> 00:35:37,400
like, slow-moving river
674
00:35:37,402 --> 00:35:40,437
that is sculpted and dictated
by gravity itself.
675
00:35:40,439 --> 00:35:43,206
♪
676
00:35:43,208 --> 00:35:47,043
Narrator: Earth voyages through
space along gravitational rivers
677
00:35:47,045 --> 00:35:50,680
hundreds of millions
of light-years long
678
00:35:50,682 --> 00:35:54,618
along with a fleet
of 100,000 other galaxies,
679
00:35:54,620 --> 00:35:58,622
all moving toward
a single point in space,
680
00:35:58,624 --> 00:36:04,728
a gravitational drain
known as the great attractor.
681
00:36:04,730 --> 00:36:10,500
Sutter: The great attractor is
the local region of gravity,
682
00:36:10,502 --> 00:36:13,670
of strong gravity
in this patch of the universe.
683
00:36:13,672 --> 00:36:16,973
It's where all the galaxies
in this chunk of the universe
684
00:36:16,975 --> 00:36:20,043
are flowing towards.
685
00:36:20,045 --> 00:36:22,812
At the location of the
great attractor
686
00:36:22,814 --> 00:36:23,980
is a bunch of material --
687
00:36:23,982 --> 00:36:25,882
a bunch of gas,
a bunch of galaxies,
688
00:36:25,884 --> 00:36:29,085
an extremely massive cluster,
689
00:36:29,087 --> 00:36:33,290
and over time,
more and more galaxies
690
00:36:33,292 --> 00:36:35,659
add themselves to this cluster
691
00:36:35,661 --> 00:36:40,230
as they continue to join
the great attractor.
692
00:36:40,232 --> 00:36:42,933
Narrator: It's unlikely earth
will ever reach
693
00:36:42,935 --> 00:36:45,669
the great attractor.
694
00:36:45,671 --> 00:36:52,442
It seems the milky way is headed
for a collision after all.
695
00:36:52,444 --> 00:36:55,579
Is this how our
cosmic journey ends?
696
00:36:55,581 --> 00:36:57,280
♪
697
00:36:58,650 --> 00:37:06,890
♪
698
00:37:06,892 --> 00:37:08,959
Narrator: Earth's voyage
across the cosmos
699
00:37:08,961 --> 00:37:12,762
has lasted
for 4.5 billion years.
700
00:37:12,764 --> 00:37:17,634
♪
701
00:37:17,636 --> 00:37:21,938
The big question -- how will our
journey finally end?
702
00:37:21,940 --> 00:37:25,008
♪
703
00:37:25,010 --> 00:37:27,043
A clue comes from
the milky way's
704
00:37:27,045 --> 00:37:31,114
traveling companion --
another galaxy, Andromeda,
705
00:37:31,116 --> 00:37:34,584
♪
706
00:37:34,586 --> 00:37:37,320
Filled with up
to a trillion stars
707
00:37:37,322 --> 00:37:40,090
that's charting
a similar path to us.
708
00:37:40,092 --> 00:37:44,995
♪
709
00:37:44,997 --> 00:37:47,897
The Andromeda galaxy is another
big spiral galaxy,
710
00:37:47,899 --> 00:37:49,532
a lot like our milky way,
711
00:37:49,534 --> 00:37:54,604
and it turns out the two of us
are heading for each other.
712
00:37:54,606 --> 00:37:56,640
Narrator: Andromeda
and the milky way
713
00:37:56,642 --> 00:38:00,677
are currently 2.5 million
light-years apart,
714
00:38:00,679 --> 00:38:03,280
but they're hurtling
towards each other
715
00:38:03,282 --> 00:38:06,016
at over 250,000 miles an hour.
716
00:38:06,018 --> 00:38:08,818
♪
717
00:38:08,820 --> 00:38:12,255
A collision is inevitable.
718
00:38:12,257 --> 00:38:13,923
Stricker: Galaxies colliding
with each other
719
00:38:13,925 --> 00:38:15,759
sounds like science fiction,
720
00:38:15,761 --> 00:38:17,861
but the collision of
the Andromeda galaxy
721
00:38:17,863 --> 00:38:22,565
and the milky way galaxy
will be a spectacular event.
722
00:38:22,567 --> 00:38:25,101
Oluseyi: When the Andromeda and
milky way galaxies collide,
723
00:38:25,103 --> 00:38:28,872
it's gonna be
a ridiculous light show.
724
00:38:28,874 --> 00:38:32,876
The stars don't collide,
but the giant clouds of gas do,
725
00:38:32,878 --> 00:38:35,111
and that's gonna trigger
star formation,
726
00:38:35,113 --> 00:38:38,381
so we're gonna have what's
known as a starburst galaxy.
727
00:38:38,383 --> 00:38:40,517
♪
728
00:38:40,519 --> 00:38:43,453
When Andromeda finally merges
with the milky way,
729
00:38:43,455 --> 00:38:45,488
all bets are off.
730
00:38:45,490 --> 00:38:48,525
All of a sudden, a system
of hundreds of billions of stars
731
00:38:48,527 --> 00:38:52,362
will be added to our own,
and there will be mass chaos,
732
00:38:52,364 --> 00:38:54,130
but one thing
you can guarantee --
733
00:38:54,132 --> 00:38:56,633
there is going to be
celestial fireworks.
