How the Universe Works - S08E09 - Earth's Death Orbit
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00:00The Earth is taking us on the ride of our lives, hurdling through space in ways we never
00:11imagined.
00:12The Earth is extremely dynamic.
00:14It is spinning on its axis, it's whirling about the sun, it's corkscrewing throughout
00:20this galaxy.
00:22It's just never a dull moment.
00:24It's like doing a waltz on top of a carousel that's on top of a high-speed train.
00:30Now we're unlocking the secrets of our planet's voyage and discovering that Earth's journey
00:38affects us all.
00:41We see evidence of this motion everywhere we look, not just in the motions of objects
00:46in the sky, but in the land and the seas themselves.
00:51Life on Earth wouldn't be the same if we didn't find ourselves in this dramatic environment
00:55in space.
00:58But the ride can be dangerous, plunging our planet into the deep freeze, putting us in
01:11the path of supernovae, pulling Earth and our entire galaxy toward the unknown.
01:20The galaxy's traveling through space.
01:21Where is it going?
01:22It's an area of really cosmic mystery.
01:26So strap in for Earth's Cosmic Journey.
01:48We are Earth's passengers as our home planet travels through the cosmos.
01:57To us, everything seems calm.
02:02Nothing could be further from the truth.
02:05Contrary to what you might think just based on your everyday experience, the Earth is
02:09actually hurtling through space at amazing speeds in a lot of different ways.
02:15Even just the motion of the stars through the sky at night gives you a clue that the
02:19Earth is not sitting still.
02:23The Earth is spinning at every moment, and we can see this most clearly in the fact that
02:28we have day and night.
02:31We might not think about it, but our lives are tuned to Earth's journey as it spins through
02:41space.
02:43There's really nothing more basic to us than that cycle of day and night, that 24-hour
02:46cycle.
02:49All of life on Earth evolved with a day-night cycle, so it's ingrained into every organism
02:56on this planet.
03:00Life evolved in lockstep with Earth's spinning motion.
03:08But in the ocean, corals take things a step further by keeping a record of every planetary
03:19turn.
03:20They have a daily cycle which creates a deposit almost like a tree ring, but instead of it
03:27being once a year, it's once a day.
03:30So you look at a bunch of tree rings, you can count the number of years the tree was
03:33alive.
03:37Corals record not just the yearly cycle, but the daily cycle of night and day.
03:41These are recorded in these little growth bands in the coral.
03:45By counting the coral's growth bands, we can work out the number of days in a year.
03:52But when we look at ancient fossilized coral, we discover something strange.
03:59We can look at fossils of corals that are hundreds of millions of years old, and if
04:02we do that, we find that the year is not 365 days long, it's more like 420 days long.
04:13The length of a year is how long Earth takes to orbit the sun.
04:20Hundreds of millions of years ago, it took our planet the same amount of time to orbit
04:25as today.
04:28But somehow, there were 420 days.
04:35How is this possible?
04:41We all know that the rate of the spin of the Earth today is 24 hours, but it hasn't always
04:45been that way.
04:49When the ancient corals were alive, there were 420 days in one Earth year, meaning a
04:57day was just 21 hours long.
05:03To find out how this was possible, we need to go back to the start of Earth's cosmic
05:09journey.
05:164.6 billion years ago, our planet traveled a dangerous path through a chaotic and violent
05:26solar system.
05:32Collisions were frequent.
05:41One giant impact set our planet spinning rapidly.
05:56And formed the moon.
06:03Going all the way back to the time that the moon formed, the Earth may have had a day
06:08as short as two and a half hours.
06:12As the Earth continued on its path through the early solar system, our planet cooled
06:20and the surface became solid.
06:25The violence wasn't over.
06:29The young Earth was bombarded in the early days of the solar system.
06:34And when these rocks hit the Earth, they almost never hit directly on, they'd hit at an angle.
06:42With each collision, it adds a little bit more momentum and a little bit more spin to
06:55the Earth.
07:00The added spin that you get is kind of like a merry-go-round.
