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[pensive music playing]
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[birds squawking]
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[Freeman] The far north of our planet
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00:00:30,640 --> 00:00:32,800
is a land of extremes.
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[pensive music continues]
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When winter takes hold…
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[wind gusting]
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…arctic winds cause temperatures
to plummet.
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Even the hardy Alaskan brown bear
must take refuge.
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[bear grunts]
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[Freeman] Unable to endure
the freezing conditions,
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they are forced
to embark on an extraordinary journey.
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[pensive music continues]
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As the North Pole tilts
into the darkness and cold of winter…
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the bears begin climbing
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high into the mountains…
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to find shelter in caves or dens
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dug into the steep slopes.
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Hundreds of meters up.
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[ominous music playing]
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[snow crumbling]
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[wind gusting]
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[ominous music continues]
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Bears living at the ends of the Earth
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must contend with the incredible
challenges each season brings.
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[suspenseful music playing]
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To do it,
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they rely on a very special connection
to the universe,
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because written into a bear's biology
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is every critical moment…
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[whooshing]
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…of Earth's
four-and-a-half-billion-year history.
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Events of unimaginable power…
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[rumbling]
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…and destruction
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that have created a world
like nowhere else in our universe.
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[dramatic music playing]
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[ethereal music playing]
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[bear grunting]
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[sniffing]
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[Freeman] This is Luna,
a six-year-old female.
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Having reached the safety of her den…
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this will be her home
for the next six months.
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[Luna huffs]
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A cozy spot
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to see out the winter in hibernation.
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[Luna breathing heavily]
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[grunts]
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As the days get shorter…
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her body responds
to the rhythm of our planet.
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[whooshing]
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[heartbeat thumping]
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Her heart rate begins to slow…
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[heartbeat slows slightly]
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…to just eight beats per minute.
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[heartbeat slows dramatically]
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[Luna huffs]
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As she settles down…
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her body temperature drops.
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[heartbeat continues slowly]
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[ethereal music playing]
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And she falls into a deep, dreamful sleep.
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[Luna snoring]
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[ethereal music continues]
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The powerful connection
between bear and universe…
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compels her to spend
the harsh winter months underground.
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[pensive music playing]
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Blissfully unaware
of the long journey ahead.
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Because outside the den…
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[whooshing]
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…Earth is on the move.
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[pensive music continues]
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Every day,
the planet spins once on its axis.
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[whooshing]
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[pensive music continues]
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Each month, the Moon completes
one full circuit around the Earth.
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00:07:07,040 --> 00:07:08,680
And as the months pass,
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the Earth and the Moon orbit the Sun.
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[whooshing]
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During the time she'll spend asleep,
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Luna will travel 470 million kilometers.
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[pensive music continues]
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An epic cosmic voyage
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halfway around the Sun.
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[calm music playing]
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And this year,
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she has some new traveling companions.
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[cub moaning]
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While in and out of sleep…
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[cub yowls]
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…Luna has given birth…
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00:08:04,040 --> 00:08:05,880
to two little bears.
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The cubs will eat and sleep
in the den until springtime.
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But two more mouths to feed
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is taking its toll on Luna's body.
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[whooshing]
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Fat cells beneath her skin begin to shrink
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as her energy stores
are used up producing milk.
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[pensive music playing]
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After five months underground,
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Luna has already lost
more than a quarter of her body weight.
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[cubs grunting softly]
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[wind howling]
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00:09:01,120 --> 00:09:04,440
And with outside temperatures
still locked below zero…
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Luna urgently needs spring to arrive
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if she is to continue feeding
her newborn cubs.
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[cub snoring]
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Luckily,
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Earth has a happy quirk.
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It's tilted on its side.
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[calm music playing]
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And so, as it moves through space,
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at different times of the year,
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different parts
of the planet lean toward the Sun,
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causing the seasons to turn.
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Which means, in Alaska,
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something remarkable is happening.
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[ethereal music playing]
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With each passing day,
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00:10:14,840 --> 00:10:17,000
the Sun gets higher in the sky.
