1 00:00:00,701 --> 00:00:04,336 ♪ 2 00:00:04,338 --> 00:00:08,941 narrator: The earth is taking us on the ride of our lives, 3 00:00:08,943 --> 00:00:13,112 hurtling through space in ways we never imagined. 4 00:00:13,114 --> 00:00:15,314 The earth is extremely dynamic. 5 00:00:15,316 --> 00:00:17,483 It is spinning on its axis. 6 00:00:17,485 --> 00:00:19,251 It's whirling about the sun. 7 00:00:19,253 --> 00:00:22,187 It's corkscrewing throughout this galaxy. 8 00:00:22,189 --> 00:00:24,623 It's just never a dull moment. 9 00:00:24,625 --> 00:00:27,026 It's like doing a waltz on top of a carousel 10 00:00:27,028 --> 00:00:29,795 that's on top of a high-speed train. 11 00:00:29,797 --> 00:00:32,564 Narrator: Now we're unlocking the secrets 12 00:00:32,566 --> 00:00:37,202 of our planet's voyage and discovering that earth's journey 13 00:00:37,204 --> 00:00:38,670 affects us all. 14 00:00:38,672 --> 00:00:41,240 ♪ 15 00:00:41,242 --> 00:00:44,343 we see evidence of this motion everywhere we look, 16 00:00:44,345 --> 00:00:47,713 not just in the motions of objects in the sky, 17 00:00:47,715 --> 00:00:51,116 but in the land and the seas themselves. 18 00:00:51,118 --> 00:00:53,118 Life on earth wouldn't be the same 19 00:00:53,120 --> 00:00:54,420 if we didn't find ourselves 20 00:00:54,422 --> 00:00:56,722 in this dramatic environment in space. 21 00:00:56,724 --> 00:00:59,224 ♪ 22 00:00:59,226 --> 00:01:01,527 narrator: But the ride can be dangerous... 23 00:01:01,529 --> 00:01:02,928 ♪ 24 00:01:02,930 --> 00:01:05,064 [ explosion ] 25 00:01:05,066 --> 00:01:07,800 plunging our planet into the deep freeze... 26 00:01:07,802 --> 00:01:09,301 [ ice cracking ] 27 00:01:10,571 --> 00:01:13,205 putting us in the path of supernovas, 28 00:01:13,207 --> 00:01:15,607 ♪ 29 00:01:15,609 --> 00:01:20,379 pulling earth and the entire galaxy toward the unknown. 30 00:01:20,381 --> 00:01:21,880 The galaxy is traveling through space. 31 00:01:21,882 --> 00:01:23,949 Where is it going? 32 00:01:23,951 --> 00:01:26,552 It's an area of really cosmic mystery. 33 00:01:26,554 --> 00:01:30,889 Narrator: So strap in for earth's cosmic journey. 34 00:01:30,891 --> 00:01:33,759 [ electricity crackles ] 35 00:01:33,761 --> 00:01:36,762 [ explosion ] 36 00:01:36,764 --> 00:01:39,765 -- captions by vitac -- www.Vitac.Com 37 00:01:39,767 --> 00:01:42,768 captions paid for by discovery communications 38 00:01:42,770 --> 00:01:48,907 ♪ 39 00:01:48,909 --> 00:01:53,378 we are earth's passengers as our home planet 40 00:01:53,380 --> 00:01:55,314 travels through the cosmos. 41 00:01:55,316 --> 00:01:57,850 ♪ 42 00:01:57,852 --> 00:02:02,554 to us, everything seems calm. 43 00:02:02,556 --> 00:02:05,958 Nothing could be further from the truth. 44 00:02:05,960 --> 00:02:07,226 Contrary to what you might think 45 00:02:07,228 --> 00:02:09,061 just based on your everyday experience, 46 00:02:09,063 --> 00:02:11,230 the earth is actually hurtling through space 47 00:02:11,232 --> 00:02:13,732 at amazing speeds in a lot of different ways. 48 00:02:13,734 --> 00:02:15,901 [ crickets chirping ] 49 00:02:15,903 --> 00:02:18,470 even just the motion of the stars through the sky at night 50 00:02:18,472 --> 00:02:21,273 gives you a clue that the earth is not sitting still. 51 00:02:21,275 --> 00:02:23,342 ♪ 52 00:02:23,344 --> 00:02:26,145 the earth is spinning at every moment, 53 00:02:26,147 --> 00:02:28,313 and we can see this most clearly in the fact 54 00:02:28,315 --> 00:02:31,116 that we have day and night. 55 00:02:31,118 --> 00:02:33,452 Narrator: We might not think about it, 56 00:02:33,454 --> 00:02:35,187 but our lives are tuned 57 00:02:35,189 --> 00:02:39,291 to earth's journey as it spins through space. 58 00:02:39,293 --> 00:02:43,128 ♪ 59 00:02:43,130 --> 00:02:44,596 there's really nothing more basic to us 60 00:02:44,598 --> 00:02:49,601 than that cycle of day and night, that 24-hour cycle. 61 00:02:49,603 --> 00:02:53,438 All of life on earth evolved with the day-night cycle, 62 00:02:53,440 --> 00:02:57,809 so it's ingrained into every organism on this planet. 63 00:02:57,811 --> 00:03:01,146 ♪ 64 00:03:01,148 --> 00:03:02,915 narrator: Life evolved in lockstep 65 00:03:02,917 --> 00:03:05,117 with earth's spinning motion. 66 00:03:05,119 --> 00:03:08,754 ♪ 67 00:03:08,756 --> 00:03:12,658 but in the ocean, corals take things a step further 68 00:03:12,660 --> 00:03:16,929 ♪ 69 00:03:16,931 --> 00:03:20,799 by keeping a record of every planetary turn. 70 00:03:20,801 --> 00:03:22,968 ♪ 71 00:03:22,970 --> 00:03:25,304 they have a daily cycle, which creates a deposit 72 00:03:25,306 --> 00:03:26,705 almost like a tree ring, 73 00:03:26,707 --> 00:03:30,475 but instead of it being once a year, it's once a day. 74 00:03:30,477 --> 00:03:31,910 So, you look a bunch of tree rings, 75 00:03:31,912 --> 00:03:35,147 you can count the number of years the tree was alive. 76 00:03:35,149 --> 00:03:37,449 ♪ 77 00:03:37,451 --> 00:03:39,451 corals record not just the yearly cycle, 78 00:03:39,453 --> 00:03:41,687 but the daily cycle of night and day. 79 00:03:41,689 --> 00:03:43,755 These are recorded in these little growth bands 80 00:03:43,757 --> 00:03:45,591 in the coral. 81 00:03:45,593 --> 00:03:47,826 Narrator: By counting the corals' growth bands, 82 00:03:47,828 --> 00:03:52,197 we can work out the number of days in a year. 83 00:03:52,199 --> 00:03:57,035 Sounds simple, but when we look at ancient, fossilized coral, 84 00:03:57,037 --> 00:03:59,571 we discover something strange. 85 00:03:59,573 --> 00:04:01,139 We can look at fossils of corals 86 00:04:01,141 --> 00:04:02,908 that are hundreds of millions of years old, 87 00:04:02,910 --> 00:04:08,213 and if we do that, we find that the year is not 365 days long. 88 00:04:08,215 --> 00:04:11,783 It's more like 420 days long. 89 00:04:11,785 --> 00:04:14,853 ♪ 90 00:04:14,855 --> 00:04:16,955 narrator: When the ancient corals were alive, 91 00:04:16,957 --> 00:04:20,659 there were 420 days in one earth year, 92 00:04:20,661 --> 00:04:23,228 ♪ 93 00:04:23,230 --> 00:04:26,632 meaning a day was just 21 hours long. 94 00:04:26,634 --> 00:04:29,368 ♪ 95 00:04:29,370 --> 00:04:31,336 to find out how this was possible, 96 00:04:31,338 --> 00:04:35,607 we need to go back to the start of earth's cosmic journey. 97 00:04:35,609 --> 00:04:41,980 ♪ 98 00:04:41,982 --> 00:04:46,084 4.6 billion years ago, 99 00:04:46,086 --> 00:04:49,721 our planet traveled a dangerous path 100 00:04:49,723 --> 00:04:52,457 through a chaotic and violent solar system. 101 00:04:52,459 --> 00:04:55,961 ♪ 102 00:04:55,963 --> 00:04:57,696 [ explosion ] 103 00:04:57,698 --> 00:04:59,665 collisions were frequent. 104 00:04:59,667 --> 00:05:06,438 ♪ 105 00:05:06,440 --> 00:05:11,410 one giant impact set our planet spinning rapidly... 