1 00:00:02,202 --> 00:00:05,566 >> Earth, a 4.5-billion-year- 2 00:00:05,633 --> 00:00:09,963 old planet, still evolving. As 3 00:00:09,997 --> 00:00:12,361 continents shift and clash, 4 00:00:12,463 --> 00:00:15,093 volcanoes erupt, and glaciers 5 00:00:15,161 --> 00:00:18,258 grow and recede, the Earth's 6 00:00:18,359 --> 00:00:19,990 crust is carved in numerous 7 00:00:20,058 --> 00:00:22,622 and fascinating ways, leaving 8 00:00:22,690 --> 00:00:23,955 a trail of geological 9 00:00:23,989 --> 00:00:27,853 mysteries behind. In this 10 00:00:27,887 --> 00:00:31,317 episode, the Marianas Trench, 11 00:00:31,385 --> 00:00:33,216 the deepest point on Earth, is 12 00:00:33,317 --> 00:00:36,481 explored. Its sheer walls cut 13 00:00:36,582 --> 00:00:38,380 seven miles into the Pacific 14 00:00:38,414 --> 00:00:41,045 Ocean. The mystery of what 15 00:00:41,113 --> 00:00:43,044 created this deep, dark chasm 16 00:00:43,112 --> 00:00:44,810 takes science detectives on 17 00:00:44,844 --> 00:00:46,276 some of the most dangerous 18 00:00:46,310 --> 00:00:50,107 dives ever attempted, deep 19 00:00:50,175 --> 00:00:52,739 into the abyss. Scouring the 20 00:00:52,840 --> 00:00:54,471 ocean floor, scientists 21 00:00:54,539 --> 00:00:56,103 uncover a strange, 22 00:00:56,204 --> 00:00:57,903 undersea world of fiery 23 00:00:58,004 --> 00:01:00,700 mountains, bizarre mud 24 00:01:00,735 --> 00:01:04,232 volcanoes and the largest 25 00:01:04,267 --> 00:01:07,630 geological structure on Earth. 26 00:01:07,697 --> 00:01:09,263 Discoveries from this unique 27 00:01:09,330 --> 00:01:10,762 underwater world will 28 00:01:10,796 --> 00:01:11,861 revolutionize our 29 00:01:11,896 --> 00:01:13,527 understanding of the powerful 30 00:01:13,628 --> 00:01:15,259 forces that shape not just the 31 00:01:15,326 --> 00:01:17,725 trench, but the Earth itself. 32 00:01:17,735 --> 00:01:21,728 S01x02 The Deepest Place on Earth Original Air Date on February 17, 2009 33 00:01:25,754 --> 00:01:27,153 Hidden deep beneath the waves 34 00:01:27,220 --> 00:01:28,951 of the western Pacific lies 35 00:01:29,052 --> 00:01:33,115 the Marianas Trench, the 36 00:01:33,183 --> 00:01:34,848 deepest point of all the 37 00:01:34,916 --> 00:01:36,181 oceans. 38 00:01:38,946 --> 00:01:40,712 The first step on the journey 39 00:01:40,746 --> 00:01:41,844 of what created this 40 00:01:41,912 --> 00:01:43,576 mysterious scar in the Earth's 41 00:01:43,644 --> 00:01:45,842 crust, and how it continues to 42 00:01:45,909 --> 00:01:47,474 mold the planet, takes us 43 00:01:47,542 --> 00:01:50,539 back to 1872, when a British 44 00:01:50,607 --> 00:01:52,105 research vessel, HMS 45 00:01:52,173 --> 00:01:53,637 Challenger, set out on the 46 00:01:53,738 --> 00:01:55,636 first ever mission to map the 47 00:01:55,704 --> 00:01:57,169 ocean floor. 48 00:01:57,237 --> 00:01:58,335 >> Throughout most of recorded 49 00:01:58,369 --> 00:02:00,167 history, men had just assumed 50 00:02:00,268 --> 00:02:01,433 that, beyond a certain level, 51 00:02:01,534 --> 00:02:03,066 the sea was pretty flat, 52 00:02:03,133 --> 00:02:06,897 pretty dead, pretty lifeless. 