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00:10:20,840 --> 00:10:23,680
Its warming rays transforming
the landscape.
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Just when Luna and her cubs need it most.
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Nerve endings in her skin detect
the warmth of the Sun.
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[majestic music playing]
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And as the days get longer…
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[Luna snorting]
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[whooshing]
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00:11:01,120 --> 00:11:04,000
…specialized cells in the back of her eye
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00:11:05,480 --> 00:11:09,000
sense the tiny increases in light levels.
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[majestic music continues]
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00:11:14,680 --> 00:11:16,960
These secret messages,
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00:11:17,040 --> 00:11:19,200
direct from our nearest star…
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00:11:22,400 --> 00:11:26,280
tell Luna it's time
to wake from hibernation.
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00:11:27,920 --> 00:11:29,160
[Luna groans loudly]
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00:11:35,720 --> 00:11:37,320
[yawning]
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00:11:40,720 --> 00:11:45,160
As they signal the gentle turning
of our planet's seasons.
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[snorts]
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[groans, snorts]
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[whooshing]
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00:11:54,320 --> 00:11:56,000
But out in the solar system…
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00:11:58,200 --> 00:12:00,040
seasons like Earth's
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00:12:01,880 --> 00:12:03,200
are far from typical.
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[ominous music playing]
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00:12:09,640 --> 00:12:12,160
Our nearest neighbor, Venus…
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00:12:12,680 --> 00:12:13,800
[whooshing]
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00:12:14,920 --> 00:12:16,680
…is much closer to the Sun
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00:12:17,640 --> 00:12:20,360
and so is much hotter than Earth.
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[whooshing]
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[fizzling]
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00:12:25,160 --> 00:12:28,120
And because the planet has no tilt,
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it has virtually no seasons.
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[ominous music continues]
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00:12:35,480 --> 00:12:39,400
Temperatures remain searingly hot
all year round.
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00:12:44,280 --> 00:12:45,560
Further away,
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00:12:46,080 --> 00:12:47,480
out past Earth…
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00:12:47,560 --> 00:12:48,840
[whooshing]
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…is Mars,
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whose orbit causes its distance
from the Sun
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00:12:56,200 --> 00:12:58,440
to vary dramatically through the year,
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00:13:00,160 --> 00:13:01,960
making seasons on Mars…
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[ice crackling]
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00:13:03,600 --> 00:13:06,440
…far more extreme than our own.
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00:13:09,200 --> 00:13:13,880
During winter, over a quarter
of the planet's atmosphere freezes solid.
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00:13:15,880 --> 00:13:17,040
While in summer,
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00:13:18,120 --> 00:13:20,440
when Mars passes closer to the Sun,
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00:13:21,240 --> 00:13:24,280
the increased heat creates dust storms
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00:13:24,360 --> 00:13:29,280
so severe
they can engulf the entire planet.
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00:13:29,360 --> 00:13:31,160
[suspenseful music playing]
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00:13:31,240 --> 00:13:33,280
[whooshing]
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00:13:33,360 --> 00:13:34,800
But beyond Mars,
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00:13:36,480 --> 00:13:37,680
past Jupiter…
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00:13:37,760 --> 00:13:39,600
[whooshing]
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00:13:41,080 --> 00:13:42,000
…and Saturn…
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00:13:44,800 --> 00:13:46,520
[whooshing]
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00:13:48,080 --> 00:13:51,000
…three billion kilometers from the Sun,
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00:13:52,600 --> 00:13:57,200
Uranus has the most extreme seasons
in the solar system.
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This planet spins on its side.
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00:14:04,280 --> 00:14:06,240
So as it orbits,
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00:14:06,320 --> 00:14:08,480
the summer side faces the Sun…
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00:14:09,000 --> 00:14:11,280
[wind gusting]
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00:14:12,040 --> 00:14:17,080
…while the winter side
won't see daylight for 42 years.
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00:14:21,280 --> 00:14:24,520
[whooshing]
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00:14:24,600 --> 00:14:27,080
[ethereal music playing]
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00:14:29,400 --> 00:14:32,800
Only Earth has seasons
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00:14:34,440 --> 00:14:37,440
that, even at the extremes of our planet,
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00:14:38,200 --> 00:14:40,440
allow life a fighting chance.