07:03You can imagine with each kid that pushes and jumps on the merry-go-round, you have
07:07greater spin.
07:12As our planet journeyed on, asteroid impacts set the young Earth spinning 12 times faster
07:19than it does today.
07:22Our planet's rotational speed has huge consequences for life.
07:28On Earth, the spin of our planet actually has an effect on our weather.
07:34With a shorter day, one of the effects that might have been apparent on Earth at that
07:39time was more storms developing.
07:43A phenomena still in action today drove these powerful ancient storms.
07:53We call it the Coriolis effect.
07:56The Earth's spin creates phenomena in Earth's atmosphere and oceans.
08:01This determines patterns of circulation in combination with the heat energy from the sun.
08:09The rotation of the Earth matched with solar heating, especially at the equator, causes
08:14air to rise up and then also sort of to move sideways and sets up spin.
08:19As the young Earth continued its journey, the planet's rotation whipped up furious,
08:26planet-wide storms.
08:30A fast spin would have been disastrous for any life.
08:36The storms would have been so big, it's hard to say if life would have evolved at all.
08:44Fortunately for humankind, Earth has a traveling companion, the moon, and it helps slow our
08:51planet's spin.
08:55What happened next was kind of a wonderful gravitational dance between these two bodies.
09:00As they were spinning, they were also interacting with each other.
09:04The moon's gravity pulled on Earth's oceans, generating tidal bulges.
09:11Material was moving in and out of the tidal bulges as they spun, and this creates friction
09:15and a kind of drag that actually slowed down the rotation.
09:22The tides also helped create life.
09:27Earth's tides swept nutrients from the land into the oceans for the first time.
09:34A primordial soup began brewing, and life arose.
09:49As Earth's spin continued to slow down, life spread across the planet.
09:58But our planet's spin is just one part of our cosmic ride.
10:08Realizing how complicated our larger environment in the universe is is a wonderful thing.
10:13There are so many things that affect the orbit of the Earth, the tilt of the Earth, things
10:17that affect our climate.
10:20Clues to the Earth's space voyage are hidden right across the world.
10:26Let our planet's wild ride explain how one of the driest places on the planet was once wet.
10:46The Sahara Desert. Dry, dusty, and desolate.
10:53But hidden deep in a desert cave is a clue that thousands of years ago, the Sahara was
11:01a lush, green paradise.
11:06Archaeologists have unearthed rock art which clearly depicts humans and animals swimming
11:12in lakes.
11:15And by looking at satellite images, we can trace out the outlines of ancient river valleys.
11:23The Earth's fast rotation influenced our planet's ancient weather patterns.
11:30Could another motion have changed the desert climate?
11:35To unravel the mystery, we need to rewind the clock 4.6 billion years.
11:45To when the infant solar system was a planetary shooting gallery.
11:54And the Earth, spanned through the solar system with a slight tilt.
12:03Earlier on, before the formation of the Moon, the Earth didn't have much of a tilt.
12:07And the impact knocked us completely out of whack to about 80 degrees.
12:15Our planet might have continued its journey tilted right over, but the Moon's gravity
12:24pulled us upright. Just not completely.
12:29The Moon is not quite in the equatorial plane of the Earth. It's above the equatorial plane
12:35and it pulls the Earth's axis into a 23.5 degree tilt.
12:42If we didn't have the tilt to about 23 degrees, then we wouldn't have the seasons.
12:46And these seasons drive a lot of the crops and the growth and the ability to survive
12:51all across the globe.
12:55But the ancient greening of the Sahara can't be explained by the changing seasons.
13:01Another planetary motion must be in play.
13:06A clue is found in the sky. The North Star.
13:13Right now, the Earth's axis is pointed towards a star in the sky called the North Star, Polaris.
13:20We've actually named it after the fact that the North Pole of the Earth points toward
13:24it in the sky.
13:26But Polaris hasn't always been the North Star.
13:31Five thousand years ago, it was a totally different star. It was Thuban, which is in
13:34Draco, a different constellation.