53 00:02:06,964 --> 00:02:08,130 They weren't expecting to find 54 00:02:08,164 --> 00:02:12,227 anything very interesting. 55 00:02:12,328 --> 00:02:13,860 >> For four years, the 56 00:02:13,926 --> 00:02:15,126 Challenger crisscrossed the 57 00:02:15,193 --> 00:02:19,056 oceans, covering 70,000 miles, 58 00:02:19,124 --> 00:02:20,589 a third of the distance to the 59 00:02:20,690 --> 00:02:21,955 moon. 60 00:02:23,322 --> 00:02:25,019 The crew plumbed the depths 61 00:02:25,054 --> 00:02:27,752 every 140 miles, using a total 62 00:02:27,853 --> 00:02:30,716 of 249 miles of rope, and 63 00:02:30,751 --> 00:02:31,849 hundreds of pounds of 64 00:02:31,916 --> 00:02:35,481 lead weight. It was tedious, 65 00:02:35,548 --> 00:02:37,346 backbreaking work, but at the 66 00:02:37,381 --> 00:02:38,845 time, it was the only way to 67 00:02:38,912 --> 00:02:40,177 measure the depth of the ocean 68 00:02:40,245 --> 00:02:41,643 floor. 69 00:02:46,442 --> 00:02:47,507 When they got to the western 70 00:02:47,541 --> 00:02:49,373 Pacific, 200 miles off the 71 00:02:49,440 --> 00:02:51,238 island of Guam, the crew 72 00:02:51,272 --> 00:02:52,804 routinely lowered the rope for 73 00:02:52,904 --> 00:02:54,070 a measurement. 74 00:02:59,068 --> 00:03:00,599 But the weight kept on 75 00:03:00,700 --> 00:03:04,031 dropping and dropping. 76 00:03:04,065 --> 00:03:06,229 >> It's a big surprise! Nobody 77 00:03:06,330 --> 00:03:07,296 thought the ocean was this 78 00:03:07,330 --> 00:03:09,395 deep. So all of sudden we've 79 00:03:09,428 --> 00:03:11,593 got scientists saying, "Why 80 00:03:11,694 --> 00:03:14,025 is that?" 81 00:03:20,123 --> 00:03:21,488 >> Eventually, the weight 82 00:03:21,555 --> 00:03:24,586 struck the bottom at 4,475 83 00:03:24,654 --> 00:03:27,851 fathoms, nearly five miles 84 00:03:27,918 --> 00:03:31,282 beneath the ocean's surface. 85 00:03:31,383 --> 00:03:32,282 >> The scientists would be 86 00:03:32,382 --> 00:03:33,348 going, "Wow, we've found 87 00:03:33,382 --> 00:03:34,447 something and what does it 88 00:03:34,548 --> 00:03:37,079 mean? Is it a little hole? Is 89 00:03:37,180 --> 00:03:38,278 it a big hole? What kind of 90 00:03:38,346 --> 00:03:39,811 feature is it down there?" 91 00:03:39,878 --> 00:03:40,810 There--there's a whole lot 92 00:03:40,877 --> 00:03:41,975 of questions you get when you 93 00:03:42,077 --> 00:03:43,709 find this one spectacular 94 00:03:43,810 --> 00:03:44,908 reading. 95 00:03:47,140 --> 00:03:48,239 >> The Challenger expedition 96 00:03:48,340 --> 00:03:49,539 marked the birth of modern 97 00:03:49,605 --> 00:03:51,438 oceanography, and provided the 98 00:03:51,505 --> 00:03:53,236 first crude map of the ocean 99 00:03:53,338 --> 00:03:54,302 floor. 