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00:14:47,000 --> 00:14:49,400
[calm music playing]
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00:14:54,520 --> 00:14:56,120
With the arrival of spring,
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00:14:57,280 --> 00:14:59,600
Luna's family emerge from the den.
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00:15:01,280 --> 00:15:03,800
[cubs grunting softly]
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00:15:06,280 --> 00:15:11,000
The cubs can now enjoy
their first moments in the Sun.
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00:15:13,880 --> 00:15:15,320
[cubs continue grunting]
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00:15:19,880 --> 00:15:20,880
[cub yowls]
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00:15:20,960 --> 00:15:23,160
[calm music continues]
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00:15:35,880 --> 00:15:40,360
But the turning seasons mean the cubs
must now set off on a daunting journey.
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00:15:48,280 --> 00:15:49,760
Because to find food,
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00:15:50,840 --> 00:15:53,480
Luna must lead them back to the lowlands
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00:15:54,760 --> 00:15:56,760
on the other side of the mountain.
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00:16:01,960 --> 00:16:04,360
[pensive music playing]
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00:16:04,440 --> 00:16:05,440
[Luna grunts]
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00:16:13,720 --> 00:16:16,000
It's a grueling climb for little legs.
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00:16:16,760 --> 00:16:19,120
[majestic music playing]
203
00:16:23,840 --> 00:16:27,320
With hundreds of meters
of ice and rock to overcome.
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00:16:27,400 --> 00:16:29,200
[intriguing music playing]
205
00:16:29,280 --> 00:16:30,440
[cubs grunting]
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00:16:50,560 --> 00:16:53,200
[calm music playing]
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00:17:01,440 --> 00:17:02,320
[Luna groaning]
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00:17:13,080 --> 00:17:14,000
[cub whines]
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00:17:21,040 --> 00:17:25,280
Once they're over the summit,
the hardest part of the trek is over.
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00:17:25,360 --> 00:17:27,720
[calm music continues]
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00:17:28,840 --> 00:17:30,000
[Luna groans]
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00:17:36,760 --> 00:17:39,920
But survival is far from guaranteed.
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00:17:43,560 --> 00:17:45,920
To make it through the rest of the year,
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00:17:47,240 --> 00:17:48,840
the family will rely…
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00:17:48,920 --> 00:17:49,920
[whooshing]
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00:17:50,000 --> 00:17:52,000
…on Luna's instinctive understanding
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00:17:53,200 --> 00:17:54,640
of the seasons ahead.
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00:17:54,720 --> 00:17:57,320
[ethereal music playing]
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00:17:58,920 --> 00:18:00,280
Each one…
220
00:18:02,640 --> 00:18:05,480
a result of Earth's yearly journey
through space.
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00:18:12,440 --> 00:18:13,840
A journey that began…
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00:18:14,480 --> 00:18:15,840
[whooshing]
223
00:18:15,920 --> 00:18:18,960
…before the Earth even existed.
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00:18:23,280 --> 00:18:26,080
[ethereal music playing]
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00:18:33,640 --> 00:18:39,600
A time when our solar system
was little more than ash.
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00:18:43,120 --> 00:18:44,120
No Sun,
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00:18:44,880 --> 00:18:45,720
no planets,
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00:18:46,440 --> 00:18:47,600
and no moons.
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00:18:50,360 --> 00:18:53,920
Just a vast cloud of gas and dust.
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00:18:54,000 --> 00:18:56,400
[mysterious music playing]
231
00:19:07,320 --> 00:19:10,960
Then, in a distant solar system…
232
00:19:11,040 --> 00:19:13,320
[ominous music playing]
233
00:19:13,400 --> 00:19:14,920
…a star explodes.
234
00:19:15,000 --> 00:19:16,840
[rumbling in distance]
235
00:19:16,920 --> 00:19:21,800
A supernova that sends
a shock wave across the galaxy.
