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-- How the Universe Works - S08E09 --
1080p HDTV x264 AAC
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Narrator: The earth is taking us on the ride of our lives,
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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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that's on top of a high-speed train.
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Narrator: Now we're unlocking the secrets
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of our planet's voyage and discovering that earth's journey
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affects us all.
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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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Narrator: But the ride can be dangerous...
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...plunging our planet into the deep freeze...
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...putting us in the path of supernovas,
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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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We are earth's passengers as our home planet
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travels through the cosmos.
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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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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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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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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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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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Narrator: Life evolved in lockstep
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with earth's spinning motion.
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But in the ocean, corals take things a step further
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by keeping a record of every planetary turn.
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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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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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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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Narrator: When the ancient corals were alive,
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there were 420 days in one earth year,
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meaning a day was just 21 hours long.
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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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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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Collisions were frequent.
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One giant impact set our planet spinning rapidly...
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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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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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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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and when these rocks hit the earth,
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they almost never hit directly on.
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They'd hit at an angle.
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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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The added spin that you get is a kind of like a merry-go-round.
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You can imagine with each kid that pushes and jumps
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on the merry-go-round, you have greater spin.
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Narrator: As our planet journeyed on, asteroid impacts
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set the young earth
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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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actually has an effect on our weather.
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With a shorter day,
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one of the effects that might have been apparent on earth
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at that time was more storms developing.
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Narrator: A phenomenon still in action today
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drove these powerful ancient storms.
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We call it the Coriolis effect.
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The earth's spin creates phenomena
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in earth's atmosphere and oceans.
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This determines patterns of circulation
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in combination with the heat energy from the sun.
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The rotation of the earth matched with solar heating,
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especially at the equator, causes air to rise up
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and then also sort of to move sideways and sets up spin.
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Narrator: As the young earth continued its journey,
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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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The storms would have been so big,
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it's hard to say if life would have evolved at all.
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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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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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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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and life arose.
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As earth's spin continued to slow down,
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life spread across the planet.
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But our planet's spin is just one part of our cosmic ride.
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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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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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Narrator: The sahara desert -- dry, dusty, desolate.
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But hidden deep in a desert cave
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is a clue that thousands of years ago,
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the sahara was a lush, green paradise.
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Archaeologists have unearthed rock art
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which clearly depicts humans and animals swimming in lakes,
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and by looking at satellite images,
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we can trace out the outlines of ancient river valleys.
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Narrator: The earth's fast rotation influenced
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our planet's ancient weather patterns.
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Could another motion have changed the desert climate?
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To unravel the mystery, we need to rewind the clock
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4.6 billion years
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to when the infant solar system
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was a planetary shooting gallery
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and the earth spun through the solar system with a slight tilt.
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Earlier on, before the formation of the moon,
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the earth didn't have much of a tilt,
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and the impact knocked us completely out of whack
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to about 80 degrees.
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Narrator: Our planet might have continued its journey
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tilted right over, but over billions of years,
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the moon's gravity pulled the earth upright,
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just not completely.
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The moon is not quite in the equatorial plane of the earth.
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It's above the equatorial plane,
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and it pulls the earth's axis into a 23 1/2-degree tilt.
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Stricker: If we didn't have the tilt to about 23 degrees,
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then we wouldn't have the seasons,
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and these seasons drive a lot of the crops and the growth
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and the ability to survive all across the globe.
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Narrator: But the ancient greening of the sahara
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can't be explained by the changing seasons.
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Another planetary motion must be in play.
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A clue is found in the night sky --
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the north star.
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Right now, the earth's axis is pointed towards a star
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in the sky called the north star -- polaris.
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We've actually named it after the fact
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that the north pole of the earth points toward it in the sky.
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Narrator: But polaris hasn't always been the north star.
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5,000 years ago, it was a totally different star.
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It was Thuban, which is in Draco,
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a different constellation.
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Sometime in the future, it'll be Vega,
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the brightest star in the constellation Lyra,
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so the north star actually changes
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because the north pole's position in the sky changes.
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Narrator: The changing pole star is evidence
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that earth is wobbling through space.
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It's a process called precession,
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something that also affects spinning tops.
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Plait: If you take a top and let it spin really rapidly
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and poke it,
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the axis of rotation will spin around like this,
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and it's much slower than the actual spin of the object.
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That is precession, this circle that the axis is making.
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This happens to the earth, as well.
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Narrator: A cosmic poke caused earth's space wobble,
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but what has the power to poke a planet?
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Once again, the key is gravity,
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this time earth's gravitational interactions
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with the moon and sun.
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These forces are that poke on the spinning earth,
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and that's what makes the earth's axis spin in precession,
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and it takes about 20,000 years to make a complete circle once.