100 00:03:56,336 --> 00:03:58,067 It showed how the ocean floor 101 00:03:58,134 --> 00:03:59,666 gently slopes away from the 102 00:03:59,701 --> 00:04:01,398 land, and then plummets 103 00:04:01,499 --> 00:04:03,230 thousands of feet into vast 104 00:04:03,298 --> 00:04:05,496 flat plains. But the western 105 00:04:05,596 --> 00:04:07,494 Pacific is different. It drops 106 00:04:07,562 --> 00:04:10,226 off again, into the five mile 107 00:04:10,294 --> 00:04:12,825 deep hole, a hole that blew 108 00:04:12,859 --> 00:04:13,891 right out of t water the 109 00:04:13,958 --> 00:04:15,524 long-held belief that the sea 110 00:04:15,591 --> 00:04:16,890 floor was flat and 111 00:04:16,991 --> 00:04:18,954 featureless. 112 00:04:20,588 --> 00:04:23,786 And it spawned a mystery, 113 00:04:23,853 --> 00:04:24,785 because nobody could 114 00:04:24,886 --> 00:04:26,418 understand how this strange 115 00:04:26,519 --> 00:04:29,616 underwater feature came about. 116 00:04:29,684 --> 00:04:31,348 It would be 75 years before 117 00:04:31,416 --> 00:04:34,113 any answers emerged. It took a 118 00:04:34,148 --> 00:04:36,046 revolutionary new technology, 119 00:04:36,147 --> 00:04:37,577 sonar, to push the 120 00:04:37,679 --> 00:04:39,210 investigation forward to the 121 00:04:39,278 --> 00:04:42,108 next crucial stage. 122 00:04:48,206 --> 00:04:49,671 Sonar was first developed in 123 00:04:49,738 --> 00:04:51,370 the early 1900s and then 124 00:04:51,438 --> 00:04:53,635 perfected during the 1940s to 125 00:04:53,670 --> 00:04:55,301 detect submarines lurking in 126 00:04:55,368 --> 00:04:57,167 the deep. 127 00:05:01,898 --> 00:05:03,629 The system works by pumping 128 00:05:03,697 --> 00:05:06,461 sound waves through the water. 129 00:05:06,529 --> 00:05:08,160 The waves bounce off solid 130 00:05:08,261 --> 00:05:09,893 objects and are reflected back 131 00:05:09,961 --> 00:05:12,691 to a detector. By measuring 132 00:05:12,725 --> 00:05:13,791 the time it takes for the 133 00:05:13,891 --> 00:05:14,890 sound waves to bounce 134 00:05:14,958 --> 00:05:16,988 back, scientists realized they 135 00:05:17,056 --> 00:05:18,222 could build a remarkably 136 00:05:18,256 --> 00:05:19,687 accurate picture of the world 137 00:05:19,788 --> 00:05:21,619 beneath the waves. 138 00:05:21,687 --> 00:05:22,852 >> The world's major navies 139 00:05:22,886 --> 00:05:24,051 spend a lot of time and effort 140 00:05:24,119 --> 00:05:25,784 developing submarine hunting 141 00:05:25,852 --> 00:05:28,582 technology, then the 142 00:05:28,683 --> 00:05:29,848 hydrographers discover that 143 00:05:29,915 --> 00:05:31,581 you can use this to chart the 144 00:05:31,649 --> 00:05:33,213 bottom of the sea and it's an 145 00:05:33,281 --> 00:05:34,646 awful lot cheaper and easier 146 00:05:34,680 --> 00:05:35,845 than using large numbers of 147 00:05:35,912 --> 00:05:37,844 sailors pulling on ropes. 148 00:05:41,908 --> 00:05:44,274 >> In 1951, a British Navy 149 00:05:44,308 --> 00:05:45,640 research ship returned to the 150 00:05:45,706 --> 00:05:46,939 deep hole found by the 151 00:05:47,006 --> 00:05:50,570 Challenger expedition. 152 00:05:50,638 --> 00:05:52,636 But, this time, they were 153 00:05:52,702 --> 00:05:54,268 armed with sophisticated new 154 00:05:54,335 --> 00:05:55,734 sonar equipment. 155 00:05:59,266 --> 00:06:01,896 And the results were amazing. 