236
00:19:21,880 --> 00:19:24,080
[dramatic music playing]
237
00:19:27,560 --> 00:19:29,960
[rumbling growing louder]
238
00:19:34,200 --> 00:19:35,960
[dramatic music crescendos]
239
00:19:41,280 --> 00:19:46,280
On impact, the shockwave
causes the cloud to fall in on itself.
240
00:19:46,360 --> 00:19:48,880
[ethereal music playing]
241
00:19:51,680 --> 00:19:53,440
And begin to rotate.
242
00:19:53,520 --> 00:19:55,880
[whooshing]
243
00:20:00,440 --> 00:20:02,640
As it spins faster and faster,
244
00:20:04,040 --> 00:20:08,280
the cloud flattens out into a disc.
245
00:20:10,200 --> 00:20:13,200
A maelstrom of gas and rock.
246
00:20:16,600 --> 00:20:19,400
In the center, under intense pressure…
247
00:20:21,880 --> 00:20:22,960
[crashing]
248
00:20:23,040 --> 00:20:24,480
…the Sun is born.
249
00:20:28,080 --> 00:20:31,840
While further out,
rock collides with rock…
250
00:20:34,080 --> 00:20:36,200
and our planet begins to grow.
251
00:20:41,080 --> 00:20:43,480
Until after 20 million years,
252
00:20:44,880 --> 00:20:46,760
Earth is fully formed.
253
00:20:49,360 --> 00:20:52,720
Still circling the Sun like the cloud
from which it grew.
254
00:20:52,800 --> 00:20:55,560
[dramatic music playing]
255
00:20:58,920 --> 00:21:02,280
Orbiting once every 365 days,
256
00:21:05,520 --> 00:21:07,440
which is how Earth got its year.
257
00:21:14,240 --> 00:21:16,600
But at this point in the planet's story,
258
00:21:17,760 --> 00:21:19,520
it's a year without seasons.
259
00:21:20,920 --> 00:21:21,800
[whooshing]
260
00:21:21,880 --> 00:21:24,000
[rumbling]
261
00:21:24,080 --> 00:21:26,720
Because the chaos that created them…
262
00:21:29,200 --> 00:21:31,080
is still to come.
263
00:21:32,200 --> 00:21:35,560
[insects, birds chirping]
264
00:21:38,600 --> 00:21:41,480
[calm music playing]
265
00:21:41,560 --> 00:21:42,680
In Alaska,
266
00:21:43,640 --> 00:21:45,360
the vibrancy of spring…
267
00:21:45,440 --> 00:21:46,520
[cub whining]
268
00:21:46,600 --> 00:21:49,280
…has given way to lazy summer days.
269
00:22:01,480 --> 00:22:03,880
The cubs are now five months old.
270
00:22:03,960 --> 00:22:05,040
[cub whining]
271
00:22:05,120 --> 00:22:06,520
[playful music playing]
272
00:22:06,600 --> 00:22:08,120
And still learning…
273
00:22:10,400 --> 00:22:11,560
how to be bears.
274
00:22:12,200 --> 00:22:13,080
[cub yelping]
275
00:22:25,000 --> 00:22:27,080
Because they're growing so quickly,
276
00:22:28,040 --> 00:22:29,960
the cubs are constantly hungry.
277
00:22:36,520 --> 00:22:38,800
And while it might look idyllic…
278
00:22:41,040 --> 00:22:44,480
summer in Alaska is a time of hardship.
279
00:22:44,560 --> 00:22:47,560
[pensive music playing]
280
00:22:51,360 --> 00:22:53,200
[sniffs]
281
00:22:53,280 --> 00:22:54,160
[whines]
282
00:22:54,680 --> 00:22:57,520
Without a decent meal to be found
in the meadows,
283
00:22:58,040 --> 00:23:00,200
the bears must make do with grass.
284
00:23:11,240 --> 00:23:16,240
Which means the cubs still rely
on their mother's milk
285
00:23:16,320 --> 00:23:17,920
for the bulk of their food.