13:36Some time in the future, it'll be Vega, the brightest star in the constellation Lyra.
13:41So the North Star actually changes because the North Pole's position in the sky changes.
13:47The changing pole star is evidence that Earth is wobbling through space. It's a process
13:54called precession, something that also affects spinning tops.
14:00If you take a top and let it spin really rapidly and poke it, the axis of rotation
14:05will spin around like this. And it's much slower than the actual spin of the object.
14:10That is precession, this circle that the axis is making. This happens to the Earth as well.
14:20A cosmic poke caused Earth's space wobble. But what has the power to poke a planet?
14:31Once again, gravity is the key. This time, Earth's gravitational interactions with the
14:37Moon and Sun.
14:41These forces are that poke on the spinning Earth, and that's what makes the Earth's axis
14:46spin in precession. And it takes about 20,000 years to make a complete circle once.
14:52As the Earth continues its journey around the Sun, this wobbling motion changes the
14:58planet's climate dramatically. When the Earth's North Pole leans toward the Sun, Northern
15:05Hemisphere summers are sunnier, with unexpected consequences for the Sahara.
15:17It turns out at times when the climate in the Sahara gets more sunshine, that warms
15:24the climate up, and the winds come in from the ocean. It's called the monsoon effect,
15:29and brings water, rain, into the Sahara, where now it's dry.
15:37This pattern of wet and dry climates that produce this 20,000 year cycle is what we
15:43see in the Sahara, where at times of strong monsoon, the Sahara is wetter, a green Sahara.
15:5110,000 years ago, as the Earth wobbled through space, monsoons were unleashed, turning the
16:00desert green. Humans migrated to the newly lush Sahara, and created the cave paintings
16:08we see today. But this wasn't the first time humans crossed a green Sahara.
16:16A dry Sahara would have presented an insurmountable barrier to our ancestors from migrating out
16:26of Africa. But during one of these cycles, when the Sahara was green, it would have been
16:33a corridor that we could have migrated and dispersed on.
16:38This wobbling motion through space transformed the Sahara, and the fate of humankind. But
16:46there are more cosmic forces affecting our journey through the universe.
16:52The Earth's orbit around the sun is another thing that seems very, very solid. We understand
16:56how it works. But everything in the universe is a delicately tuned dance of gravity, and
17:02things can change even from tiny little influences.
17:06As our planet hurtles through space, other worlds influence our path.
17:19Earth carries us on a wild journey through the cosmos. And clues to the effects of this
17:27trip are hiding in our own backyard.
17:37In New York City, amongst the buildings and traffic, we find moraines, rocks left behind
17:50by retreating glaciers.
17:5318,000 years ago, a sheet of ice taller than any skyscraper covered Manhattan. Ice ages
18:00have struck regularly throughout Earth's history, putting our planet in a deep freeze.
18:12There was a period in Earth's history several hundred million years ago, the Snowball Earth
18:17period. We went through a very extreme glaciation, if you will, a very extreme ice age, where
18:22we think perhaps the entire Earth was covered in an ice sheet.
18:28The trigger. Earth's orbital dance around the sun.
18:37We tend to think of ourselves sitting relatively stationary on the Earth. It's pretty comforting,
18:41actually. But we're orbiting the sun at about 66,000 miles per hour.
18:47Every day, Earth travels over 1.6 million miles on its journey around the sun.
18:55This orbit isn't always completely round.
19:02Earth is generally going around the sun in more or less a circular orbit. But over time,
19:08the massaging of this orbit from the sun, from the moon, on the Earth's orbit causes
19:14the orbit of the Earth to change, so that sometimes it's an ellipse, sometimes it's
19:19Right now on the Earth, we're in kind of the most circular time in the orbit.
19:24So that means the summers are relatively mild and the winters are relatively mild.
19:29But imagine not that long ago in the past, it could have been really dramatically different.
19:34When the Earth is a little bit closer to the sun, maybe you have a really severe summer,
19:39and then on the other side of the orbit, you're a little farther away from the sun.