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Narrator: As the earth continues its journey around the sun,
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this precession changes the planet's climate dramatically.
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When the earth's north pole leans toward the sun,
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northern hemisphere summers are sunnier...
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with unexpected consequences for the sahara.
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Rampino: It turns out that at times when
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the climate in the sahara gets more sunshine,
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that warms the climate up,
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and the winds come in from the ocean.
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It's called the monsoon effect and brings water --
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rain into the sahara, where now it's dry.
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Olsen: This pattern of wet and dry climates
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that produce this 20,000-year cycle
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is what we see in the sahara,
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where at times of strong monsoon,
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the sahara is wetter, a green sahara.
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Narrator: 10,000 years ago,
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as the earth wobbled around the sun,
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monsoons were unleashed, turning the desert green.
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Humans migrated to the newly lush sahara
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and created the cave paintings we see today.
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But this wasn't the first time humans crossed a green sahara.
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Dartnell: A dry sahara would have presented
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an insurmountable barrier
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to our ancestors for migrating out of africa,
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but during one of these cycles when the sahara was green,
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it would have been a corridor
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that we could have migrated and dispersed on.
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Narrator: As the earth traveled the cosmos,
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our planet's precession changed the sahara
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and the fate of humankind, but there are more cosmic forces
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affecting our journey through the universe.
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The earth's orbit around the sun is another thing
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that seems very, very solid.
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We understand how it works, but everything in the universe
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is a delicately tuned dance of gravity,
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and things can change even from tiny little influences.
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Narrator: As our planet hurtles through space,
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other worlds influence our path.
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Could a planetary bully push earth's climate to the extreme?
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Narrator: Earth carries us on a wild journey through the cosmos.
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And clues to the effects of this trip
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are hiding in our own backyard.
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In new york city, amongst the buildings and traffic,
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we find moraines,
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rocks left behind by retreating glaciers.
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18,000 years ago,
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a sheet of ice taller than any skyscraper covered manhattan.
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Ice ages have struck regularly throughout earth's history,
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putting our planet in a deep freeze.
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Durda: There was a period in earth's history
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several hundred million years ago,
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the snowball earth period,
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when we went through a very extreme glaciation,
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if you will, a very extreme ice age
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where we think perhaps the entire earth
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was covered in an ice sheet.
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Narrator: The trigger?
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Earth's orbital dance around the sun.
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We tend to think of ourselves
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sitting relatively stationary on the earth.
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It's pretty comforting, actually,
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but we're orbiting the sun at about 66,000 miles per hour.
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Narrator: Every day, earth travels over 1.6 million miles
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on its journey around the sun.
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This orbit isn't always completely round.
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Earth is generally going around the sun
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in more or less a circular orbit,
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but over time, the massaging of this orbit from the sun,
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from the moon on the earth's orbit
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causes the orbit of the earth to change
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so that sometimes it's an ellipse.
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Sometimes it's more of a circle.
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Right now on the earth,
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we're in kind of the most circular time in the orbit,
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so that means the summers are relatively mild,
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and the winters are relatively mild,
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but imagine not that long ago in the past,
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it could have been really dramatically different.
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When the earth is a little bit closer to the sun,
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maybe you have a really severe summer,
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and then on the other side of the orbit,
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you're a little farther away from the sun than normal,
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so you have a really severe winter.
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Our environment is very, very sensitive to these things,
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and when the earth's orbit is stretched out,
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that can actually trigger an ice age.
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Narrator: Our planet's 100,000-year orbital cycle
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caused the ice age that buried New York.
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And ice ages have had a big effect on human history.
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15,000 years ago,
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plunging temperatures locked water away
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in glaciers and ice caps.
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Sea levels dropped, creating land bridges between continents.
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Humans migrated from asia to america by foot,
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and for the first time, America was inhabited.
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May 2018 -- scientists revealed a whole new dynamic
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to earth's journey.
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Every 405,000 years,
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our planet's orbital voyage stretches to the extreme,
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and earth's planetary neighbors are to blame.
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Because Jupiter is the most massive planet
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in our solar system,
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it is in many ways the bully on the playground, right?
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Its dynamics, its gravity sculpts a lot of the dynamics
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of the solar system.
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Durda: It actually tugs and pulls on the orbit
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of the earth itself.
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It's responsible for some of the very changes
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that drive our climatic cycle here on our planet.
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Narrator: Jupiter isn't the only bully in the playground.
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Thaller: Venus is a fairly big planet
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about the size of the earth
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and also comes closest to us in its orbit,
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so these two planets put just a little tiny elongation
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onto our earth's orbit,
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and as the cycle continues, the more extreme it gets,
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we can actually notice a temperature difference
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that happens about once every 405,000 years.