106 00:05:11,412 --> 00:05:14,246 [ explosion ] 107 00:05:14,248 --> 00:05:19,618 ♪ 108 00:05:19,620 --> 00:05:24,956 ♪ 109 00:05:24,958 --> 00:05:26,858 and formed the moon. 110 00:05:28,796 --> 00:05:32,297 Going all the way back to the time that the moon formed, 111 00:05:32,299 --> 00:05:36,068 the earth may have had a day as short as 2 1/2 hours. 112 00:05:36,070 --> 00:05:38,470 ♪ 113 00:05:38,472 --> 00:05:40,539 narrator: As the earth continued on its path 114 00:05:40,541 --> 00:05:44,443 through the early solar system, 115 00:05:44,445 --> 00:05:48,313 our planet cooled, and the surface became solid. 116 00:05:48,315 --> 00:05:50,882 ♪ 117 00:05:50,884 --> 00:05:54,786 but the violence wasn't over. 118 00:05:54,788 --> 00:05:58,190 The young earth was bombarded 119 00:05:58,192 --> 00:06:00,325 in the early days of the solar system, 120 00:06:00,327 --> 00:06:02,828 and when these rocks hit the earth, 121 00:06:02,830 --> 00:06:04,963 they almost never hit directly on. 122 00:06:04,965 --> 00:06:07,099 They'd hit at an angle. 123 00:06:07,101 --> 00:06:17,008 ♪ 124 00:06:17,010 --> 00:06:20,245 with each collision, it adds a little bit more momentum 125 00:06:20,247 --> 00:06:22,414 and a little bit more spin to the earth. 126 00:06:26,286 --> 00:06:29,554 The added spin that you get is a kind of like a merry-go-round. 127 00:06:29,556 --> 00:06:31,990 You can imagine with each kid that pushes and jumps 128 00:06:31,992 --> 00:06:34,760 on the merry-go-round, you have greater spin. 129 00:06:38,132 --> 00:06:41,466 Narrator: As our planet journeyed on, asteroid impacts 130 00:06:41,468 --> 00:06:42,901 set the young earth 131 00:06:42,903 --> 00:06:46,571 spinning 12 times faster than it does today. 132 00:06:48,542 --> 00:06:54,312 Our planet's rotational speed has huge consequences for life. 133 00:06:54,314 --> 00:06:56,882 On earth, the spin of our planet 134 00:06:56,884 --> 00:07:00,519 actually has an effect on our weather. 135 00:07:00,521 --> 00:07:02,454 With a shorter day, 136 00:07:02,456 --> 00:07:04,990 one of the effects that might have been apparent on earth 137 00:07:04,992 --> 00:07:08,960 at that time was more storms developing. 138 00:07:08,962 --> 00:07:11,296 [ thunder crashes ] 139 00:07:11,298 --> 00:07:13,765 narrator: A phenomenon still in action today 140 00:07:13,767 --> 00:07:16,701 drove these powerful ancient storms. 141 00:07:19,306 --> 00:07:22,574 We call it the coriolis effect. 142 00:07:22,576 --> 00:07:25,610 The earth's spin creates phenomena 143 00:07:25,612 --> 00:07:27,546 in earth's atmosphere and oceans. 144 00:07:27,548 --> 00:07:29,781 This determines patterns of circulation 145 00:07:29,783 --> 00:07:32,551 in combination with the heat energy from the sun. 146 00:07:32,553 --> 00:07:35,487 [ thunder crashes ] 147 00:07:35,489 --> 00:07:38,390 the rotation of the earth matched with solar heating, 148 00:07:38,392 --> 00:07:41,460 especially at the equator, causes air to rise up 149 00:07:41,462 --> 00:07:45,664 and then also sort of to move sideways and sets up spin. 150 00:07:45,666 --> 00:07:48,066 Narrator: As the young earth continued its journey, 151 00:07:48,068 --> 00:07:53,004 the planet's rotation whipped up ferocious, planet-wide storms. 152 00:07:56,844 --> 00:08:01,847 The fast spin would have been disastrous for any life. 153 00:08:01,849 --> 00:08:03,248 The storms would have been so big, 154 00:08:03,250 --> 00:08:07,152 it's hard to say if life would have evolved at all. 155 00:08:09,756 --> 00:08:11,790 Narrator: Fortunately for humankind, 156 00:08:11,792 --> 00:08:15,026 earth has a traveling companion -- 157 00:08:15,028 --> 00:08:19,364 the moon, and it helped slow our planet's spin. 158 00:08:21,568 --> 00:08:24,469 What happened next was kind of a wonderful gravitational dance 159 00:08:24,471 --> 00:08:26,304 between these two bodies. 160 00:08:26,306 --> 00:08:28,440 As they were spinning, they were also interacting 161 00:08:28,442 --> 00:08:30,075 with each other. 162 00:08:30,077 --> 00:08:33,345 Narrator: The moon's gravity pulled on earth's oceans, 163 00:08:33,347 --> 00:08:36,448 generating tidal bulges. 164 00:08:36,450 --> 00:08:39,951 Materials moving in and out of the tidal bulges as they spun, 165 00:08:39,953 --> 00:08:42,120 and this creates friction and a kind of drag 166 00:08:42,122 --> 00:08:44,089 that actually slowed down the rotation. 167 00:08:44,091 --> 00:08:48,059 ♪ 168 00:08:48,061 --> 00:08:51,429 narrator: The tides also helped create life. 169 00:08:51,431 --> 00:08:54,900 Giant tides swept nutrients from the land 170 00:08:54,902 --> 00:08:59,304 into the oceans for the first time. 171 00:08:59,306 --> 00:09:02,207 A primordial soup began brewing. 172 00:09:02,209 --> 00:09:05,110 ♪ 173 00:09:05,112 --> 00:09:07,279 and life arose. 174 00:09:07,281 --> 00:09:14,653 ♪ 175 00:09:14,655 --> 00:09:17,589 as earth's spin continued to slow down, 176 00:09:17,591 --> 00:09:20,592 ♪ 177 00:09:20,594 --> 00:09:23,261 life spread across the planet. 178 00:09:23,263 --> 00:09:28,733 ♪ 179 00:09:28,735 --> 00:09:33,872 but our planet's spin is just one part of our cosmic ride. 180 00:09:33,874 --> 00:09:36,975 Realizing how complicated our larger environment 181 00:09:36,977 --> 00:09:39,110 in the universe is is a wonderful thing. 182 00:09:39,112 --> 00:09:41,479 There's so many things that affect the orbit of the earth, 183 00:09:41,481 --> 00:09:44,349 the tilt of the earth, things that affect our climate. 184 00:09:44,351 --> 00:09:46,484 ♪ 185 00:09:46,486 --> 00:09:49,588 narrator: Clues to earth's space voyage are hidden 186 00:09:49,590 --> 00:09:52,857 all across the world. 187 00:09:52,859 --> 00:09:55,360 Could our planet's wild ride explain 188 00:09:55,362 --> 00:10:00,031 how one of the driest places on the planet was once wet? 189 00:10:00,033 --> 00:10:03,835 ♪ 190 00:10:05,372 --> 00:10:10,575 ♪ 191 00:10:10,577 --> 00:10:15,780 ♪ 192 00:10:15,782 --> 00:10:21,453 narrator: The sahara desert -- dry, dusty, desolate. 193 00:10:21,455 --> 00:10:23,521 ♪ 194 00:10:23,523 --> 00:10:26,558 but hidden deep in a desert cave 195 00:10:26,560 --> 00:10:30,095 is a clue that thousands of years ago, 196 00:10:30,097 --> 00:10:35,433 the sahara was a lush, green paradise. 197 00:10:35,435 --> 00:10:38,737 Archaeologists have unearthed rock art 198 00:10:38,739 --> 00:10:45,343 which clearly depicts humans and animals swimming in lakes, 199 00:10:45,345 --> 00:10:47,345 and by looking at satellite images, 200 00:10:47,347 --> 00:10:51,716 we can trace out the outlines of ancient river valleys. 201 00:10:51,718 --> 00:10:54,619 ♪ 202 00:10:54,621 --> 00:10:56,921 narrator: The earth's fast rotation influenced 203 00:10:56,923 --> 00:11:00,759 our planet's ancient weather patterns. 204 00:11:00,761 --> 00:11:05,163 Could another motion have changed the desert climate? 