19:44Maybe you have a really severe summer, and then on the other side of the orbit,
19:49you're a little farther away from the sun than normal, so you have a really severe winter.
19:54Our environment is very, very sensitive to these things.
19:59And when the Earth's orbit is stretched out, that can actually trigger an ice age.
20:05Our planet's 100,000-year orbital cycle caused the ice age that buried New York.
20:11And ice ages have had a big impact on human history.
20:1615,000 years ago, plunging temperatures locked water away in glaciers and ice caps.
20:23Sea levels dropped, creating land bridges between continents.
20:29Humans migrated from Asia to America by foot.
20:35America was inhabited for the first time.
20:40May 2018, scientists revealed a whole new dynamic to Earth's journey.
20:47Every 405,000 years, our planet's orbital voyage stretches to the extreme,
20:54and Earth's planetary orbit is changing.
20:59Every 405,000 years, our planet's orbital voyage stretches to the extreme,
21:04and Earth's planetary neighbors are to blame.
21:09Because Jupiter is the most massive planet in our solar system,
21:13it is in many ways the bully on the playground, right?
21:16Its dynamics, its gravity, sculpts a lot of the dynamics of the solar system.
21:23It actually tugs and pulls on the orbit of the Earth itself.
21:27And it's responsible for some of the very changes that drive our climatic cycle here on our planet.
21:35Jupiter isn't the only bully in the playground.
21:40Venus is a fairly big planet about the size of the Earth and also comes closest to us in its orbit.
21:46So these two planets put just a little tiny elongation onto our Earth's orbit.
21:51And as this cycle continues, the more extreme it gets, we can actually notice a temperature difference
21:56about once every 405,000 years.
22:02Jupiter and Venus gang up on the Earth gravitationally, pulling Earth's orbit into an even greater ellipse.
22:11Our planet's hot weather becomes hotter, and its cold weather gets much colder.
22:22Today, we're in a moderate part of the cycle.
22:25But in just 60,000 years' time, we could plunge into another deep freeze.
22:33It's a little bit like a cosmic butterfly effect.
22:35I mean, even the smallest effects can have, you know, big influence over time.
22:43Earth's orbit around the sun is just part of our far larger cosmic journey.
22:51The entire solar system is hurtling around the Milky Way, taking us places we don't want to be.
23:02Sometimes our planet might wander into what's essentially a bad neighborhood.
23:08Could these neighborhoods spell disaster for life on Earth?
23:22Over the last 3.7 billion years, a series of extinction events wiped out almost 95% of all species on Earth.
23:41Now, research suggests our planet's orbit could be partly to blame.
23:48Not Earth's voyage around the sun.
23:51Our planet's larger and longer journey around the Milky Way.
23:57Our solar system and our sun is shooting through the galaxy at about 537,000 miles per hour around the center of our galaxy.
24:06And that center of the galaxy is about 26,000 light years away.
24:09So it should take the sun about 230 million years to trace out one full orbit around the center of the galaxy.
24:17Despite racing around the Milky Way at half a million miles an hour,
24:23Earth has completed less than 20 laps of the galaxy in our planet's entire history.
24:30And it turns out this galactic ride is more complex than it seems.
24:37Now, if you look at the Earth going around the sun, it defines an ellipse, but that's a flat figure.
24:43And you think, well, the sun probably goes around in a plane as well.
24:47And it turns out, not that simple.
24:52Most of the mass of the solar system is concentrated in the sun.
24:56So Earth and the other planets smoothly orbit our star.
25:02The mass of the Milky Way is spread out unevenly.
25:07That changes the gravity of the galaxy, and so it changes how things move in it.
25:13And in fact, if you give something a little bit of an up or down motion, it'll bob up and down as it goes around.
25:20Riding the Earth is almost like riding a carousel.
25:23As the sun and the Earth go around the galaxy, the sun also goes up and down,
25:28like you're on one of those horses with the pole.
25:31And so what this can do is take us into different galactic environments.