286
00:23:20,120 --> 00:23:21,280
[Luna groaning]
287
00:23:28,240 --> 00:23:30,760
[pensive music continues]
288
00:23:32,440 --> 00:23:35,440
[cubs purring]
289
00:23:35,520 --> 00:23:39,800
But Luna hasn't eaten properly
since before she went into hibernation,
290
00:23:41,560 --> 00:23:44,040
so she's running on empty.
291
00:23:44,120 --> 00:23:46,520
[Luna breathing heavily]
292
00:23:53,080 --> 00:23:56,040
But nearby, out in space,
293
00:23:57,520 --> 00:23:59,160
help is on the way.
294
00:24:02,360 --> 00:24:04,440
[whooshing]
295
00:24:05,880 --> 00:24:10,400
Because today,
our planet has a constant companion.
296
00:24:10,920 --> 00:24:12,920
[dramatic music playing]
297
00:24:13,000 --> 00:24:14,040
The Moon.
298
00:24:16,320 --> 00:24:18,280
Locked in orbit around the Earth,
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00:24:19,720 --> 00:24:22,320
it's our nearest celestial neighbor.
300
00:24:23,920 --> 00:24:27,960
The largest and brightest object
in the night sky.
301
00:24:32,120 --> 00:24:35,520
And because the Moon
is very big and very close…
302
00:24:37,760 --> 00:24:40,480
it exerts a powerful gravitational pull.
303
00:24:40,560 --> 00:24:42,720
[dramatic music continues]
304
00:24:47,880 --> 00:24:51,480
Strong enough to influence our world.
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00:24:56,080 --> 00:24:59,160
It lifts the oceans away
from the planet's surface…
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00:25:05,880 --> 00:25:07,440
[water rippling]
307
00:25:07,520 --> 00:25:09,680
…creating Earth's tides.
308
00:25:15,960 --> 00:25:18,680
And on a few days
around the full and new Moon…
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00:25:20,800 --> 00:25:25,400
the lowest summer tides reveal
an entirely new landscape.
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00:25:25,480 --> 00:25:27,760
[birds squawking]
311
00:25:29,760 --> 00:25:32,800
Mudflats extend hundreds of meters
from the shore.
312
00:25:38,200 --> 00:25:39,040
[Luna grunts]
313
00:25:39,120 --> 00:25:42,800
Allowing hungry bears access
to buried treasure.
314
00:25:44,440 --> 00:25:47,040
[calm music playing]
315
00:25:50,560 --> 00:25:54,480
At just the right time
for Luna and her young family.
316
00:25:54,560 --> 00:25:56,000
[sniffing]
317
00:26:02,480 --> 00:26:04,720
But finding what's hidden in the mud
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00:26:05,480 --> 00:26:08,200
is a job best left to the grown-ups.
319
00:26:09,680 --> 00:26:11,800
[sniffing]
320
00:26:17,080 --> 00:26:21,680
Luna's sense of smell
is 2,000 times better than our own.
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00:26:24,480 --> 00:26:26,880
Perfect for detecting tasty morsels.
322
00:26:31,200 --> 00:26:32,680
Soft-shelled clams.
323
00:26:32,760 --> 00:26:35,440
[playful music playing]
324
00:26:53,680 --> 00:26:56,200
She's so skilled at prizing them apart,
325
00:26:57,400 --> 00:27:00,200
she can get through almost one a minute.
326
00:27:12,840 --> 00:27:15,080
[sniffing]
327
00:27:20,440 --> 00:27:24,000
The clams are a welcome supplement
to her meager summer diet.
328
00:27:31,720 --> 00:27:34,600
Vital energy
she can pass along to the cubs.
329
00:27:34,680 --> 00:27:38,600
[cubs purring]
330
00:27:39,800 --> 00:27:43,360
These gifts, delivered to her by the Moon,
331
00:27:43,880 --> 00:27:46,760
will help Luna sustain her family
through summer.
332
00:27:49,880 --> 00:27:52,480
But the bear's relationship with the Moon…
333
00:27:52,560 --> 00:27:53,600
[whooshing]
334
00:27:53,680 --> 00:27:55,360
[ethereal music playing]
335
00:27:55,440 --> 00:27:58,440
…runs much, much deeper.