205 00:11:05,165 --> 00:11:08,199 To unravel the mystery, we need to rewind the clock 206 00:11:08,201 --> 00:11:10,735 4.6 billion years 207 00:11:10,737 --> 00:11:14,639 ♪ 208 00:11:14,641 --> 00:11:18,343 to when the infant solar system 209 00:11:18,345 --> 00:11:20,545 was a planetary shooting gallery 210 00:11:20,547 --> 00:11:27,218 ♪ 211 00:11:27,220 --> 00:11:32,857 and the earth spun through the solar system with a slight tilt. 212 00:11:32,859 --> 00:11:34,826 Earlier on, before the formation of the moon, 213 00:11:34,828 --> 00:11:36,895 the earth didn't have much of a tilt, 214 00:11:36,897 --> 00:11:39,164 and the impact knocked us completely out of whack 215 00:11:39,166 --> 00:11:40,999 to about 80 degrees. 216 00:11:41,001 --> 00:11:44,035 [ explosion ] 217 00:11:47,808 --> 00:11:50,642 narrator: Our planet might have continued its journey 218 00:11:50,644 --> 00:11:53,978 tilted right over, but over billions of years, 219 00:11:53,980 --> 00:11:57,048 the moon's gravity pulled the earth upright, 220 00:11:57,050 --> 00:11:59,084 just not completely. 221 00:11:59,086 --> 00:12:03,421 The moon is not quite in the equatorial plane of the earth. 222 00:12:03,423 --> 00:12:05,356 It's above the equatorial plane, 223 00:12:05,358 --> 00:12:12,263 and it pulls the earth's axis into a 23 1/2-degree tilt. 224 00:12:12,265 --> 00:12:14,799 Stricker: If we didn't have the tilt to about 23 degrees, 225 00:12:14,801 --> 00:12:16,301 then we wouldn't have the seasons, 226 00:12:16,303 --> 00:12:19,704 and these seasons drive a lot of the crops and the growth 227 00:12:19,706 --> 00:12:24,409 and the ability to survive all across the globe. 228 00:12:24,411 --> 00:12:26,945 Narrator: But the ancient greening of the sahara 229 00:12:26,947 --> 00:12:31,116 can't be explained by the changing seasons. 230 00:12:31,118 --> 00:12:35,587 Another planetary motion must be in play. 231 00:12:35,589 --> 00:12:40,058 A clue is found in the night sky -- 232 00:12:40,060 --> 00:12:43,261 the north star. 233 00:12:43,263 --> 00:12:47,198 Right now, the earth's axis is pointed towards a star 234 00:12:47,200 --> 00:12:50,368 in the sky called the north star -- polaris. 235 00:12:50,370 --> 00:12:52,437 We've actually named it after the fact 236 00:12:52,439 --> 00:12:56,107 that the north pole of the earth points toward it in the sky. 237 00:12:56,109 --> 00:13:00,712 Narrator: But polaris hasn't always been the north star. 238 00:13:00,714 --> 00:13:03,081 5,000 years ago, it was a totally different star. 239 00:13:03,083 --> 00:13:04,883 It was thuban, which is in draco, 240 00:13:04,885 --> 00:13:06,417 a different constellation. 241 00:13:06,419 --> 00:13:08,419 Sometime in the future, it'll be vega, 242 00:13:08,421 --> 00:13:10,755 the brightest star in the constellation lyra, 243 00:13:10,757 --> 00:13:12,590 so the north star actually changes 244 00:13:12,592 --> 00:13:16,995 because the north pole's position in the sky changes. 245 00:13:16,997 --> 00:13:19,597 Narrator: The changing pole star is evidence 246 00:13:19,599 --> 00:13:23,001 that earth is wobbling through space. 247 00:13:23,003 --> 00:13:26,171 It's a process called precession, 248 00:13:26,173 --> 00:13:29,707 something that also affects spinning tops. 249 00:13:29,709 --> 00:13:32,343 Plait: If you take a top and let it spin really rapidly 250 00:13:32,345 --> 00:13:33,711 and poke it, 251 00:13:33,713 --> 00:13:36,981 the axis of rotation will spin around like this, 252 00:13:36,983 --> 00:13:40,118 and it's much slower than the actual spin of the object. 253 00:13:40,120 --> 00:13:44,823 That is precession, this circle that the axis is making. 254 00:13:44,825 --> 00:13:46,991 This happens to the earth, as well. 255 00:13:46,993 --> 00:13:50,595 ♪ 256 00:13:50,597 --> 00:13:55,066 narrator: A cosmic poke caused earth's space wobble, 257 00:13:55,068 --> 00:13:57,602 but what has the power to poke a planet? 258 00:13:57,604 --> 00:14:00,905 ♪ 259 00:14:00,907 --> 00:14:04,242 once again, the key is gravity, 260 00:14:04,244 --> 00:14:07,312 this time earth's gravitational interactions 261 00:14:07,314 --> 00:14:10,949 with the moon and sun. 262 00:14:10,951 --> 00:14:14,419 These forces are that poke on the spinning earth, 263 00:14:14,421 --> 00:14:17,722 and that's what makes the earth's axis spin in precession, 264 00:14:17,724 --> 00:14:22,861 and it takes about 20,000 years to make a complete circle once. 265 00:14:22,863 --> 00:14:26,130 Narrator: As the earth continues its journey around the sun, 266 00:14:26,132 --> 00:14:29,934 this precession changes the planet's climate dramatically. 267 00:14:29,936 --> 00:14:33,271 When the earth's north pole leans toward the sun, 268 00:14:33,273 --> 00:14:35,907 northern hemisphere summers are sunnier... 269 00:14:35,909 --> 00:14:40,411 ♪ 270 00:14:40,413 --> 00:14:44,148 with unexpected consequences for the sahara. 271 00:14:44,150 --> 00:14:47,252 ♪ 272 00:14:47,254 --> 00:14:49,587 rampino: It turns out that at times when 273 00:14:49,589 --> 00:14:53,157 the climate in the sahara gets more sunshine, 274 00:14:53,159 --> 00:14:55,126 that warms the climate up, 275 00:14:55,128 --> 00:14:57,695 and the winds come in from the ocean. 276 00:14:57,697 --> 00:15:01,266 It's called the monsoon effect and brings water -- 277 00:15:01,268 --> 00:15:04,702 rain into the sahara, where now it's dry. 278 00:15:04,704 --> 00:15:07,305 ♪ 279 00:15:07,307 --> 00:15:10,575 olsen: This pattern of wet and dry climates 280 00:15:10,577 --> 00:15:12,911 that produce this 20,000-year cycle 281 00:15:12,913 --> 00:15:16,948 is what we see in the sahara, 282 00:15:16,950 --> 00:15:19,117 where at times of strong monsoon, 283 00:15:19,119 --> 00:15:23,421 the sahara is wetter, a green sahara. 284 00:15:23,423 --> 00:15:25,156 Narrator: 10,000 years ago, 285 00:15:25,158 --> 00:15:27,592 as the earth wobbled around the sun, 286 00:15:27,594 --> 00:15:32,697 monsoons were unleashed, turning the desert green. 287 00:15:32,699 --> 00:15:35,767 Humans migrated to the newly lush sahara 288 00:15:35,769 --> 00:15:38,803 and created the cave paintings we see today. 289 00:15:38,805 --> 00:15:40,939 ♪ 290 00:15:40,941 --> 00:15:45,376 but this wasn't the first time humans crossed a green sahara. 291 00:15:45,378 --> 00:15:48,212 ♪ 292 00:15:48,214 --> 00:15:51,049 dartnell: A dry sahara would have presented 293 00:15:51,051 --> 00:15:53,451 an insurmountable barrier 294 00:15:53,453 --> 00:15:57,155 to our ancestors for migrating out of africa, 295 00:15:57,157 --> 00:16:02,260 but during one of these cycles when the sahara was green, 296 00:16:02,262 --> 00:16:04,028 it would have been a corridor 297 00:16:04,030 --> 00:16:06,130 that we could have migrated and dispersed on. 298 00:16:06,132 --> 00:16:08,232 ♪ 299 00:16:08,234 --> 00:16:10,234 narrator: As the earth traveled the cosmos, 300 00:16:10,236 --> 00:16:13,304 our planet's precession changed the sahara 301 00:16:13,306 --> 00:16:18,543 and the fate of humankind, but there are more cosmic forces 302 00:16:18,545 --> 00:16:22,313 affecting our journey through the universe. 