156 00:06:03,364 --> 00:06:05,161 Detailed sonar maps revealed 157 00:06:05,263 --> 00:06:06,361 that the deep hole in the 158 00:06:06,428 --> 00:06:08,059 Pacific Ocean floor isn't a 159 00:06:08,160 --> 00:06:10,058 hole at all, but part of a 160 00:06:10,159 --> 00:06:12,224 massive trench, 30 times 161 00:06:12,259 --> 00:06:13,789 deeper than the Empire State 162 00:06:13,890 --> 00:06:15,788 Building is high. 163 00:06:18,521 --> 00:06:20,286 It runs twice the length of 164 00:06:20,320 --> 00:06:22,918 California, 1,500 miles from 165 00:06:22,952 --> 00:06:24,750 the southeast of Guam to the 166 00:06:24,784 --> 00:06:26,183 northwest of the Mariana 167 00:06:26,217 --> 00:06:28,048 Islands. 168 00:06:30,315 --> 00:06:31,646 >> People were probably 169 00:06:31,680 --> 00:06:32,912 astounded by what they were 170 00:06:32,946 --> 00:06:34,578 seeing, because, clearly, the 171 00:06:34,646 --> 00:06:35,911 ocean floor had enormous 172 00:06:35,945 --> 00:06:37,710 changes in relief. It was very 173 00:06:37,744 --> 00:06:39,076 mountainous in some places, 174 00:06:39,110 --> 00:06:40,108 had great deeps in other 175 00:06:40,209 --> 00:06:43,373 places. To a geologist, this 176 00:06:43,474 --> 00:06:45,805 would be extremely exciting. 177 00:06:45,906 --> 00:06:47,604 Even within the trench itself, 178 00:06:47,638 --> 00:06:48,704 there are remarkable 179 00:06:48,738 --> 00:06:51,969 variations. At its southern 180 00:06:52,003 --> 00:06:53,901 end lies the greatest surprise 181 00:06:53,968 --> 00:06:54,900 of all. 182 00:06:57,132 --> 00:06:58,631 The sea floor drops down 183 00:06:58,699 --> 00:07:00,396 another two miles to its 184 00:07:00,431 --> 00:07:02,796 lowest point, a staggering 185 00:07:02,896 --> 00:07:05,328 seven miles beneath the waves. 186 00:07:07,961 --> 00:07:09,592 Scientists had discovered the 187 00:07:09,693 --> 00:07:12,424 deepest part of the oceans. 188 00:07:12,490 --> 00:07:14,555 Even today, it is the lowest 189 00:07:14,590 --> 00:07:17,020 known point on the planet. 190 00:07:18,754 --> 00:07:19,953 They named this part of the 191 00:07:20,020 --> 00:07:21,952 trench the Challenger Deep, in 192 00:07:22,018 --> 00:07:23,017 honor of the ship that 193 00:07:23,118 --> 00:07:24,649 discovered it. 194 00:07:24,717 --> 00:07:26,182 >> To get a sense of just how 195 00:07:26,217 --> 00:07:28,847 deep trenches are, if we take 196 00:07:28,915 --> 00:07:30,713 the heig 197 00:07:30,747 --> 00:07:32,179 we would still have about a 198 00:07:32,213 --> 00:07:34,177 mile of water above us before 199 00:07:34,212 --> 00:07:36,476 we get to the ocean surface. 200 00:07:38,109 --> 00:07:39,708 >> But how the Marianas Trench 201 00:07:39,742 --> 00:07:42,340 was formed remained a mystery. 