336
00:27:58,520 --> 00:28:00,520
-[Luna groans]
-[whooshing]
337
00:28:01,400 --> 00:28:02,400
[growls]
338
00:28:03,240 --> 00:28:08,280
Because it was during the Moon's formation
that Earth got its seasons.
339
00:28:13,880 --> 00:28:16,040
Not long after it formed,
340
00:28:16,960 --> 00:28:18,760
our planet gained a companion.
341
00:28:22,200 --> 00:28:25,080
[ethereal music playing]
342
00:28:31,000 --> 00:28:32,800
But it wasn't the Moon.
343
00:28:34,920 --> 00:28:39,080
It was another planet
that formed in Earth's orbit.
344
00:28:44,520 --> 00:28:46,880
A sibling called Theia.
345
00:28:48,680 --> 00:28:50,800
It was roughly the size of Mars.
346
00:28:52,760 --> 00:28:56,680
-[lava bubbling, exploding]
-A vast ball of rock and lava.
347
00:28:59,440 --> 00:29:01,200
Throughout their childhood,
348
00:29:03,040 --> 00:29:05,120
Earth and Theia lived in harmony.
349
00:29:05,200 --> 00:29:07,480
[ominous music playing]
350
00:29:11,320 --> 00:29:16,280
Until gravitational disturbances
in the young solar system…
351
00:29:19,680 --> 00:29:23,400
set the two planets on a collision course.
352
00:29:28,880 --> 00:29:30,040
In this moment…
353
00:29:30,800 --> 00:29:31,960
[rumbling]
354
00:29:32,040 --> 00:29:35,040
…Earth's future hangs in the balance.
355
00:29:38,280 --> 00:29:40,680
[rumbling growing louder]
356
00:29:40,760 --> 00:29:42,920
[ominous music intensifies]
357
00:29:45,280 --> 00:29:46,920
[crashing]
358
00:29:54,000 --> 00:29:56,040
Theia is obliterated…
359
00:29:59,480 --> 00:30:02,400
as the impact melts both worlds.
360
00:30:12,280 --> 00:30:14,680
[ethereal music playing]
361
00:30:29,120 --> 00:30:31,400
For an instant in cosmic time…
362
00:30:34,560 --> 00:30:36,480
our planet had two moons.
363
00:30:41,000 --> 00:30:43,680
[fire roaring, crackling]
364
00:30:46,360 --> 00:30:53,160
But then gravity dragged one of them
back down to be consumed by Earth.
365
00:30:54,960 --> 00:30:57,360
[ethereal music continues]
366
00:31:06,720 --> 00:31:09,880
Leaving only the moon we know today.
367
00:31:17,040 --> 00:31:21,160
And the collision transformed
our planet forever.
368
00:31:21,680 --> 00:31:23,240
[whooshing]
369
00:31:23,320 --> 00:31:26,080
[calm music playing]
370
00:31:28,280 --> 00:31:30,600
The impact knocked it over to one side
371
00:31:31,600 --> 00:31:35,040
so that today it spins
with a tilt of 23 degrees.
372
00:31:40,960 --> 00:31:43,760
So, as it moves around in its orbit,
373
00:31:45,600 --> 00:31:47,040
first one hemisphere
374
00:31:47,720 --> 00:31:51,640
then the other is angled toward the Sun…
375
00:31:55,000 --> 00:31:57,880
giving Earth its seasons.
376
00:31:57,960 --> 00:32:00,520
[dramatic music playing]
377
00:32:10,680 --> 00:32:12,760
[owl hooting]
378
00:32:19,600 --> 00:32:21,920
As summer draws to a close,
379
00:32:22,680 --> 00:32:25,200
the longer nights are a sign
380
00:32:25,280 --> 00:32:28,280
that the harsh Alaskan winter
is fast approaching.
381
00:32:32,560 --> 00:32:35,200
The cubs are now seven months old.
382
00:32:41,120 --> 00:32:45,640
And Luna knows that if they are to survive
their long winter sleep,
383
00:32:46,360 --> 00:32:49,400
the family must build up
their fat reserves.