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Narrator: Jupiter and venus gang up on earth gravitationally,
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pulling earth's orbit into an even greater ellipse.
335
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Our planet's hot weather becomes hotter,
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and its cold weather gets much colder.
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Today, we're in a moderate part of the cycle,
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but in just 60,000 years time,
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we could plunge into another deep freeze.
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It's a little bit like a cosmic butterfly effect.
341
00:22:16,069 --> 00:22:18,235
I mean, even the smallest effects
342
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can have, you know, a big influence over time.
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Narrator: Earth's orbit around the sun
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is just part of our far larger cosmic journey.
345
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The entire solar system is hurtling around the milky way,
346
00:22:38,858 --> 00:22:43,227
taking us places we don't want to be.
347
00:22:43,229 --> 00:22:45,796
Sometimes our planet might wander
348
00:22:45,798 --> 00:22:48,466
into what's essentially a bad neighborhood.
349
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Narrator: What dangers await us?
350
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And could these neighborhoods spell disaster
351
00:22:53,673 --> 00:22:55,272
for life on earth?
352
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Narrator: Over the last 3.7 billion years,
353
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a series of extinction events wiped out
354
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almost 95 percent of all species on earth.
355
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Now research suggests our planet's orbit
356
00:23:30,910 --> 00:23:33,277
could be partly to blame,
357
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but not the earth's orbit around the sun,
358
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our planet's larger and longer journey around the milky way.
359
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Our solar system and our sun is shooting through the galaxy
360
00:23:45,458 --> 00:23:51,395
at about 530,000 miles per hour around the center of our galaxy.
361
00:23:51,397 --> 00:23:54,665
And that center of the galaxy is about 26,000 light-years away,
362
00:23:54,667 --> 00:23:57,735
so it should take the sun about 230 million years
363
00:23:57,737 --> 00:24:01,038
to trace out one full orbit around the center of the galaxy.
364
00:24:03,576 --> 00:24:05,609
Narrator: Despite racing around the milky way
365
00:24:05,611 --> 00:24:08,913
at 1/2 million miles an hour,
366
00:24:08,915 --> 00:24:12,716
earth has completed less than 20 laps of the galaxy
367
00:24:12,718 --> 00:24:16,520
in our planet's entire history,
368
00:24:16,522 --> 00:24:19,990
and it turns out this galactic ride
369
00:24:19,992 --> 00:24:22,860
is more complicated than it seems.
370
00:24:22,862 --> 00:24:24,995
Now, if you look at the earth going around the sun,
371
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it defines an ellipse,
372
00:24:26,432 --> 00:24:28,933
but that's a flat figure, and you'd think,
373
00:24:28,935 --> 00:24:32,336
"well, the sun probably goes around in a plane, as well,"
374
00:24:32,338 --> 00:24:34,805
and it turns out not that simple.
375
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Narrator: Most of the mass of the solar system
376
00:24:39,779 --> 00:24:42,079
is concentrated in the sun,
377
00:24:42,081 --> 00:24:46,784
so earth and the other planets smoothly orbit our star.
378
00:24:50,189 --> 00:24:55,359
But the mass of the milky way is spread out unevenly.
379
00:24:55,361 --> 00:24:57,862
That changes the gravity of the galaxy,
380
00:24:57,864 --> 00:25:00,831
and so it changes how things move in it, and in fact,
381
00:25:00,833 --> 00:25:03,934
if you give something a little bit of an up or down motion,
382
00:25:03,936 --> 00:25:07,371
it'll bob up and down as it goes around.
383
00:25:07,373 --> 00:25:10,574
Oluseyi: Riding the earth is almost like riding a carousel.
384
00:25:10,576 --> 00:25:13,477
As the sun and the earth go around the galaxy,
385
00:25:13,479 --> 00:25:15,246
the sun also goes up and down
386
00:25:15,248 --> 00:25:17,381
like you're on one of those horses with the pole,
387
00:25:17,383 --> 00:25:19,049
and so what this can do
388
00:25:19,051 --> 00:25:22,820
is take us into different galactic environments.
389
00:25:26,158 --> 00:25:29,426
Narrator: This bobbing motion takes earth and the solar system
390
00:25:29,428 --> 00:25:31,662
on a 60,000-year journey
391
00:25:31,664 --> 00:25:35,432
up and down through the milky way's galactic plane.
392
00:25:37,870 --> 00:25:39,370
Our orbit also takes us
393
00:25:39,372 --> 00:25:41,872
through different galactic neighborhoods.
394
00:25:45,378 --> 00:25:50,948
Today, we're traveling through a calm suburb of the galaxy.