303 00:16:22,315 --> 00:16:24,382 The earth's orbit around the sun is another thing 304 00:16:24,384 --> 00:16:26,017 that seems very, very solid. 305 00:16:26,019 --> 00:16:29,120 We understand how it works, but everything in the universe 306 00:16:29,122 --> 00:16:31,723 is a delicately tuned dance of gravity, 307 00:16:31,725 --> 00:16:36,861 and things can change even from tiny little influences. 308 00:16:36,863 --> 00:16:39,364 Narrator: As our planet hurtles through space, 309 00:16:39,366 --> 00:16:43,534 other worlds influence our path. 310 00:16:43,536 --> 00:16:48,339 Could a planetary bully push earth's climate to the extreme? 311 00:16:48,341 --> 00:16:51,843 [ ice cracking ] 312 00:16:54,314 --> 00:17:00,985 ♪ 313 00:17:00,987 --> 00:17:04,856 narrator: Earth carries us on a wild journey through the cosmos. 314 00:17:04,858 --> 00:17:07,592 ♪ 315 00:17:07,594 --> 00:17:09,894 and clues to the effects of this trip 316 00:17:09,896 --> 00:17:12,030 are hiding in our own backyard. 317 00:17:12,032 --> 00:17:17,168 ♪ 318 00:17:17,170 --> 00:17:20,171 [ car horns honking ] 319 00:17:20,173 --> 00:17:22,206 ♪ 320 00:17:22,208 --> 00:17:27,245 in new york city, amongst the buildings and traffic, 321 00:17:27,247 --> 00:17:30,281 we find moraines, 322 00:17:30,283 --> 00:17:33,751 rocks left behind by retreating glaciers. 323 00:17:33,753 --> 00:17:38,389 ♪ 324 00:17:38,391 --> 00:17:39,957 18,000 years ago, 325 00:17:39,959 --> 00:17:46,097 a sheet of ice taller than any skyscraper covered manhattan. 326 00:17:46,099 --> 00:17:50,001 Ice ages have struck regularly throughout earth's history, 327 00:17:52,172 --> 00:17:55,039 putting our planet in a deep freeze. 328 00:17:55,041 --> 00:17:58,076 [ ice cracking ] 329 00:17:58,078 --> 00:17:59,710 durda: There was a period in earth's history 330 00:17:59,712 --> 00:18:01,746 several hundred million years ago, 331 00:18:01,748 --> 00:18:02,980 the snowball earth period, 332 00:18:02,982 --> 00:18:06,017 when we went through a very extreme glaciation, 333 00:18:06,019 --> 00:18:07,418 if you will, a very extreme ice age 334 00:18:07,420 --> 00:18:09,687 where we think perhaps the entire earth 335 00:18:09,689 --> 00:18:11,289 was covered in an ice sheet. 336 00:18:13,259 --> 00:18:15,993 Narrator: The trigger? 337 00:18:15,995 --> 00:18:18,963 Earth's orbital dance around the sun. 338 00:18:18,965 --> 00:18:21,999 ♪ 339 00:18:22,001 --> 00:18:23,201 we tend to think of ourselves 340 00:18:23,203 --> 00:18:24,902 sitting relatively stationary on the earth. 341 00:18:24,904 --> 00:18:26,637 It's pretty comforting, actually, 342 00:18:26,639 --> 00:18:32,176 but we're orbiting the sun at about 66,000 miles per hour. 343 00:18:32,178 --> 00:18:36,147 Narrator: Every day, earth travels over 1.6 million miles 344 00:18:36,149 --> 00:18:40,017 on its journey around the sun. 345 00:18:40,019 --> 00:18:43,121 This orbit isn't always completely round. 346 00:18:43,123 --> 00:18:47,091 ♪ 347 00:18:47,093 --> 00:18:48,826 earth is generally going around the sun 348 00:18:48,828 --> 00:18:51,529 in more or less a circular orbit, 349 00:18:51,531 --> 00:18:56,200 but over time, the massaging of this orbit from the sun, 350 00:18:56,202 --> 00:18:58,536 from the moon on the earth's orbit 351 00:18:58,538 --> 00:19:02,006 causes the orbit of the earth to change 352 00:19:02,008 --> 00:19:03,674 so that sometimes it's an ellipse. 353 00:19:03,676 --> 00:19:05,476 Sometimes it's more of a circle. 354 00:19:05,478 --> 00:19:08,146 ♪ 355 00:19:08,148 --> 00:19:09,580 right now on the earth, 356 00:19:09,582 --> 00:19:12,150 we're in kind of the most circular time in the orbit, 357 00:19:12,152 --> 00:19:14,819 so that means the summers are relatively mild, 358 00:19:14,821 --> 00:19:16,821 and the winters are relatively mild, 359 00:19:16,823 --> 00:19:19,190 but imagine not that long ago in the past, 360 00:19:19,192 --> 00:19:22,593 it could have been really dramatically different. 361 00:19:22,595 --> 00:19:26,164 When the earth is a little bit closer to the sun, 362 00:19:26,166 --> 00:19:28,466 maybe you have a really severe summer, 363 00:19:28,468 --> 00:19:29,901 and then on the other side of the orbit, 364 00:19:29,903 --> 00:19:31,602 you're a little farther away from the sun than normal, 365 00:19:31,604 --> 00:19:33,671 so you have a really severe winter. 366 00:19:33,673 --> 00:19:37,108 ♪ 367 00:19:37,110 --> 00:19:40,878 our environment is very, very sensitive to these things, 368 00:19:40,880 --> 00:19:42,914 and when the earth's orbit is stretched out, 369 00:19:42,916 --> 00:19:45,349 that can actually trigger an ice age. 370 00:19:45,351 --> 00:19:48,986 ♪ 371 00:19:48,988 --> 00:19:51,789 narrator: Our planet's 100,000-year orbital cycle 372 00:19:51,791 --> 00:19:54,592 caused the ice age that buried new york. 373 00:19:58,798 --> 00:20:04,635 And ice ages have had a big effect on human history. 374 00:20:04,637 --> 00:20:06,437 15,000 years ago, 375 00:20:06,439 --> 00:20:08,739 plunging temperatures locked water away 376 00:20:08,741 --> 00:20:11,542 in glaciers and ice caps. 377 00:20:11,544 --> 00:20:17,415 Sea levels dropped, creating land bridges between continents. 378 00:20:17,417 --> 00:20:22,420 Humans migrated from asia to america by foot, 379 00:20:22,422 --> 00:20:26,157 and for the first time, america was inhabited. 380 00:20:26,159 --> 00:20:29,527 ♪ 381 00:20:29,529 --> 00:20:34,498 may 2018 -- scientists revealed a whole new dynamic 382 00:20:34,500 --> 00:20:36,100 to earth's journey. 383 00:20:36,102 --> 00:20:38,269 ♪ 384 00:20:38,271 --> 00:20:41,072 every 405,000 years, 385 00:20:41,074 --> 00:20:45,243 our planet's orbital voyage stretches to the extreme, 386 00:20:45,245 --> 00:20:50,414 and earth's planetary neighbors are to blame. 387 00:20:50,416 --> 00:20:52,850 Because jupiter is the most massive planet 388 00:20:52,852 --> 00:20:54,218 in our solar system, 389 00:20:54,220 --> 00:20:57,221 it is in many ways the bully on the playground, right? 390 00:20:57,223 --> 00:21:00,725 Its dynamics, its gravity sculpts a lot of the dynamics 391 00:21:00,727 --> 00:21:02,326 of the solar system. 392 00:21:02,328 --> 00:21:04,562 ♪ 393 00:21:04,564 --> 00:21:06,797 durda: It actually tugs and pulls on the orbit 394 00:21:06,799 --> 00:21:08,299 of the earth itself. 395 00:21:08,301 --> 00:21:10,501 It's responsible for some of the very changes 396 00:21:10,503 --> 00:21:13,170 that drive our climatic cycle here on our planet. 397 00:21:13,172 --> 00:21:16,307 ♪ 398 00:21:16,309 --> 00:21:19,010 narrator: Jupiter isn't the only bully in the playground. 