25:39This bobbing motion takes Earth and the solar system on a 60,000-year journey up and down through the Milky Way's galactic plane.
25:50Our orbit also takes us through different galactic neighborhoods.
25:59Today, we're traveling through a calm suburb of the galaxy.
26:05But sometimes things get a little bumpy.
26:09Sometimes our sun and our planet might wander into what's essentially a bad neighborhood.
26:16You know, maybe it's an area where there's a lot of star formation going on, where there's a lot of young stars that are very active.
26:22Or maybe it's a location where there are dying stars and things are about to get really hot.
26:28The baddest neighborhoods in the galaxy may be the spiral arms.
26:36These gas-filled regions orbit the galactic center more slowly than the Earth.
26:43So our planet passes through an arm roughly every 150 million years.
26:49These arms are where gas clouds tend to hang out.
26:53And if they get compressed, they form a lot of stars.
26:57When they form a lot of stars, they make bright blue stars.
27:02And they don't last long, and they blow up as supernovae.
27:07So it's possible that as we're passing through these regions, these are places you might not want to be in.
27:13So in the distant past, this may have affected the Earth.
27:22When giant stars go supernova, the star's outer layers blast into space.
27:29Along with a shockwave traveling at 25,000 miles per second, supernovae also release cosmic rays.
27:40Space bullets that shoot across the galaxy at close to the speed of light.
27:46And you don't want to be exposed to too many of them.
27:50But in high enough doses, these things penetrate our cells and damage our DNA.
27:54And over the long term, can cause really bad damage to human bodies.
28:00As we ride through space, Earth's magnetic field protects us from most of the radiation.
28:06And it's a good thing.
28:10But in 2018, we discovered evidence that a hail of space bullets overwhelmed our planet's magnetic field in the past.
28:18In many ways, we really take for granted how the Earth protects us from space.
28:24But there are records that we've actually bounced a little too close to exploding stars.
28:30Sediments in the ocean show that about two million years ago, iron-60 was deposited in our oceans.
28:36Iron-60 is a radioactive isotope of iron.
28:39And there's only one way we know of it being made in the universe, and that is exploding stars.
28:49Around the same time, the Earth's magnetic field is getting stronger and stronger.
28:55And we're getting closer and closer to exploding stars.
28:59Around 2.8 million years ago, a supernova exploded just 150 light-years from Earth.
29:09A few hundred years later, a blizzard of cosmic rays slammed into the Earth, tearing through our magnetic field.
29:18These space bullets are a prime suspect in the extinction of over a third of all coastal marine species.
29:29Now, this is not necessarily tied to the Earth passing through one of these spiral arms.
29:35But it shows you that being close to a supernova is not necessarily a thing you want to do.
29:42Millions of years in the future, Earth will pass through another spiral arm as our planet continues its journey through the Milky Way.
29:54And we will wander into harm's way once again.
30:00But supernovas aren't the only cosmic threat linked to Earth's journey through the galaxy.
30:0766 million years ago, a trillion-ton object hit the Earth at 25,000 miles an hour, blowing 5 trillion tons of debris into the sky.
30:24This impact wiped out the dinosaurs.
30:32And this extinction event wasn't a one-off.
30:38If one looks at the geological record, let's say one looks at the record of life,
30:43it turns out that mass extinctions of life, like the dinosaur mass extinction, didn't happen just once.
30:50They happen about every 26 or so million years.
30:54That's essentially the same cycle.
30:58A controversial theory suggests our galactic orbit is to blame.
31:07When the Earth is bobbing through the galactic plane, we run the risk of passing close to other stars.
31:15These stars can gravitationally disrupt the solar system around us,
31:22including the Oort Cloud, a shell of 2 trillion icy bodies loosely bound to the solar system.
31:31One thing that can happen is comets can be sent into the inner solar system, increasing the rate of collisions.
31:45If the comet is big enough, it can cause a mass extinction like the one that happened 66 million years ago.
31:55The death of the dinosaur, along with 70% of all life on Earth, lines up with our passage through the galactic plane.