384
00:32:50,760 --> 00:32:51,880
[Luna groans]
385
00:33:03,800 --> 00:33:04,880
[moaning]
386
00:33:06,000 --> 00:33:08,240
But the Moon is a constant reminder…
387
00:33:09,880 --> 00:33:12,400
[bellowing]
388
00:33:12,920 --> 00:33:14,400
…help is on the way.
389
00:33:19,800 --> 00:33:22,960
A thousand kilometers
off the coast of Alaska…
390
00:33:24,960 --> 00:33:28,480
another creature is tuned in
to Earth's seasonal rhythm.
391
00:33:28,560 --> 00:33:30,320
[calm music playing]
392
00:33:32,200 --> 00:33:34,200
Sockeye salmon.
393
00:33:36,760 --> 00:33:39,080
After two years roaming the Pacific Ocean…
394
00:33:40,880 --> 00:33:42,240
[ethereal tinkling]
395
00:33:42,760 --> 00:33:44,120
…they've reached maturity.
396
00:33:46,080 --> 00:33:48,400
And now, the changing day length…
397
00:33:48,480 --> 00:33:49,520
[whooshing]
398
00:33:49,600 --> 00:33:52,680
…triggers hormones
to be released into their blood.
399
00:33:55,720 --> 00:33:59,080
Chemical signals
that alter their behavior.
400
00:33:59,160 --> 00:34:02,080
[whooshing]
401
00:34:03,360 --> 00:34:06,000
[joyful music playing]
402
00:34:08,080 --> 00:34:09,440
Calling them home
403
00:34:10,920 --> 00:34:13,800
to breed in the rivers
where they were born.
404
00:34:20,600 --> 00:34:22,040
[joyful music crescendos]
405
00:34:26,480 --> 00:34:28,160
[pensive music playing]
406
00:34:28,240 --> 00:34:29,440
[groans]
407
00:34:34,280 --> 00:34:36,080
Luna's exhausted and hungry,
408
00:34:37,120 --> 00:34:41,600
but still she leads her cubs
to the river's edge.
409
00:34:42,280 --> 00:34:45,000
[grunting]
410
00:34:54,080 --> 00:34:59,000
Because she senses something magical
is about to happen.
411
00:34:59,080 --> 00:35:00,320
[cub grunts]
412
00:35:04,080 --> 00:35:08,960
Today, the unique clockwork of the seasons
413
00:35:09,040 --> 00:35:12,400
will deliver a vital lifeline
to the bears.
414
00:35:14,880 --> 00:35:17,200
[dramatic music playing]
415
00:35:33,520 --> 00:35:37,680
The Earth has reached a pivotal position
in its journey around the Sun.
416
00:35:41,720 --> 00:35:44,240
And now the Moon raises the tide.
417
00:35:46,560 --> 00:35:47,400
[Luna grunts]
418
00:35:50,000 --> 00:35:55,280
Providing the final push
that drives the salmon into the rivers.
419
00:35:56,480 --> 00:35:58,680
[Luna breathing heavily]
420
00:36:06,280 --> 00:36:08,760
[pensive music playing]
421
00:36:21,280 --> 00:36:22,200
[cub whines]
422
00:36:29,520 --> 00:36:31,880
[playful music playing]
423
00:36:39,080 --> 00:36:40,400
[Luna groans]
424
00:36:40,480 --> 00:36:45,680
At long last,
the cubs get their first taste of salmon.
425
00:36:51,160 --> 00:36:54,960
And although a single fish
will not see the bears through winter,
426
00:36:55,920 --> 00:37:01,400
it's the cubs' first real meal
in nearly eight months of life.
427
00:37:04,040 --> 00:37:06,400
[playful music continues]
428
00:37:15,320 --> 00:37:17,040
[Luna huffing]
429
00:37:18,040 --> 00:37:21,880
The arrival of the first salmon
is a relief to Luna.
430
00:37:24,720 --> 00:37:26,600
Because experience has told her
431
00:37:27,720 --> 00:37:31,200
there will soon be
much richer pickings upstream.