734
00:38:56,635 --> 00:38:59,869
♪
735
00:38:59,871 --> 00:39:02,939
Narrator: This could be the
biggest light show in history,
736
00:39:02,941 --> 00:39:07,911
resulting in the creation
of a brand-new galaxy.
737
00:39:07,913 --> 00:39:11,214
We will have become
one giant galaxy.
738
00:39:11,216 --> 00:39:13,483
Call it milkdromeda,
if you will,
739
00:39:13,485 --> 00:39:15,251
so we will look very different.
740
00:39:15,253 --> 00:39:18,822
Our grand-design, spiral
milky way galaxy
741
00:39:18,824 --> 00:39:21,891
will have probably
transformed itself
742
00:39:21,893 --> 00:39:26,296
into an entirely
different shape.
743
00:39:26,298 --> 00:39:28,531
Narrator: The merging galaxies
could create
744
00:39:28,533 --> 00:39:31,668
a giant,
elliptical-shaped galaxy,
745
00:39:31,670 --> 00:39:35,271
but earth might not
be around to see it.
746
00:39:35,273 --> 00:39:38,742
Billions of stars are gonna
come careening into our galaxy,
747
00:39:38,744 --> 00:39:43,012
very, very easily disrupting
the orbit of the earth.
748
00:39:43,014 --> 00:39:46,049
The sun could be thrown
out of the galaxy entirely.
749
00:39:46,051 --> 00:39:49,819
♪
750
00:39:49,821 --> 00:39:53,289
Narrator: As stars, dust, and
gas swirl around each other,
751
00:39:53,291 --> 00:39:55,959
♪
752
00:39:55,961 --> 00:40:00,096
Gravitational interactions
could slingshot our solar system
753
00:40:00,098 --> 00:40:02,799
out into intergalactic space.
754
00:40:02,801 --> 00:40:08,204
♪
755
00:40:08,206 --> 00:40:10,206
We'll still orbit the sun,
and everything will be fine,
756
00:40:10,208 --> 00:40:11,841
kind of, but it just means
757
00:40:11,843 --> 00:40:14,110
we'll see something
very different in our sky
758
00:40:14,112 --> 00:40:19,215
in 4.6 billion years
than we do now.
759
00:40:19,217 --> 00:40:20,683
Narrator:
Our planet could be sent
760
00:40:20,685 --> 00:40:23,686
on a whole new
intergalactic ride,
761
00:40:23,688 --> 00:40:25,722
♪
762
00:40:25,724 --> 00:40:32,695
Shot out into the cosmos, away
from the new milkdromeda galaxy.
763
00:40:32,697 --> 00:40:35,098
There's no way of knowing
exactly what's going to happen,
764
00:40:35,100 --> 00:40:38,101
and in that sense,
journey's end...
765
00:40:38,103 --> 00:40:42,272
♪
766
00:40:42,274 --> 00:40:43,873
We'll just have to wait and see.
767
00:40:43,875 --> 00:40:51,414
♪
768
00:40:51,416 --> 00:40:53,850
Narrator: We might not know
the final destination
769
00:40:53,852 --> 00:40:57,887
for earth's cosmic journey,
but we do know this --
770
00:40:57,889 --> 00:41:02,425
so far, it has been
an incredible ride.
771
00:41:02,427 --> 00:41:04,594
We've had a fantastic journey
772
00:41:04,596 --> 00:41:07,897
over the history
of earth's existence.
773
00:41:07,899 --> 00:41:11,234
We may not be immediately aware
of our motions
774
00:41:11,236 --> 00:41:14,437
through the universe, but that
doesn't mean they're not there.
775
00:41:14,439 --> 00:41:16,806
♪
776
00:41:16,808 --> 00:41:18,508
Many people think of the earth
777
00:41:18,510 --> 00:41:23,079
as this blue, calm marble
in space.
778
00:41:23,081 --> 00:41:26,216
But in reality, it's violently
ripping around the sun,
779
00:41:26,218 --> 00:41:28,952
and the sun is ripping
about the galaxy.
780
00:41:28,954 --> 00:41:31,254
♪
781
00:41:31,256 --> 00:41:33,456
There's a lot of dynamics
happening.
782
00:41:33,458 --> 00:41:35,525
♪
783
00:41:35,527 --> 00:41:37,293
It boggles the mind
just to think
784
00:41:37,295 --> 00:41:41,664
of what the earth
will have done.
785
00:41:41,666 --> 00:41:44,767
The earth will have
actually orbited the sun
786
00:41:44,769 --> 00:41:46,202
10 billion times.
787
00:41:46,204 --> 00:41:49,606
It will have spun on its axis,
like, a trillion times
788
00:41:49,608 --> 00:41:52,408
in a galaxy
that's moving through space.
789
00:41:52,410 --> 00:41:55,545
[ Exhales ]
790
00:41:55,547 --> 00:41:58,781
Riding the earth is anything
but a boring trip.
791
00:41:58,783 --> 00:42:03,520
♪
792
00:42:03,570 --> 00:42:08,120
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