202 00:07:43,806 --> 00:07:45,371 Investigators decided the best 203 00:07:45,439 --> 00:07:46,970 way to find the answer was to 204 00:07:47,004 --> 00:07:48,169 dive to the bottom of the 205 00:07:48,270 --> 00:07:53,533 trench, to see for themselves 206 00:07:53,601 --> 00:07:54,799 the lowest point on the 207 00:07:54,867 --> 00:07:58,331 planet, the Challenger Deep. 208 00:07:58,431 --> 00:07:59,530 But they faced a major 209 00:07:59,598 --> 00:08:02,795 problem. At the bottom of the 210 00:08:02,862 --> 00:08:04,061 trench, they would have to 211 00:08:04,128 --> 00:08:05,127 contend with pressure a 212 00:08:05,228 --> 00:08:06,659 thousand times stronger than 213 00:08:06,693 --> 00:08:08,958 at the surface, that's the 214 00:08:09,059 --> 00:08:10,490 equivalent of being squeezed 215 00:08:10,558 --> 00:08:12,223 on all sides by the weight of 216 00:08:12,291 --> 00:08:14,655 50 jumbo jets. 217 00:08:17,921 --> 00:08:19,219 To demonstrate the effects of 218 00:08:19,287 --> 00:08:20,751 such pressure, scientists 219 00:08:20,818 --> 00:08:23,184 use a dummy head. 220 00:08:23,218 --> 00:08:24,116 >> Today, what we are going 221 00:08:24,217 --> 00:08:26,282 to do is actually put one of 222 00:08:26,383 --> 00:08:28,613 these Styrofoam wig heads in 223 00:08:28,648 --> 00:08:31,645 the, uh, pressure chamber and 224 00:08:31,746 --> 00:08:33,510 expose it to the, uh, pressure 225 00:08:33,545 --> 00:08:35,076 we would see in the Marianas 226 00:08:35,144 --> 00:08:38,074 Trench. That's about 16,000 227 00:08:38,176 --> 00:08:40,340 psi. 228 00:08:40,408 --> 00:08:41,439 >> A human skull would be 229 00:08:41,541 --> 00:08:43,172 crushed to a pulp, but the 230 00:08:43,273 --> 00:08:44,604 rubbery head will only have 231 00:08:44,639 --> 00:08:48,235 all the air squeezed out. 232 00:08:50,335 --> 00:08:52,866 >> Wow, the head's smaller. 233 00:08:52,934 --> 00:08:55,198 Here's what the original size 234 00:08:55,232 --> 00:08:58,230 was, just for comparison. 235 00:08:58,298 --> 00:08:58,962 [LAUGHS] 236 00:08:59,063 --> 00:09:01,495 Quite dramatic! Pretty stark 237 00:09:01,562 --> 00:09:03,660 difference between, uh, 238 00:09:03,694 --> 00:09:04,593 something that hasn't been 239 00:09:04,661 --> 00:09:06,092 seven miles deep in the ocean 240 00:09:06,126 --> 00:09:07,324 and something that has. 241 00:09:07,392 --> 00:09:08,757 Glad I'm not going there. 242 00:09:08,825 --> 00:09:10,556 [BOTH LAUGH] 243 00:09:10,590 --> 00:09:12,122 At the Mariana Trench, human 244 00:09:12,223 --> 00:09:14,721 life is impossible, we're not 245 00:09:14,755 --> 00:09:17,119 equipped to resist those kinds 246 00:09:17,187 --> 00:09:20,017 of pressures, and so it's 247 00:09:20,118 --> 00:09:21,750 necessary to protect humans 248 00:09:21,818 --> 00:09:22,883 from that type of an 249 00:09:22,917 --> 00:09:23,882 environment. 250 00:09:25,815 --> 00:09:27,147 >> The challenge to engineers 251 00:09:27,181 --> 00:09:29,346 was how to accomplish this. 252 00:09:30,713 --> 00:09:33,077 In 1953, Swiss scientist 253 00:09:33,145 --> 00:09:34,809 Auguste Piccard designed the 254 00:09:34,877 --> 00:09:37,708 Trieste, a pioneering vehicle 255 00:09:37,809 --> 00:09:39,040 that could withstand the 256 00:09:39,075 --> 00:09:40,806 crushing pressures. 