32:05The event killed off the masters of the planet, but allowed the rise of a new creature, mammals, and ultimately us.
32:22But there's another part of our journey through space that remains a mystery.
32:28The Earth is spinning like a top on its axis.
32:31It's orbiting around the sun.
32:33The sun itself is orbiting around the center of the Milky Way, but that's far from it.
32:40The Milky Way is speeding through the universe, and we are being dragged along for the ride.
32:47The problem is, we can't see where we're going.
32:51Could Earth be headed for a galactic crash?
33:02Like the craziest theme park ride, we are riding the Earth on a wild journey through the cosmos.
33:16Our planet spins, tilts, and wobbles around the solar system, while bobbing like a carousel through the Milky Way.
33:32The dynamics of the Earth moving in the cosmic void is like the most unbelievable journey you could ever imagine.
33:40And as you get to larger scales, the motions only become grander and larger and more dynamic.
33:49In 1977, we tried to work out the largest motion of all.
33:56The movement of our galaxy through the universe.
34:00Clues hide in the Cosmic Microwave Background, a remnant from the birth of the universe.
34:07The Cosmic Microwave Background is the radiation that's left over from the hot Big Bang.
34:13The Cosmic Microwave Background is shining in all directions. It's sort of this fixed thing.
34:18And if we're moving through it with some speed, we will see that in the light itself.
34:22You can measure that, and by measuring that you can get a sense of how fast we're moving through that space.
34:29By tracking our movement through the universe against a fixed point, we can work out the Milky Way's speed and direction.
34:39But in 1977, telescopes weren't the best tools for the job.
34:46During the Cold War, 1977, you have the newly declassified U-2 spy plane, this very high altitude reconnaissance aircraft.
34:53NASA retrofitted one of them with an upward facing window, and with very sensitive receivers,
34:59this spy plane became the first experiment to, for the first time, definitively measure the motion of the galaxy through the universe.
35:08As the U-2 spy plane soared above the Earth, it measured the Cosmic Microwave Background in unprecedented detail.
35:17The data revealed that our galaxy races through the universe at 370 miles a second.
35:28That's over a million miles an hour.
35:34Think of how big a galaxy is. Hundreds of millions of stars, and we're moving at hundreds of miles per second.
35:42That's just a tiny bit mind-blowing.
35:46The Milky Way's speed is the most alarming part of our galactic journey.
35:53From Earth, we can't see in the direction our galaxy is taking us.
35:59We're flying blind, our view blocked by the Milky Way itself.
36:04So if you are actually looking through the plane of the galaxy, through the plane of the pancake,
36:09your view of the galaxy is obscured by curtains of dust and gas that envelop our solar system.
36:16It's very bright, there's a lot of stars, and our view is blocked by the galaxy itself.
36:21So there's a zone directly behind the galaxy as we look towards the galactic center that's really an unknown area.
36:28It's a zone we call the zone of avoidance, and it's an area of really cosmic mystery.
36:34Thanks to this mysterious zone, we thought we could be headed for a galactic car crash.
36:48Then we had a breakthrough.
36:51We used powerful radio telescopes to look through the zone of avoidance for the first time.
37:04One of the nice things about using light that's in the radio is that this kind of light actually can go through the radio.
37:11It can go through the radio.
37:14One of the nice things about using light that's in the radio is that this kind of light actually can go through
37:21pretty dense kinds of gas and stars and allows us to sort of look through things.
37:26Using these radio telescopes has given us a glimpse into what lies beyond the zone of avoidance.
37:33Peering through the cloud of cosmic gas, we discovered that our galaxy
37:40is just one tiny element in a vast cluster of galaxies
37:47sailing through the cosmos together.
37:51We think that our galaxy, the Milky Way, is part of a much grander cosmic flow of galaxies.
37:57And it is part of what may be the Laniakea supercluster of galaxies,
38:01this giant, giant cosmic structure filled with potentially thousands of galaxies
38:05that is moving together in this beautiful, like, slow-moving river
38:10that is sculpted and dictated by gravity itself.