395
00:25:50,950 --> 00:25:55,352
But sometimes things get a little bumpy.
396
00:25:55,354 --> 00:25:59,089
Sometimes our sun and our planet might wander
397
00:25:59,091 --> 00:26:01,659
into what's essentially a bad neighborhood.
398
00:26:01,661 --> 00:26:02,993
You know, maybe it's an area
399
00:26:02,995 --> 00:26:04,962
where there's a lot of star formation going on,
400
00:26:04,964 --> 00:26:07,898
where there's a lot of young stars that are very active,
401
00:26:07,900 --> 00:26:11,101
or maybe it's a location where there are dying stars,
402
00:26:11,103 --> 00:26:14,104
and things are about to get really hot.
403
00:26:14,106 --> 00:26:16,774
Narrator: The baddest neighborhoods in the galaxy
404
00:26:16,776 --> 00:26:19,310
may be the spiral arms.
405
00:26:21,847 --> 00:26:25,282
These gas-filled regions orbit the galactic center
406
00:26:25,284 --> 00:26:28,819
more slowly than the earth,
407
00:26:28,821 --> 00:26:31,989
so our planet passes through an arm
408
00:26:31,991 --> 00:26:35,559
roughly every 150 million years.
409
00:26:35,561 --> 00:26:39,296
Plait: These arms are where gas clouds tend to hang out,
410
00:26:39,298 --> 00:26:43,834
and if they get compressed, they form a lot of stars.
411
00:26:43,836 --> 00:26:48,205
When they form a lot of stars, they make bright, blue stars.
412
00:26:48,207 --> 00:26:51,642
And they don't last long, and they blow up as supernova.
413
00:27:00,353 --> 00:27:03,887
So it's possible that as we're passing through these regions,
414
00:27:03,889 --> 00:27:06,824
these are places you might not want to be in,
415
00:27:06,826 --> 00:27:08,225
so in the distant past,
416
00:27:08,227 --> 00:27:10,127
this may have affected the earth.
417
00:27:15,434 --> 00:27:17,501
Narrator: When giant stars go supernova,
418
00:27:17,503 --> 00:27:20,237
the stars' outer layers blast into space
419
00:27:23,909 --> 00:27:25,409
along with a shock wave
420
00:27:25,411 --> 00:27:28,212
traveling at 20,000 miles a second.
421
00:27:31,617 --> 00:27:37,154
Supernovas also release cosmic rays --
422
00:27:37,156 --> 00:27:39,890
space bullets that shoot across the galaxy
423
00:27:39,892 --> 00:27:41,792
at close to the speed of light.
424
00:27:44,463 --> 00:27:46,630
Plait: And you don't want to be exposed to too many of them,
425
00:27:46,632 --> 00:27:47,998
but in high enough doses,
426
00:27:48,000 --> 00:27:50,634
these things penetrate our cells and damage our dna
427
00:27:50,636 --> 00:27:54,538
and over the long-term can cause really bad damage
428
00:27:54,540 --> 00:27:57,074
to human bodies.
429
00:27:57,076 --> 00:27:58,676
Narrator: As we ride through space,
430
00:27:58,678 --> 00:28:04,782
earth's magnetic field protects us from most cosmic rays.
431
00:28:04,784 --> 00:28:08,719
But in 2018, we discovered evidence
432
00:28:08,721 --> 00:28:10,688
that a hail of space bullets
433
00:28:10,690 --> 00:28:15,559
overwhelmed our planet's magnetic field in the past.
434
00:28:15,561 --> 00:28:17,561
In many ways, we really take for granted
435
00:28:17,563 --> 00:28:20,631
how the earth protects us from space,
436
00:28:20,633 --> 00:28:22,199
but there are records that we've actually bounced
437
00:28:22,201 --> 00:28:25,869
a little too close to exploding stars.
438
00:28:25,871 --> 00:28:28,005
Plait: Sediments in the ocean show that
439
00:28:28,007 --> 00:28:30,107
about 2 million years ago,
440
00:28:30,109 --> 00:28:33,310
iron-60 was deposited in our oceans.
441
00:28:33,312 --> 00:28:36,046
Iron-60 is a radioactive isotope of iron,
442
00:28:36,048 --> 00:28:38,749
and there's only way we know of it being made in the universe,
443
00:28:38,751 --> 00:28:41,351
and that is exploding stars.
444
00:28:45,691 --> 00:28:47,725
Narrator: Around 2.8 million years ago,
445
00:28:47,727 --> 00:28:52,162
a supernova exploded just 150 light-years from earth.