257 00:09:45,971 --> 00:09:47,568 The submersible was dominated 258 00:09:47,603 --> 00:09:49,968 by a 50 foot long hull, filled 259 00:09:50,034 --> 00:09:51,766 with light aviation gasoline 260 00:09:51,834 --> 00:09:53,332 and lead weights to control 261 00:09:53,399 --> 00:09:56,396 buoyancy. Slung underneath it 262 00:09:56,464 --> 00:09:58,230 was a tiny six foot spherical 263 00:09:58,296 --> 00:10:00,394 cabin with five inch thick 264 00:10:00,496 --> 00:10:02,826 steel walls. 265 00:10:07,258 --> 00:10:08,823 Finally, after seven years of 266 00:10:08,891 --> 00:10:10,655 modifications and manned test 267 00:10:10,723 --> 00:10:12,021 dives no deeper than three and 268 00:10:12,089 --> 00:10:14,453 a half miles, the Trieste was 269 00:10:14,521 --> 00:10:16,019 ready to attempt the seven 270 00:10:16,054 --> 00:10:17,252 miles to the bottom of the 271 00:10:17,286 --> 00:10:20,649 trench. The commander of this 272 00:10:20,717 --> 00:10:22,416 perilous undertaking was US 273 00:10:22,450 --> 00:10:23,914 Navy Lieutenant and deep sea 274 00:10:23,982 --> 00:10:26,047 explorer Don Walsh. 275 00:10:27,180 --> 00:10:28,612 >> I know the astronauts that 276 00:10:28,713 --> 00:10:29,711 go through this all the time. 277 00:10:29,812 --> 00:10:30,611 "Why do you have to be there? 278 00:10:30,679 --> 00:10:31,610 Why can't we just put up a 279 00:10:31,711 --> 00:10:34,075 robot to do things?" You've 280 00:10:34,143 --> 00:10:35,408 got to be there because that's 281 00:10:35,442 --> 00:10:37,940 what we do. 282 00:10:37,974 --> 00:10:39,339 >> Only a few officers and 283 00:10:39,373 --> 00:10:40,705 scientists knew about the 284 00:10:40,773 --> 00:10:42,038 risky mission, which was 285 00:10:42,139 --> 00:10:44,236 launched in January 1960 from 286 00:10:44,304 --> 00:10:45,735 the western Pacific island of 287 00:10:45,770 --> 00:10:48,468 Guam. 288 00:10:48,502 --> 00:10:50,400 >> Guam in those days was kind 289 00:10:50,501 --> 00:10:51,932 of a backwater, it was just 290 00:10:52,033 --> 00:10:53,198 right for us because we were 291 00:10:53,232 --> 00:10:55,197 trying to do this project sort 292 00:10:55,264 --> 00:10:57,396 of out of sight, because we 293 00:10:57,497 --> 00:10:58,462 weren't too sure it was gonna 294 00:10:58,496 --> 00:11:01,027 work. The navy just didn't 295 00:11:01,095 --> 00:11:02,259 want to be embarrassed by a 296 00:11:02,360 --> 00:11:05,058 failed science spectacular. 297 00:11:07,591 --> 00:11:08,889 >> Accompanying Walsh was the 298 00:11:08,957 --> 00:11:10,688 son of the Trieste's designer, 299 00:11:10,756 --> 00:11:12,221 engineer and oceanographer 300 00:11:12,255 --> 00:11:15,585 Jacques Piccard. The two men 301 00:11:15,686 --> 00:11:16,784 would spend the next nine 302 00:11:16,852 --> 00:11:18,484 hours squeezed inside the 303 00:11:18,585 --> 00:11:21,282 cramped sphere. 304 00:11:21,316 --> 00:11:23,281 >> And we had, erm, 20 cubic 305 00:11:23,315 --> 00:11:25,213 feet of space inside, that's 306 00:11:25,314 --> 00:11:26,046 about the same as a 307 00:11:26,114 --> 00:11:28,812 household refrigerator, and 308 00:11:28,846 --> 00:11:30,310 the temperature was almost 309 00:11:30,378 --> 00:11:32,942 that cold inside. It was a 310 00:11:33,010 --> 00:11:34,108 drama. 