399 00:21:19,012 --> 00:21:20,878 ♪ 400 00:21:20,880 --> 00:21:22,580 thaller: Venus is a fairly big planet 401 00:21:22,582 --> 00:21:24,282 about the size of the earth 402 00:21:24,284 --> 00:21:26,684 and also comes closest to us in its orbit, 403 00:21:26,686 --> 00:21:30,254 so these two planets put just a little tiny elongation 404 00:21:30,256 --> 00:21:31,789 onto our earth's orbit, 405 00:21:31,791 --> 00:21:34,458 and as the cycle continues, the more extreme it gets, 406 00:21:34,460 --> 00:21:36,594 we can actually notice a temperature difference 407 00:21:36,596 --> 00:21:40,230 that happens about once every 405,000 years. 408 00:21:40,232 --> 00:21:43,501 ♪ 409 00:21:43,503 --> 00:21:47,038 narrator: Jupiter and venus gang up on earth gravitationally, 410 00:21:47,040 --> 00:21:52,243 pulling earth's orbit into an even greater ellipse. 411 00:21:52,245 --> 00:21:54,845 Our planet's hot weather becomes hotter, 412 00:21:54,847 --> 00:21:58,082 and its cold weather gets much colder. 413 00:21:58,084 --> 00:22:02,887 ♪ 414 00:22:02,889 --> 00:22:05,756 today, we're in a moderate part of the cycle, 415 00:22:05,758 --> 00:22:08,659 but in just 60,000 years time, 416 00:22:08,661 --> 00:22:14,031 we could plunge into another deep freeze. 417 00:22:14,033 --> 00:22:16,067 It's a little bit like a cosmic butterfly effect. 418 00:22:16,069 --> 00:22:18,235 I mean, even the smallest effects 419 00:22:18,237 --> 00:22:21,539 can have, you know, a big influence over time. 420 00:22:21,541 --> 00:22:24,542 ♪ 421 00:22:24,544 --> 00:22:26,110 narrator: Earth's orbit around the sun 422 00:22:26,112 --> 00:22:29,680 is just part of our far larger cosmic journey. 423 00:22:29,682 --> 00:22:32,249 ♪ 424 00:22:32,251 --> 00:22:35,753 the entire solar system is hurtling around the milky way, 425 00:22:35,755 --> 00:22:38,856 ♪ 426 00:22:38,858 --> 00:22:43,227 taking us places we don't want to be. 427 00:22:43,229 --> 00:22:45,796 Sometimes our planet might wander 428 00:22:45,798 --> 00:22:48,466 into what's essentially a bad neighborhood. 429 00:22:48,468 --> 00:22:50,267 Narrator: What dangers await us? 430 00:22:50,269 --> 00:22:53,671 And could these neighborhoods spell disaster 431 00:22:53,673 --> 00:22:55,272 for life on earth? 432 00:22:56,809 --> 00:23:03,414 ♪ 433 00:23:03,416 --> 00:23:09,954 ♪ 434 00:23:09,956 --> 00:23:14,291 narrator: Over the last 3.7 billion years, 435 00:23:14,293 --> 00:23:16,961 a series of extinction events wiped out 436 00:23:16,963 --> 00:23:20,898 almost 95 percent of all species on earth. 437 00:23:22,568 --> 00:23:24,769 [ explosion ] 438 00:23:24,771 --> 00:23:28,038 ♪ 439 00:23:28,040 --> 00:23:30,908 now research suggests our planet's orbit 440 00:23:30,910 --> 00:23:33,277 could be partly to blame, 441 00:23:33,279 --> 00:23:36,714 but not the earth's orbit around the sun, 442 00:23:36,716 --> 00:23:42,253 our planet's larger and longer journey around the milky way. 443 00:23:42,255 --> 00:23:45,456 Our solar system and our sun is shooting through the galaxy 444 00:23:45,458 --> 00:23:51,395 at about 530,000 miles per hour around the center of our galaxy. 445 00:23:51,397 --> 00:23:54,665 And that center of the galaxy is about 26,000 light-years away, 446 00:23:54,667 --> 00:23:57,735 so it should take the sun about 230 million years 447 00:23:57,737 --> 00:24:01,038 to trace out one full orbit around the center of the galaxy. 448 00:24:01,040 --> 00:24:03,574 ♪ 449 00:24:03,576 --> 00:24:05,609 narrator: Despite racing around the milky way 450 00:24:05,611 --> 00:24:08,913 at 1/2 million miles an hour, 451 00:24:08,915 --> 00:24:12,716 earth has completed less than 20 laps of the galaxy 452 00:24:12,718 --> 00:24:16,520 in our planet's entire history, 453 00:24:16,522 --> 00:24:19,990 and it turns out this galactic ride 454 00:24:19,992 --> 00:24:22,860 is more complicated than it seems. 455 00:24:22,862 --> 00:24:24,995 Now, if you look at the earth going around the sun, 456 00:24:24,997 --> 00:24:26,430 it defines an ellipse, 457 00:24:26,432 --> 00:24:28,933 but that's a flat figure, and you'd think, 458 00:24:28,935 --> 00:24:32,336 "well, the sun probably goes around in a plane, as well," 459 00:24:32,338 --> 00:24:34,805 and it turns out not that simple. 460 00:24:34,807 --> 00:24:37,641 ♪ 461 00:24:37,643 --> 00:24:39,777 narrator: Most of the mass of the solar system 462 00:24:39,779 --> 00:24:42,079 is concentrated in the sun, 463 00:24:42,081 --> 00:24:46,784 so earth and the other planets smoothly orbit our star. 464 00:24:46,786 --> 00:24:50,187 ♪ 465 00:24:50,189 --> 00:24:55,359 but the mass of the milky way is spread out unevenly. 466 00:24:55,361 --> 00:24:57,862 That changes the gravity of the galaxy, 467 00:24:57,864 --> 00:25:00,831 and so it changes how things move in it, and in fact, 468 00:25:00,833 --> 00:25:03,934 if you give something a little bit of an up or down motion, 469 00:25:03,936 --> 00:25:07,371 it'll bob up and down as it goes around. 470 00:25:07,373 --> 00:25:10,574 Oluseyi: Riding the earth is almost like riding a carousel. 471 00:25:10,576 --> 00:25:13,477 As the sun and the earth go around the galaxy, 472 00:25:13,479 --> 00:25:15,246 the sun also goes up and down 473 00:25:15,248 --> 00:25:17,381 like you're on one of those horses with the pole, 474 00:25:17,383 --> 00:25:19,049 and so what this can do 475 00:25:19,051 --> 00:25:22,820 is take us into different galactic environments. 476 00:25:22,822 --> 00:25:26,156 ♪ 477 00:25:26,158 --> 00:25:29,426 narrator: This bobbing motion takes earth and the solar system 478 00:25:29,428 --> 00:25:31,662 on a 60,000-year journey 479 00:25:31,664 --> 00:25:35,432 up and down through the milky way's galactic plane. 480 00:25:35,434 --> 00:25:37,868 ♪ 481 00:25:37,870 --> 00:25:39,370 our orbit also takes us 482 00:25:39,372 --> 00:25:41,872 through different galactic neighborhoods. 483 00:25:41,874 --> 00:25:45,376 ♪ 484 00:25:45,378 --> 00:25:50,948 today, we're traveling through a calm suburb of the galaxy. 485 00:25:50,950 --> 00:25:55,352 But sometimes things get a little bumpy. 486 00:25:55,354 --> 00:25:59,089 Sometimes our sun and our planet might wander 487 00:25:59,091 --> 00:26:01,659 into what's essentially a bad neighborhood. 488 00:26:01,661 --> 00:26:02,993 You know, maybe it's an area 489 00:26:02,995 --> 00:26:04,962 where there's a lot of star formation going on, 490 00:26:04,964 --> 00:26:07,898 where there's a lot of young stars that are very active, 491 00:26:07,900 --> 00:26:11,101 or maybe it's a location where there are dying stars, 492 00:26:11,103 --> 00:26:14,104 and things are about to get really hot. 493 00:26:14,106 --> 00:26:16,774 Narrator: The baddest neighborhoods in the galaxy 494 00:26:16,776 --> 00:26:19,310 may be the spiral arms. 495 00:26:19,312 --> 00:26:21,845 ♪ 496 00:26:21,847 --> 00:26:25,282 these gas-filled regions orbit the galactic center 497 00:26:25,284 --> 00:26:28,819 more slowly than the earth, 498 00:26:28,821 --> 00:26:31,989 so our planet passes through an arm 499 00:26:31,991 --> 00:26:35,559 roughly every 150 million years. 