446
00:28:54,567 --> 00:28:56,200
A few hundred years later,
447
00:28:56,202 --> 00:29:00,104
a blizzard of cosmic rays slammed into the earth,
448
00:29:00,106 --> 00:29:02,406
tearing through our magnetic field.
449
00:29:06,445 --> 00:29:10,481
These space bullets are prime suspect in the extinction
450
00:29:10,483 --> 00:29:13,450
of over 1/3 of all coastal marine species.
451
00:29:16,122 --> 00:29:18,422
Plait: Now, this is not necessarily tied to the earth
452
00:29:18,424 --> 00:29:21,125
passing through one of these spiral arms,
453
00:29:21,127 --> 00:29:23,861
but it shows you that being close to a supernova
454
00:29:23,863 --> 00:29:28,098
is not necessarily a thing you want to do.
455
00:29:28,100 --> 00:29:30,067
Narrator: Millions of years in the future,
456
00:29:30,069 --> 00:29:33,637
earth will pass through another spiral arm
457
00:29:33,639 --> 00:29:39,409
as our planet continues its journey through the milky way.
458
00:29:39,411 --> 00:29:43,781
And we will wander into harm's way once again.
459
00:29:46,619 --> 00:29:49,019
But there's another part of our journey through space
460
00:29:49,021 --> 00:29:51,889
that remains a mystery.
461
00:29:51,891 --> 00:29:54,825
The earth is spinning like a top on its axis.
462
00:29:54,827 --> 00:29:56,260
It's orbiting around the sun.
463
00:29:56,262 --> 00:29:58,662
The sun itself is orbiting around the center
464
00:29:58,664 --> 00:30:03,500
of the milky way, but that's far from it.
465
00:30:03,502 --> 00:30:06,170
Narrator: The milky way is speeding through the universe,
466
00:30:06,172 --> 00:30:11,375
and we are being dragged along for the ride.
467
00:30:11,377 --> 00:30:14,912
The problem is we can't see where we're going.
468
00:30:14,914 --> 00:30:18,582
Could earth be headed for a galactic crash?
469
00:30:32,765 --> 00:30:35,399
Narrator: Like the craziest of theme park rides,
470
00:30:35,401 --> 00:30:39,703
we are riding the earth on a wild journey through the cosmos.
471
00:30:46,445 --> 00:30:50,981
Our planet spins, tilts, and wobbles around the solar system
472
00:30:53,118 --> 00:30:56,720
while bobbing like a carousel through the milky way.
473
00:30:59,225 --> 00:31:03,026
The dynamics of the earth moving in the cosmic void is,
474
00:31:03,028 --> 00:31:06,697
like, the most unbelievable journey you could ever imagine,
475
00:31:06,699 --> 00:31:08,699
and as you get to larger scales,
476
00:31:08,701 --> 00:31:12,169
the motions only become grander and larger and more dynamic.
477
00:31:16,041 --> 00:31:19,176
Narrator: In 1977, we tried to work out
478
00:31:19,178 --> 00:31:21,078
the largest motion of all --
479
00:31:23,649 --> 00:31:27,851
the movement of our galaxy through the universe.
480
00:31:27,853 --> 00:31:31,154
Clues hide in the cosmic microwave background,
481
00:31:31,156 --> 00:31:34,524
a remnant from the birth of the universe.
482
00:31:34,526 --> 00:31:37,094
Bullock: The cosmic microwave background is the radiation
483
00:31:37,096 --> 00:31:40,397
that's left over from the hot big bang.
484
00:31:40,399 --> 00:31:43,166
The cosmic microwave background is shining in all directions
485
00:31:43,168 --> 00:31:44,902
as sort of this fixed thing,
486
00:31:44,904 --> 00:31:47,337
and if we're moving through it with some speed,
487
00:31:47,339 --> 00:31:49,373
we will see that in the light itself.
489
00:31:49,375 --> 00:31:51,275
You can measure that, and by measuring that,
490
00:31:51,277 --> 00:31:55,946
you can get a sense of how fast we're moving through that space.
491
00:31:55,948 --> 00:31:58,115
Narrator: By tracking our movement through the universe
492
00:31:58,117 --> 00:31:59,716
against a fixed point,
493
00:31:59,718 --> 00:32:03,553
we can work out the milky way's speed and direction.
494
00:32:06,392 --> 00:32:13,030
But in 1977, telescopes weren't the best tool for the job.
495
00:32:13,032 --> 00:32:15,565
Tremblay: During the cold war, 1977,
496
00:32:15,567 --> 00:32:18,201
you have the newly declassified U-2 spy plane,
497
00:32:18,203 --> 00:32:21,238
this very high-altitude reconnaissance aircraft.