311 00:11:36,908 --> 00:11:37,939 >> The story of how the 312 00:11:38,007 --> 00:11:39,905 Marianas Trench came to be is 313 00:11:40,006 --> 00:11:43,536 beginning to take shape. 314 00:11:43,603 --> 00:11:46,101 In 1874, British surveyors 315 00:11:46,169 --> 00:11:47,434 were the first to discover 316 00:11:47,468 --> 00:11:49,266 a five mile deep hole in the 317 00:11:49,367 --> 00:11:52,731 ocean. 75 years later, sonar 318 00:11:52,799 --> 00:11:54,064 mapping revealed the hole to 319 00:11:54,131 --> 00:11:56,328 be a vast, 1,500-mile long 320 00:11:56,430 --> 00:11:58,894 trench, with the deepest part 321 00:11:58,961 --> 00:12:00,627 seven miles beneath the 322 00:12:00,694 --> 00:12:03,892 surface waves of the Pacific. 323 00:12:03,958 --> 00:12:05,490 To gather further evidence, 324 00:12:05,525 --> 00:12:07,289 two courageous men were about 325 00:12:07,323 --> 00:12:08,389 to undertake the most 326 00:12:08,423 --> 00:12:11,387 dangerous dive in history. 327 00:12:11,422 --> 00:12:13,019 They would venture into the 328 00:12:13,054 --> 00:12:15,818 abyss and go to the bottom of 329 00:12:15,852 --> 00:12:18,849 the Marianas Trench. 330 00:12:21,316 --> 00:12:23,147 The Marianas Trench is one of 331 00:12:23,215 --> 00:12:24,847 the most remote, inhospitable 332 00:12:24,948 --> 00:12:26,879 places on Earth. 333 00:12:30,045 --> 00:12:32,775 In January 1960, two deep sea 334 00:12:32,843 --> 00:12:34,640 explorers, Don Walsh and 335 00:12:34,675 --> 00:12:37,139 Jacques Piccard, plunged into 336 00:12:37,207 --> 00:12:38,672 its depths on board the 337 00:12:38,740 --> 00:12:41,037 submersible, the Trieste. 338 00:12:47,534 --> 00:12:49,299 At a speed of just three miles 339 00:12:49,367 --> 00:12:51,032 per hour, they began their 340 00:12:51,100 --> 00:12:52,997 slow descent into the twilight 341 00:12:53,064 --> 00:12:54,463 zone. 342 00:12:57,096 --> 00:12:59,194 By 3,000 feet, the darkness 343 00:12:59,261 --> 00:13:02,325 was total. The only 344 00:13:02,360 --> 00:13:03,691 illumination was from the 345 00:13:03,726 --> 00:13:05,790 Trieste's powerful lights. 346 00:13:08,456 --> 00:13:09,154 >> At the depths we were 347 00:13:09,222 --> 00:13:10,354 operating at, it was always 348 00:13:10,421 --> 00:13:12,686 black. The only thing that lit 349 00:13:12,721 --> 00:13:13,985 up the abyss was the 350 00:13:14,053 --> 00:13:16,683 bioluminescence from animals 351 00:13:16,751 --> 00:13:20,581 and plankton. Like fireflies, 352 00:13:20,682 --> 00:13:21,947 they carry their own light 353 00:13:22,048 --> 00:13:24,779 sources with them. 354 00:13:24,880 --> 00:13:26,411 >> Encased in their five-inch 355 00:13:26,479 --> 00:13:28,377 thick steel sphere, Walsh and 356 00:13:28,411 --> 00:13:29,943 Piccard quickly passed their 357 00:13:30,043 --> 00:13:31,942 test dive record of 18,000 358 00:13:32,009 --> 00:13:35,107 feet. Everything appeared to 359 00:13:35,207 --> 00:13:38,838 be going to plan. At the rear 360 00:13:38,906 --> 00:13:40,303 of the cabin, the crew were 361 00:13:40,371 --> 00:13:41,936 protected by a double layer of 362 00:13:42,004 --> 00:13:44,201 glass. But, two hours into the 363 00:13:44,269 --> 00:13:47,100 dive, the outer pane cracked. 