500 00:26:35,561 --> 00:26:39,296 Plait: These arms are where gas clouds tend to hang out, 501 00:26:39,298 --> 00:26:43,834 and if they get compressed, they form a lot of stars. 502 00:26:43,836 --> 00:26:48,205 When they form a lot of stars, they make bright, blue stars. 503 00:26:48,207 --> 00:26:51,642 And they don't last long, and they blow up as supernovae. 504 00:26:51,644 --> 00:26:56,680 ♪ 505 00:26:56,682 --> 00:27:00,351 [ explosion ] 506 00:27:00,353 --> 00:27:03,887 so it's possible that as we're passing through these regions, 507 00:27:03,889 --> 00:27:06,824 these are places you might not want to be in, 508 00:27:06,826 --> 00:27:08,225 so in the distant past, 509 00:27:08,227 --> 00:27:10,127 this may have affected the earth. 510 00:27:10,129 --> 00:27:15,432 ♪ 511 00:27:15,434 --> 00:27:17,501 narrator: When giant stars go supernova, 512 00:27:17,503 --> 00:27:20,237 the stars' outer layers blast into space 513 00:27:20,239 --> 00:27:23,907 ♪ 514 00:27:23,909 --> 00:27:25,409 along with a shock wave 515 00:27:25,411 --> 00:27:28,212 traveling at 20,000 miles a second. 516 00:27:28,214 --> 00:27:31,615 ♪ 517 00:27:31,617 --> 00:27:37,154 supernovas also release cosmic rays -- 518 00:27:37,156 --> 00:27:39,890 space bullets that shoot across the galaxy 519 00:27:39,892 --> 00:27:41,792 at close to the speed of light. 520 00:27:41,794 --> 00:27:44,461 ♪ 521 00:27:44,463 --> 00:27:46,630 plait: And you don't want to be exposed to too many of them, 522 00:27:46,632 --> 00:27:47,998 but in high enough doses, 523 00:27:48,000 --> 00:27:50,634 these things penetrate our cells and damage our dna 524 00:27:50,636 --> 00:27:54,538 and over the long-term can cause really bad damage 525 00:27:54,540 --> 00:27:57,074 to human bodies. 526 00:27:57,076 --> 00:27:58,676 Narrator: As we ride through space, 527 00:27:58,678 --> 00:28:04,782 earth's magnetic field protects us from most cosmic rays. 528 00:28:04,784 --> 00:28:08,719 But in 2018, we discovered evidence 529 00:28:08,721 --> 00:28:10,688 that a hail of space bullets 530 00:28:10,690 --> 00:28:15,559 overwhelmed our planet's magnetic field in the past. 531 00:28:15,561 --> 00:28:17,561 In many ways, we really take for granted 532 00:28:17,563 --> 00:28:20,631 how the earth protects us from space, 533 00:28:20,633 --> 00:28:22,199 but there are records that we've actually bounced 534 00:28:22,201 --> 00:28:25,869 a little too close to exploding stars. 535 00:28:25,871 --> 00:28:28,005 Plait: Sediments in the ocean show that 536 00:28:28,007 --> 00:28:30,107 about 2 million years ago, 537 00:28:30,109 --> 00:28:33,310 iron-60 was deposited in our oceans. 538 00:28:33,312 --> 00:28:36,046 Iron-60 is a radioactive isotope of iron, 539 00:28:36,048 --> 00:28:38,749 and there's only way we know of it being made in the universe, 540 00:28:38,751 --> 00:28:41,351 and that is exploding stars. 541 00:28:41,353 --> 00:28:45,689 ♪ 542 00:28:45,691 --> 00:28:47,725 narrator: Around 2.8 million years ago, 543 00:28:47,727 --> 00:28:52,162 a supernova exploded just 150 light-years from earth. 544 00:28:54,567 --> 00:28:56,200 A few hundred years later, 545 00:28:56,202 --> 00:29:00,104 a blizzard of cosmic rays slammed into the earth, 546 00:29:00,106 --> 00:29:02,406 tearing through our magnetic field. 547 00:29:02,408 --> 00:29:06,443 ♪ 548 00:29:06,445 --> 00:29:10,481 these space bullets are prime suspect in the extinction 549 00:29:10,483 --> 00:29:13,450 of over 1/3 of all coastal marine species. 550 00:29:13,452 --> 00:29:16,120 ♪ 551 00:29:16,122 --> 00:29:18,422 plait: Now, this is not necessarily tied to the earth 552 00:29:18,424 --> 00:29:21,125 passing through one of these spiral arms, 553 00:29:21,127 --> 00:29:23,861 but it shows you that being close to a supernova 554 00:29:23,863 --> 00:29:28,098 is not necessarily a thing you want to do. 555 00:29:28,100 --> 00:29:30,067 Narrator: Millions of years in the future, 556 00:29:30,069 --> 00:29:33,637 earth will pass through another spiral arm 557 00:29:33,639 --> 00:29:39,409 as our planet continues its journey through the milky way. 558 00:29:39,411 --> 00:29:43,781 And we will wander into harm's way once again. 559 00:29:46,619 --> 00:29:49,019 But there's another part of our journey through space 560 00:29:49,021 --> 00:29:51,889 that remains a mystery. 561 00:29:51,891 --> 00:29:54,825 The earth is spinning like a top on its axis. 562 00:29:54,827 --> 00:29:56,260 It's orbiting around the sun. 563 00:29:56,262 --> 00:29:58,662 The sun itself is orbiting around the center 564 00:29:58,664 --> 00:30:03,500 of the milky way, but that's far from it. 565 00:30:03,502 --> 00:30:06,170 Narrator: The milky way is speeding through the universe, 566 00:30:06,172 --> 00:30:11,375 and we are being dragged along for the ride. 567 00:30:11,377 --> 00:30:14,912 The problem is we can't see where we're going. 568 00:30:14,914 --> 00:30:18,582 Could earth be headed for a galactic crash? 569 00:30:18,584 --> 00:30:20,851 ♪ 570 00:30:22,388 --> 00:30:27,658 ♪ 571 00:30:27,660 --> 00:30:30,627 [ screaming ] 572 00:30:30,629 --> 00:30:32,763 ♪ 573 00:30:32,765 --> 00:30:35,399 narrator: Like the craziest of theme park rides, 574 00:30:35,401 --> 00:30:39,703 we are riding the earth on a wild journey through the cosmos. 575 00:30:39,705 --> 00:30:46,443 ♪ 576 00:30:46,445 --> 00:30:50,981 our planet spins, tilts, and wobbles around the solar system 577 00:30:50,983 --> 00:30:53,116 ♪ 578 00:30:53,118 --> 00:30:56,720 while bobbing like a carousel through the milky way. 579 00:30:56,722 --> 00:30:59,223 ♪ 580 00:30:59,225 --> 00:31:03,026 the dynamics of the earth moving in the cosmic void is, 581 00:31:03,028 --> 00:31:06,697 like, the most unbelievable journey you could ever imagine, 582 00:31:06,699 --> 00:31:08,699 and as you get to larger scales, 583 00:31:08,701 --> 00:31:12,169 the motions only become grander and larger and more dynamic. 584 00:31:12,171 --> 00:31:16,039 ♪ 585 00:31:16,041 --> 00:31:19,176 narrator: In 1977, we tried to work out 586 00:31:19,178 --> 00:31:21,078 the largest motion of all -- 587 00:31:21,080 --> 00:31:23,647 ♪ 588 00:31:23,649 --> 00:31:27,851 the movement of our galaxy through the universe. 589 00:31:27,853 --> 00:31:31,154 Clues hide in the cosmic microwave background, 590 00:31:31,156 --> 00:31:34,524 a remnant from the birth of the universe. 591 00:31:34,526 --> 00:31:37,094 Bullock: The cosmic microwave background is the radiation 592 00:31:37,096 --> 00:31:40,397 that's left over from the hot big bang. 593 00:31:40,399 --> 00:31:43,166 The cosmic microwave background is shining in all directions 594 00:31:43,168 --> 00:31:44,902 as sort of this fixed thing, 595 00:31:44,904 --> 00:31:47,337 and if we're moving through it with some speed, 596 00:31:47,339 --> 00:31:49,373 we will see that in the light itself. 