498
00:32:21,240 --> 00:32:24,775
Nasa retrofitted one of them with an upward-facing window,
499
00:32:24,777 --> 00:32:26,710
and with very sensitive receivers,
500
00:32:26,712 --> 00:32:29,379
this spy plane became the first experiment
501
00:32:29,381 --> 00:32:32,849
to for the first time definitively measure the motion
502
00:32:32,851 --> 00:32:35,018
of the galaxy through the universe.
503
00:32:35,020 --> 00:32:38,121
Narrator: As the U-2 spy plane soared above the earth,
504
00:32:38,123 --> 00:32:41,024
it measured the cosmic microwave background
505
00:32:41,026 --> 00:32:42,893
in unprecedented detail.
506
00:32:46,098 --> 00:32:49,366
The data revealed that our galaxy races
507
00:32:49,368 --> 00:32:53,537
through the universe at 370 miles a second.
508
00:32:57,376 --> 00:32:59,476
That's over 1 million miles an hour.
509
00:33:03,349 --> 00:33:05,949
sutter: Think of how big a galaxy is.
510
00:33:05,951 --> 00:33:08,819
Hundreds of millions of stars,
511
00:33:08,821 --> 00:33:12,622
and we're moving at hundreds of miles per second.
512
00:33:12,624 --> 00:33:14,725
That's just a tiny bit mind-blowing.
513
00:33:16,862 --> 00:33:20,130
Narrator: The milky way's speed isn't the most alarming part
514
00:33:20,132 --> 00:33:22,766
of our galactic journey.
515
00:33:22,768 --> 00:33:26,703
From earth, we can't even see in the direction our galaxy
516
00:33:26,705 --> 00:33:28,071
is taking us.
517
00:33:28,073 --> 00:33:29,639
We're flying blind.
518
00:33:29,641 --> 00:33:33,110
Our view is blocked by the milky way itself.
519
00:33:36,081 --> 00:33:38,682
so if you're actually looking through the plane of the galaxy,
520
00:33:38,684 --> 00:33:40,584
through the plane of the pancake,
521
00:33:40,586 --> 00:33:43,220
your view of the galaxy is obscured
522
00:33:43,222 --> 00:33:47,924
by curtains of dust and gas that envelop our solar system.
523
00:33:47,926 --> 00:33:49,726
Bullock: It's very bright. There's a lot of stars.
524
00:33:49,728 --> 00:33:53,130
And our view is blocked by the galaxy itself,
525
00:33:53,132 --> 00:33:56,166
so there's a zone directly behind the galaxy
526
00:33:56,168 --> 00:33:58,402
as we look towards the galactic center
527
00:33:58,404 --> 00:34:00,270
that's really an unknown area.
528
00:34:00,272 --> 00:34:02,305
It's a zone we call the zone of avoidance,
529
00:34:02,307 --> 00:34:05,075
and it's an area of really cosmic mystery.
530
00:34:07,312 --> 00:34:11,081
Narrator: Thanks to this mysterious zone,
531
00:34:11,083 --> 00:34:14,851
we thought we could be headed for a galactic car crash.
532
00:34:20,325 --> 00:34:22,459
Then we had a breakthrough.
533
00:34:28,667 --> 00:34:31,268
We used powerful radio telescopes
534
00:34:31,270 --> 00:34:33,570
to look through the zone of avoidance
535
00:34:33,572 --> 00:34:35,072
for the first time.
536
00:34:41,680 --> 00:34:44,247
Bullock: One of the nice things about using light that's
537
00:34:44,249 --> 00:34:47,784
in the radio is that this kind of light actually can go through
538
00:34:47,786 --> 00:34:50,353
pretty dense kinds of gas and stars
539
00:34:50,355 --> 00:34:53,757
and allows us to sort of look through things.
540
00:34:53,759 --> 00:34:55,926
Using these radio telescopes has given us a glimpse
541
00:34:55,928 --> 00:35:00,530
into what lies beyond the zone of avoidance.
542
00:35:00,532 --> 00:35:03,366
Narrator: Peering through the zone of avoidance,
543
00:35:03,368 --> 00:35:07,070
we found that the milky way's path is clear,
544
00:35:07,072 --> 00:35:08,872
but that's not all.
545
00:35:08,874 --> 00:35:12,442
We also discovered we are just one tiny part
546
00:35:12,444 --> 00:35:14,978
of a vast cluster of galaxies
547
00:35:14,980 --> 00:35:18,081
sailing through the cosmos together.