38:15Earth voyages through space along gravitational rivers hundreds of millions of light years long,
38:23along with a fleet of 100,000 other galaxies,
38:28all moving toward a single point in space,
38:31a gravitational drain known as the Great Attractor.
38:37The Great Attractor is the local region of gravity, of strong gravity,
38:44in this patch of the universe.
38:47It's where all the galaxies in this chunk of the universe are flowing towards.
38:52At the location of the Great Attractor is a bunch of material,
38:56a bunch of gas, a bunch of galaxies, an extremely massive cluster.
39:01And over time, more and more galaxies add themselves to this cluster
39:08as they continue to join the Great Attractor.
39:12It's unlikely Earth will ever reach the Great Attractor.
39:17As we speed towards it, we are heading for a collision after all.
39:23Is this how our cosmic journey ends?
39:32A clue comes from the Milky Way's traveling companion, another galaxy, Andromeda,
39:40filled with up to a trillion stars that's charting a similar path to us.
39:46The Andromeda Galaxy is another big spiral galaxy, a lot like our Milky Way,
39:52and it turns out the two of us are heading for each other.
39:57Andromeda and the Milky Way are currently 2.5 million light years apart,
40:04but hurtling towards each other at over 250,000 miles per hour,
40:09a collision is inevitable.
40:13Galaxies colliding with each other sounds like science fiction,
40:17but the collision of the Andromeda Galaxy and the Milky Way Galaxy will be a spectacular event.
40:23When the Andromeda and Milky Way Galaxies collide, it's going to be a ridiculous light show.
40:29The stars don't collide, but the giant clouds of gas do.
40:33And that's going to trigger star formation, so we're going to have what's known as a starburst galaxy.
40:40When Andromeda finally merges with the Milky Way, all bets are off.
40:45All of a sudden the system of hundreds of billions of stars will be added to our own, and there will be mass chaos.
40:52But one thing you can guarantee, there is going to be celestial fireworks.
40:56This could be the biggest light show in history, resulting in the creation of a brand new galaxy.
41:04We will have become one giant galaxy. Call it Milkdromeda, if you will.
41:10So we will look very different. Our grand design spiral Milky Way Galaxy will have probably become a giant galaxy.
41:18The merging galaxies could create a giant elliptical shaped galaxy.
41:23But Earth might not be around to see it.
41:27Billions of stars are going to come careening into our galaxy, very, very easily disrupting the orbit of the Earth.
41:34And that's going to be a huge event.
41:37And that's going to be a huge event.
41:40And that's going to be a huge event.
41:42Billions of stars are going to come careening into our galaxy, very, very easily disrupting the orbit of the Earth.
41:49The sun could be thrown out of the galaxy entirely.
41:56As stars, dust and gas swirl around each other,
42:02gravitational interactions could slingshot our solar system out into intergalactic space.
42:13We'll still orbit the sun and everything will be fine, kind of.
42:17But it just means we'll see something very different in our sky in 4.6 billion years than we do now.
42:25Our planet could be sent on a whole new intergalactic ride.
42:31Shot out into the cosmos, away from the new Milkdromeda galaxy.
42:38There's no way of knowing exactly what's going to happen.
42:42In that sense, journeys end?
42:48We'll just have to wait and see.
42:58We might not know the final destination for Earth's cosmic journey,
43:04but what an incredible ride it's been so far.
43:09We've had a fantastic journey over the history of Earth's existence.
43:14We may not be immediately aware of our motions through the universe, but that doesn't mean they're not there.
43:23Many people think of the Earth as this blue calm marble in space.
43:29But in reality, it's violently ripping around the sun and the sun is ripping about the galaxy.
43:36There's a lot of dynamics happening.
43:41It boggles the mind just to think of what the Earth will have done.
43:47The Earth would have actually orbited the sun 10 billion times.
43:52It would have spun on its axis like a trillion times and the galaxy is moving through space.
44:01Riding the Earth is anything but a boring trip.
44:05NASA Jet Propulsion Laboratory, California Institute of Technology