597 00:31:49,375 --> 00:31:51,275 You can measure that, and by measuring that, 598 00:31:51,277 --> 00:31:55,946 you can get a sense of how fast we're moving through that space. 599 00:31:55,948 --> 00:31:58,115 Narrator: By tracking our movement through the universe 600 00:31:58,117 --> 00:31:59,716 against a fixed point, 601 00:31:59,718 --> 00:32:03,553 we can work out the milky way's speed and direction. 602 00:32:03,555 --> 00:32:06,390 ♪ 603 00:32:06,392 --> 00:32:13,030 but in 1977, telescopes weren't the best tool for the job. 604 00:32:13,032 --> 00:32:15,565 Tremblay: During the cold war, 1977, 605 00:32:15,567 --> 00:32:18,201 you have the newly declassified u-2 spy plane, 606 00:32:18,203 --> 00:32:21,238 this very high-altitude reconnaissance aircraft. 607 00:32:21,240 --> 00:32:24,775 Nasa retrofitted one of them with an upward-facing window, 608 00:32:24,777 --> 00:32:26,710 and with very sensitive receivers, 609 00:32:26,712 --> 00:32:29,379 this spy plane became the first experiment 610 00:32:29,381 --> 00:32:32,849 to for the first time definitively measure the motion 611 00:32:32,851 --> 00:32:35,018 of the galaxy through the universe. 612 00:32:35,020 --> 00:32:38,121 Narrator: As the u-2 spy plane soared above the earth, 613 00:32:38,123 --> 00:32:41,024 it measured the cosmic microwave background 614 00:32:41,026 --> 00:32:42,893 in unprecedented detail. 615 00:32:42,895 --> 00:32:46,096 ♪ 616 00:32:46,098 --> 00:32:49,366 the data revealed that our galaxy races 617 00:32:49,368 --> 00:32:53,537 through the universe at 370 miles a second. 618 00:32:53,539 --> 00:32:57,374 ♪ 619 00:32:57,376 --> 00:32:59,476 that's over 1 million miles an hour. 620 00:32:59,478 --> 00:33:03,347 ♪ 621 00:33:03,349 --> 00:33:05,949 sutter: Think of how big a galaxy is. 622 00:33:05,951 --> 00:33:08,819 Hundreds of millions of stars, 623 00:33:08,821 --> 00:33:12,622 and we're moving at hundreds of miles per second. 624 00:33:12,624 --> 00:33:14,725 That's just a tiny bit mind-blowing. 625 00:33:14,727 --> 00:33:16,860 ♪ 626 00:33:16,862 --> 00:33:20,130 narrator: The milky way's speed isn't the most alarming part 627 00:33:20,132 --> 00:33:22,766 of our galactic journey. 628 00:33:22,768 --> 00:33:26,703 From earth, we can't even see in the direction our galaxy 629 00:33:26,705 --> 00:33:28,071 is taking us. 630 00:33:28,073 --> 00:33:29,639 We're flying blind. 631 00:33:29,641 --> 00:33:33,110 Our view is blocked by the milky way itself. 632 00:33:33,112 --> 00:33:36,079 ♪ 633 00:33:36,081 --> 00:33:38,682 so if you're actually looking through the plane of the galaxy, 634 00:33:38,684 --> 00:33:40,584 through the plane of the pancake, 635 00:33:40,586 --> 00:33:43,220 your view of the galaxy is obscured 636 00:33:43,222 --> 00:33:47,924 by curtains of dust and gas that envelop our solar system. 637 00:33:47,926 --> 00:33:49,726 Bullock: It's very bright. There's a lot of stars. 638 00:33:49,728 --> 00:33:53,130 And our view is blocked by the galaxy itself, 639 00:33:53,132 --> 00:33:56,166 so there's a zone directly behind the galaxy 640 00:33:56,168 --> 00:33:58,402 as we look towards the galactic center 641 00:33:58,404 --> 00:34:00,270 that's really an unknown area. 642 00:34:00,272 --> 00:34:02,305 It's a zone we call the zone of avoidance, 643 00:34:02,307 --> 00:34:05,075 and it's an area of really cosmic mystery. 644 00:34:05,077 --> 00:34:07,310 ♪ 645 00:34:07,312 --> 00:34:11,081 narrator: Thanks to this mysterious zone, 646 00:34:11,083 --> 00:34:14,851 we thought we could be headed for a galactic car crash. 647 00:34:14,853 --> 00:34:20,323 ♪ 648 00:34:20,325 --> 00:34:22,459 then we had a breakthrough. 649 00:34:22,461 --> 00:34:28,665 ♪ 650 00:34:28,667 --> 00:34:31,268 we used powerful radio telescopes 651 00:34:31,270 --> 00:34:33,570 to look through the zone of avoidance 652 00:34:33,572 --> 00:34:35,072 for the first time. 653 00:34:35,074 --> 00:34:41,678 ♪ 654 00:34:41,680 --> 00:34:44,247 bullock: One of the nice things about using light that's 655 00:34:44,249 --> 00:34:47,784 in the radio is that this kind of light actually can go through 656 00:34:47,786 --> 00:34:50,353 pretty dense kinds of gas and stars 657 00:34:50,355 --> 00:34:53,757 and allows us to sort of look through things. 658 00:34:53,759 --> 00:34:55,926 Using these radio telescopes has given us a glimpse 659 00:34:55,928 --> 00:35:00,530 into what lies beyond the zone of avoidance. 660 00:35:00,532 --> 00:35:03,366 Narrator: Peering through the zone of avoidance, 661 00:35:03,368 --> 00:35:07,070 we found that the milky way's path is clear, 662 00:35:07,072 --> 00:35:08,872 but that's not all. 663 00:35:08,874 --> 00:35:12,442 We also discovered we are just one tiny part 664 00:35:12,444 --> 00:35:14,978 of a vast cluster of galaxies 665 00:35:14,980 --> 00:35:18,081 sailing through the cosmos together. 666 00:35:18,083 --> 00:35:20,383 We think that our galaxy, the milky way, 667 00:35:20,385 --> 00:35:24,354 is part of a much grander cosmic flow of galaxies, 668 00:35:24,356 --> 00:35:26,056 and it is part of what might be 669 00:35:26,058 --> 00:35:28,391 the laniakea supercluster of galaxies, 670 00:35:28,393 --> 00:35:30,861 this giant, giant cosmic structure 671 00:35:30,863 --> 00:35:33,463 filled with potentially thousands of galaxies 672 00:35:33,465 --> 00:35:35,565 that is moving together in this beautiful, 673 00:35:35,567 --> 00:35:37,400 like, slow-moving river 674 00:35:37,402 --> 00:35:40,437 that is sculpted and dictated by gravity itself. 675 00:35:40,439 --> 00:35:43,206 ♪ 676 00:35:43,208 --> 00:35:47,043 narrator: Earth voyages through space along gravitational rivers 677 00:35:47,045 --> 00:35:50,680 hundreds of millions of light-years long 678 00:35:50,682 --> 00:35:54,618 along with a fleet of 100,000 other galaxies, 679 00:35:54,620 --> 00:35:58,622 all moving toward a single point in space, 680 00:35:58,624 --> 00:36:04,728 a gravitational drain known as the great attractor. 681 00:36:04,730 --> 00:36:10,500 Sutter: The great attractor is the local region of gravity, 682 00:36:10,502 --> 00:36:13,670 of strong gravity in this patch of the universe. 683 00:36:13,672 --> 00:36:16,973 It's where all the galaxies in this chunk of the universe 684 00:36:16,975 --> 00:36:20,043 are flowing towards. 685 00:36:20,045 --> 00:36:22,812 At the location of the great attractor 686 00:36:22,814 --> 00:36:23,980 is a bunch of material -- 687 00:36:23,982 --> 00:36:25,882 a bunch of gas, a bunch of galaxies, 688 00:36:25,884 --> 00:36:29,085 an extremely massive cluster, 689 00:36:29,087 --> 00:36:33,290 and over time, more and more galaxies 690 00:36:33,292 --> 00:36:35,659 add themselves to this cluster 691 00:36:35,661 --> 00:36:40,230 as they continue to join the great attractor. 