548
00:35:18,083 --> 00:35:20,383
We think that our galaxy, the milky way,
549
00:35:20,385 --> 00:35:24,354
is part of a much grander cosmic flow of galaxies,
550
00:35:24,356 --> 00:35:26,056
and it is part of what might be
551
00:35:26,058 --> 00:35:28,391
the Laniakea supercluster of galaxies,
552
00:35:28,393 --> 00:35:30,861
this giant, giant cosmic structure
553
00:35:30,863 --> 00:35:33,463
filled with potentially thousands of galaxies
554
00:35:33,465 --> 00:35:35,565
that is moving together in this beautiful,
555
00:35:35,567 --> 00:35:37,400
like, slow-moving river
556
00:35:37,402 --> 00:35:40,437
that is sculpted and dictated by gravity itself.
557
00:35:43,208 --> 00:35:47,043
Narrator: Earth voyages through space along gravitational rivers
558
00:35:47,045 --> 00:35:50,680
hundreds of millions of light-years long
559
00:35:50,682 --> 00:35:54,618
along with a fleet of 100,000 other galaxies,
560
00:35:54,620 --> 00:35:58,622
all moving toward a single point in space,
561
00:35:58,624 --> 00:36:04,728
a gravitational drain known as the great attractor.
562
00:36:04,730 --> 00:36:10,500
Sutter: The great attractor is the local region of gravity,
563
00:36:10,502 --> 00:36:13,670
of strong gravity in this patch of the universe.
564
00:36:13,672 --> 00:36:16,973
It's where all the galaxies in this chunk of the universe
565
00:36:16,975 --> 00:36:20,043
are flowing towards.
566
00:36:20,045 --> 00:36:22,812
At the location of the great attractor
567
00:36:22,814 --> 00:36:23,980
is a bunch of material --
568
00:36:23,982 --> 00:36:25,882
a bunch of gas, a bunch of galaxies,
569
00:36:25,884 --> 00:36:29,085
an extremely massive cluster,
570
00:36:29,087 --> 00:36:33,290
and over time, more and more galaxies
571
00:36:33,292 --> 00:36:35,659
add themselves to this cluster
572
00:36:35,661 --> 00:36:40,230
as they continue to join the great attractor.
573
00:36:40,232 --> 00:36:42,933
Narrator: It's unlikely earth will ever reach
574
00:36:42,935 --> 00:36:45,669
the great attractor.
575
00:36:45,671 --> 00:36:52,442
It seems the milky way is headed for a collision after all.
576
00:36:52,444 --> 00:36:55,579
Is this how our cosmic journey ends?
577
00:37:06,892 --> 00:37:08,959
Narrator: Earth's voyage across the cosmos
578
00:37:08,961 --> 00:37:12,762
has lasted for 4.5 billion years.
579
00:37:17,636 --> 00:37:21,938
The big question -- how will our journey finally end?
580
00:37:25,010 --> 00:37:27,043
a clue comes from the milky way's
581
00:37:27,045 --> 00:37:31,114
traveling companion -- another galaxy, andromeda,
582
00:37:34,586 --> 00:37:37,320
filled with up to a trillion stars
583
00:37:37,322 --> 00:37:40,090
that's charting a similar path to us.
584
00:37:44,997 --> 00:37:47,897
The Andromeda galaxy is another big spiral galaxy,
585
00:37:47,899 --> 00:37:49,532
a lot like our milky way,
586
00:37:49,534 --> 00:37:54,604
and it turns out the two of us are heading for each other.
587
00:37:54,606 --> 00:37:56,640
Narrator: Andromeda and the milky way
588
00:37:56,642 --> 00:38:00,677
are currently 2.5 million light-years apart,
589
00:38:00,679 --> 00:38:03,280
but they're hurtling towards each other
590
00:38:03,282 --> 00:38:06,016
at over 250,000 miles an hour.
591
00:38:08,820 --> 00:38:12,255
A collision is inevitable.
592
00:38:12,257 --> 00:38:13,923
Stricker: Galaxies colliding with each other
593
00:38:13,925 --> 00:38:15,759
sounds like science fiction,
594
00:38:15,761 --> 00:38:17,861
but the collision of the andromeda galaxy
595
00:38:17,863 --> 00:38:22,565
and the milky way galaxy will be a spectacular event.
596
00:38:22,567 --> 00:38:25,101
Oluseyi: When the andromeda and milky way galaxies collide,
597
00:38:25,103 --> 00:38:28,872
it's gonna be a ridiculous light show.
598
00:38:28,874 --> 00:38:32,876
The stars don't collide, but the giant clouds of gas do,
599
00:38:32,878 --> 00:38:35,111
and that's gonna trigger star formation,
600
00:38:35,113 --> 00:38:38,381
so we're gonna have what's known as a starburst galaxy.
601
00:38:40,519 --> 00:38:43,453
When Andromeda finally merges with the milky way,
602
00:38:43,455 --> 00:38:45,488
all bets are off.