432
00:37:46,440 --> 00:37:47,520
[whooshing]
433
00:37:50,720 --> 00:37:52,720
As the days grow ever shorter,
434
00:37:54,400 --> 00:37:58,280
the very same hormones
that set the salmon off on their journey
435
00:37:59,200 --> 00:38:01,400
now dramatically transform them.
436
00:38:02,400 --> 00:38:04,200
[whooshing]
437
00:38:06,200 --> 00:38:08,880
[calm music playing]
438
00:38:08,960 --> 00:38:10,560
Their heads change shape.
439
00:38:13,000 --> 00:38:15,680
And their bodies blush bright red.
440
00:38:19,040 --> 00:38:20,960
As in their millions,
441
00:38:21,480 --> 00:38:25,920
they surge upriver
into their spawning grounds.
442
00:38:26,000 --> 00:38:28,400
[calm music continues]
443
00:38:36,120 --> 00:38:40,400
And the final piece
of the bears' story falls into place.
444
00:38:49,120 --> 00:38:52,520
A story as old as the planet itself.
445
00:38:53,600 --> 00:38:56,200
[dramatic music playing]
446
00:39:02,680 --> 00:39:04,280
The formation of the Earth…
447
00:39:09,760 --> 00:39:12,040
the collision that created the Moon…
448
00:39:15,000 --> 00:39:18,840
and our planet's unique relationship
with its moon and star…
449
00:39:25,400 --> 00:39:31,520
have combined to create a world
like nowhere else in the universe.
450
00:39:33,920 --> 00:39:35,600
A Goldilocks planet.
451
00:39:38,600 --> 00:39:42,680
The only place we know
that's just right for life.
452
00:39:42,760 --> 00:39:46,200
[dramatic music crescendos]
453
00:40:04,320 --> 00:40:05,360
And for Luna,
454
00:40:06,000 --> 00:40:09,000
four and a half billion years
of cosmic history
455
00:40:10,920 --> 00:40:14,000
is now distilled into this moment.
456
00:40:21,760 --> 00:40:27,200
The annual convergence of salmon and bear.
457
00:40:38,160 --> 00:40:40,400
And the precious opportunity
458
00:40:42,160 --> 00:40:43,440
to feed her family.
459
00:40:47,000 --> 00:40:49,280
[dramatic music playing]
460
00:40:51,120 --> 00:40:55,080
Luna and her cubs now have what they need
to make it through winter.
461
00:40:57,400 --> 00:41:01,960
And while ultimately, their future
on our changing planet is uncertain,
462
00:41:03,320 --> 00:41:06,480
for this year,
the salmon will sustain them…
463
00:41:10,400 --> 00:41:13,120
as our planet continues
on this relentless voyage…
464
00:41:13,200 --> 00:41:15,600
[Luna bellowing]
465
00:41:15,680 --> 00:41:17,000
…around the Sun.
466
00:41:18,000 --> 00:41:19,720
[dramatic music crescendos]
467
00:41:23,920 --> 00:41:26,560
[dramatic music playing]
468
00:41:26,640 --> 00:41:29,720
Next in the story of our universe,
469
00:41:31,160 --> 00:41:34,720
the ocean wanderer
whose life cycle reveals
470
00:41:35,400 --> 00:41:39,320
how everything in the universe was made.
471
00:41:41,120 --> 00:41:43,400
Because in every turtle's egg
472
00:41:44,280 --> 00:41:46,680
are atoms from The Big Bang…
473
00:41:47,480 --> 00:41:48,920
[ethereal tinkling]
474
00:41:49,000 --> 00:41:52,560
…forged as stars die.
475
00:41:53,520 --> 00:41:54,880
[whooshing]
476
00:41:54,960 --> 00:41:56,080
[exploding]
477
00:41:56,160 --> 00:41:59,000
But how are stars and planets created?
478
00:42:00,840 --> 00:42:07,080
And how do the same ingredients
transform into living things?
479
00:42:14,440 --> 00:42:18,360
[dramatic music playing]