692 00:36:40,232 --> 00:36:42,933 Narrator: It's unlikely earth will ever reach 693 00:36:42,935 --> 00:36:45,669 the great attractor. 694 00:36:45,671 --> 00:36:52,442 It seems the milky way is headed for a collision after all. 695 00:36:52,444 --> 00:36:55,579 Is this how our cosmic journey ends? 696 00:36:55,581 --> 00:36:57,280 ♪ 697 00:36:58,650 --> 00:37:06,890 ♪ 698 00:37:06,892 --> 00:37:08,959 narrator: Earth's voyage across the cosmos 699 00:37:08,961 --> 00:37:12,762 has lasted for 4.5 billion years. 700 00:37:12,764 --> 00:37:17,634 ♪ 701 00:37:17,636 --> 00:37:21,938 the big question -- how will our journey finally end? 702 00:37:21,940 --> 00:37:25,008 ♪ 703 00:37:25,010 --> 00:37:27,043 a clue comes from the milky way's 704 00:37:27,045 --> 00:37:31,114 traveling companion -- another galaxy, andromeda, 705 00:37:31,116 --> 00:37:34,584 ♪ 706 00:37:34,586 --> 00:37:37,320 filled with up to a trillion stars 707 00:37:37,322 --> 00:37:40,090 that's charting a similar path to us. 708 00:37:40,092 --> 00:37:44,995 ♪ 709 00:37:44,997 --> 00:37:47,897 the andromeda galaxy is another big spiral galaxy, 710 00:37:47,899 --> 00:37:49,532 a lot like our milky way, 711 00:37:49,534 --> 00:37:54,604 and it turns out the two of us are heading for each other. 712 00:37:54,606 --> 00:37:56,640 Narrator: Andromeda and the milky way 713 00:37:56,642 --> 00:38:00,677 are currently 2.5 million light-years apart, 714 00:38:00,679 --> 00:38:03,280 but they're hurtling towards each other 715 00:38:03,282 --> 00:38:06,016 at over 250,000 miles an hour. 716 00:38:06,018 --> 00:38:08,818 ♪ 717 00:38:08,820 --> 00:38:12,255 a collision is inevitable. 718 00:38:12,257 --> 00:38:13,923 Stricker: Galaxies colliding with each other 719 00:38:13,925 --> 00:38:15,759 sounds like science fiction, 720 00:38:15,761 --> 00:38:17,861 but the collision of the andromeda galaxy 721 00:38:17,863 --> 00:38:22,565 and the milky way galaxy will be a spectacular event. 722 00:38:22,567 --> 00:38:25,101 Oluseyi: When the andromeda and milky way galaxies collide, 723 00:38:25,103 --> 00:38:28,872 it's gonna be a ridiculous light show. 724 00:38:28,874 --> 00:38:32,876 The stars don't collide, but the giant clouds of gas do, 725 00:38:32,878 --> 00:38:35,111 and that's gonna trigger star formation, 726 00:38:35,113 --> 00:38:38,381 so we're gonna have what's known as a starburst galaxy. 727 00:38:38,383 --> 00:38:40,517 ♪ 728 00:38:40,519 --> 00:38:43,453 when andromeda finally merges with the milky way, 729 00:38:43,455 --> 00:38:45,488 all bets are off. 730 00:38:45,490 --> 00:38:48,525 All of a sudden, a system of hundreds of billions of stars 731 00:38:48,527 --> 00:38:52,362 will be added to our own, and there will be mass chaos, 732 00:38:52,364 --> 00:38:54,130 but one thing you can guarantee -- 733 00:38:54,132 --> 00:38:56,633 there is going to be celestial fireworks. 734 00:38:56,635 --> 00:38:59,869 ♪ 735 00:38:59,871 --> 00:39:02,939 narrator: This could be the biggest light show in history, 736 00:39:02,941 --> 00:39:07,911 resulting in the creation of a brand-new galaxy. 737 00:39:07,913 --> 00:39:11,214 We will have become one giant galaxy. 738 00:39:11,216 --> 00:39:13,483 Call it milkdromeda, if you will, 739 00:39:13,485 --> 00:39:15,251 so we will look very different. 740 00:39:15,253 --> 00:39:18,822 Our grand-design, spiral milky way galaxy 741 00:39:18,824 --> 00:39:21,891 will have probably transformed itself 742 00:39:21,893 --> 00:39:26,296 into an entirely different shape. 743 00:39:26,298 --> 00:39:28,531 Narrator: The merging galaxies could create 744 00:39:28,533 --> 00:39:31,668 a giant, elliptical-shaped galaxy, 745 00:39:31,670 --> 00:39:35,271 but earth might not be around to see it. 746 00:39:35,273 --> 00:39:38,742 Billions of stars are gonna come careening into our galaxy, 747 00:39:38,744 --> 00:39:43,012 very, very easily disrupting the orbit of the earth. 748 00:39:43,014 --> 00:39:46,049 The sun could be thrown out of the galaxy entirely. 749 00:39:46,051 --> 00:39:49,819 ♪ 750 00:39:49,821 --> 00:39:53,289 narrator: As stars, dust, and gas swirl around each other, 751 00:39:53,291 --> 00:39:55,959 ♪ 752 00:39:55,961 --> 00:40:00,096 gravitational interactions could slingshot our solar system 753 00:40:00,098 --> 00:40:02,799 out into intergalactic space. 754 00:40:02,801 --> 00:40:08,204 ♪ 755 00:40:08,206 --> 00:40:10,206 we'll still orbit the sun, and everything will be fine, 756 00:40:10,208 --> 00:40:11,841 kind of, but it just means 757 00:40:11,843 --> 00:40:14,110 we'll see something very different in our sky 758 00:40:14,112 --> 00:40:19,215 in 4.6 billion years than we do now. 759 00:40:19,217 --> 00:40:20,683 Narrator: Our planet could be sent 760 00:40:20,685 --> 00:40:23,686 on a whole new intergalactic ride, 761 00:40:23,688 --> 00:40:25,722 ♪ 762 00:40:25,724 --> 00:40:32,695 shot out into the cosmos, away from the new milkdromeda galaxy. 763 00:40:32,697 --> 00:40:35,098 There's no way of knowing exactly what's going to happen, 764 00:40:35,100 --> 00:40:38,101 and in that sense, journey's end... 765 00:40:38,103 --> 00:40:42,272 ♪ 766 00:40:42,274 --> 00:40:43,873 we'll just have to wait and see. 767 00:40:43,875 --> 00:40:51,414 ♪ 768 00:40:51,416 --> 00:40:53,850 narrator: We might not know the final destination 769 00:40:53,852 --> 00:40:57,887 for earth's cosmic journey, but we do know this -- 770 00:40:57,889 --> 00:41:02,425 so far, it has been an incredible ride. 771 00:41:02,427 --> 00:41:04,594 We've had a fantastic journey 772 00:41:04,596 --> 00:41:07,897 over the history of earth's existence. 773 00:41:07,899 --> 00:41:11,234 We may not be immediately aware of our motions 774 00:41:11,236 --> 00:41:14,437 through the universe, but that doesn't mean they're not there. 775 00:41:14,439 --> 00:41:16,806 ♪ 776 00:41:16,808 --> 00:41:18,508 many people think of the earth 777 00:41:18,510 --> 00:41:23,079 as this blue, calm marble in space. 778 00:41:23,081 --> 00:41:26,216 But in reality, it's violently ripping around the sun, 779 00:41:26,218 --> 00:41:28,952 and the sun is ripping about the galaxy. 780 00:41:28,954 --> 00:41:31,254 ♪ 781 00:41:31,256 --> 00:41:33,456 there's a lot of dynamics happening. 782 00:41:33,458 --> 00:41:35,525 ♪ 783 00:41:35,527 --> 00:41:37,293 it boggles the mind just to think 784 00:41:37,295 --> 00:41:41,664 of what the earth will have done. 785 00:41:41,666 --> 00:41:44,767 The earth will have actually orbited the sun 786 00:41:44,769 --> 00:41:46,202 10 billion times. 787 00:41:46,204 --> 00:41:49,606 It will have spun on its axis, like, a trillion times 788 00:41:49,608 --> 00:41:52,408 in a galaxy that's moving through space. 789 00:41:52,410 --> 00:41:55,545 [ exhales ] 790 00:41:55,547 --> 00:41:58,781 riding the earth is anything but a boring trip. 791 00:41:58,783 --> 00:42:03,520 ♪