603
00:38:45,490 --> 00:38:48,525
All of a sudden, a system of hundreds of billions of stars
604
00:38:48,527 --> 00:38:52,362
will be added to our own, and there will be mass chaos,
605
00:38:52,364 --> 00:38:54,130
but one thing you can guarantee --
606
00:38:54,132 --> 00:38:56,633
there is going to be celestial fireworks.
607
00:38:59,871 --> 00:39:02,939
Narrator: This could be the biggest light show in history,
608
00:39:02,941 --> 00:39:07,911
resulting in the creation of a brand-new galaxy.
609
00:39:07,913 --> 00:39:11,214
We will have become one giant galaxy.
610
00:39:11,216 --> 00:39:13,483
Call it milkdromeda, if you will,
611
00:39:13,485 --> 00:39:15,251
so we will look very different.
612
00:39:15,253 --> 00:39:18,822
Our grand-design, spiral milky way galaxy
613
00:39:18,824 --> 00:39:21,891
will have probably transformed itself
614
00:39:21,893 --> 00:39:26,296
into an entirely different shape.
615
00:39:26,298 --> 00:39:28,531
Narrator: The merging galaxies could create
616
00:39:28,533 --> 00:39:31,668
a giant, elliptical-shaped galaxy,
617
00:39:31,670 --> 00:39:35,271
but earth might not be around to see it.
618
00:39:35,273 --> 00:39:38,742
Billions of stars are gonna come careening into our galaxy,
619
00:39:38,744 --> 00:39:43,012
very, very easily disrupting the orbit of the earth.
620
00:39:43,014 --> 00:39:46,049
The sun could be thrown out of the galaxy entirely.
621
00:39:49,821 --> 00:39:53,289
Narrator: As stars, dust, and gas swirl around each other,
622
00:39:55,961 --> 00:40:00,096
gravitational interactions could slingshot our solar system
623
00:40:00,098 --> 00:40:02,799
out into intergalactic space.
624
00:40:08,206 --> 00:40:10,206
We'll still orbit the sun, and everything will be fine,
625
00:40:10,208 --> 00:40:11,841
kind of, but it just means
626
00:40:11,843 --> 00:40:14,110
we'll see something very different in our sky
627
00:40:14,112 --> 00:40:19,215
in 4.6 billion years than we do now.
628
00:40:19,217 --> 00:40:20,683
Narrator: Our planet could be sent
629
00:40:20,685 --> 00:40:23,686
on a whole new intergalactic ride,
630
00:40:25,724 --> 00:40:32,695
shot out into the cosmos, away from the new milkdromeda galaxy.
631
00:40:32,697 --> 00:40:35,098
There's no way of knowing exactly what's going to happen,
632
00:40:35,100 --> 00:40:38,101
and in that sense, journey's end...
633
00:40:42,274 --> 00:40:43,873
we'll just have to wait and see.
634
00:40:51,416 --> 00:40:53,850
Narrator: We might not know the final destination
635
00:40:53,852 --> 00:40:57,887
for earth's cosmic journey, but we do know this --
636
00:40:57,889 --> 00:41:02,425
so far, it has been an incredible ride.
637
00:41:02,427 --> 00:41:04,594
We've had a fantastic journey
638
00:41:04,596 --> 00:41:07,897
over the history of earth's existence.
639
00:41:07,899 --> 00:41:11,234
We may not be immediately aware of our motions
640
00:41:11,236 --> 00:41:14,437
through the universe, but that doesn't mean they're not there.
641
00:41:16,808 --> 00:41:18,508
Many people think of the earth
642
00:41:18,510 --> 00:41:23,079
as this blue, calm marble in space.
643
00:41:23,081 --> 00:41:26,216
But in reality, it's violently ripping around the sun,
644
00:41:26,218 --> 00:41:28,952
and the sun is ripping about the galaxy.
645
00:41:31,256 --> 00:41:33,456
There's a lot of dynamics happening.
646
00:41:35,527 --> 00:41:37,293
It boggles the mind just to think
647
00:41:37,295 --> 00:41:41,664
of what the earth will have done.
648
00:41:41,666 --> 00:41:44,767
The earth will have actually orbited the sun
649
00:41:44,769 --> 00:41:46,202
10 billion times.
650
00:41:46,204 --> 00:41:49,606
It will have spun on its axis, like, a trillion times
651
00:41:49,608 --> 00:41:52,408
in a galaxy that's moving through space.
652
00:41:55,547 --> 00:41:58,781
riding the earth is anything but a boring trip.
653
00:41:58,783 --> 00:42:03,520
♪ ♪ ♪ ♪