364 00:13:50,465 --> 00:13:52,097 >> We, um, had a great big 365 00:13:52,165 --> 00:13:53,996 bang. We didn't know what it 366 00:13:54,064 --> 00:13:55,362 was. We were at about 20,000 367 00:13:55,430 --> 00:13:57,161 feet, and we looked around and 368 00:13:57,262 --> 00:13:59,959 checked everything, 369 00:13:59,994 --> 00:14:01,525 >> Every square inch of their 370 00:14:01,592 --> 00:14:02,957 tiny life-supporting capsule 371 00:14:02,992 --> 00:14:04,790 was fighting back eight tons 372 00:14:04,891 --> 00:14:08,221 of pressure. With the outer 373 00:14:08,256 --> 00:14:10,253 pane broken, the only thing 374 00:14:10,321 --> 00:14:11,619 between the men and instant 375 00:14:11,687 --> 00:14:13,218 death was a single pane of 376 00:14:13,320 --> 00:14:14,217 glass. 377 00:14:14,319 --> 00:14:15,318 >> If the inner window had 378 00:14:15,418 --> 00:14:17,150 cracked, erm, we would have 379 00:14:17,217 --> 00:14:20,148 been instantly dead, maybe 380 00:14:20,215 --> 00:14:22,946 even before we knew it. 381 00:14:23,047 --> 00:14:24,478 >> But, incredibly, the inner 382 00:14:24,579 --> 00:14:27,044 pane remained watertight. 383 00:14:27,111 --> 00:14:28,543 Walsh and Piccard decided to 384 00:14:28,577 --> 00:14:32,474 continue the descent. 385 00:14:32,574 --> 00:14:34,373 After a tense, claustrophobic 386 00:14:34,473 --> 00:14:36,372 four hours and 48 minutes, 387 00:14:36,472 --> 00:14:37,638 they approached the bottom of 388 00:14:37,705 --> 00:14:39,337 the trench, only to be 389 00:14:39,371 --> 00:14:40,836 startled by movement on the 390 00:14:40,903 --> 00:14:43,101 sea floor. 391 00:14:43,169 --> 00:14:45,100 >> Just before we landed, we 392 00:14:45,168 --> 00:14:47,898 saw a flatfish about a foot 393 00:14:47,999 --> 00:14:50,264 long, and that's a 394 00:14:50,332 --> 00:14:51,996 bottom-dwelling fish, so if 395 00:14:52,064 --> 00:14:54,062 you see one there are others, 396 00:14:55,595 --> 00:14:57,426 >> Nobody expected to see life 397 00:14:57,494 --> 00:14:59,525 at these crushing depths, but 398 00:14:59,593 --> 00:15:00,891 it meant the explorers had 399 00:15:00,959 --> 00:15:06,521 reached their goal, the very 400 00:15:06,589 --> 00:15:08,953 bottom of the Marianas Trench. 401 00:15:10,320 --> 00:15:11,419 The depth gauge, with a 402 00:15:11,486 --> 00:15:14,317 reading of 35,800 feet, nearly 403 00:15:14,385 --> 00:15:16,849 seven miles below the surface, 404 00:15:16,916 --> 00:15:19,681 confirmed the sonar findings. 405 00:15:24,579 --> 00:15:26,111 Squeezed inside their bubble 406 00:15:26,177 --> 00:15:27,643 of breathable air, the two 407 00:15:27,744 --> 00:15:29,009 explorers were closer to the 408 00:15:29,110 --> 00:15:30,475 Earth's centre than man had 409 00:15:30,542 --> 00:15:32,474 ever been. 410 00:15:32,540 --> 00:15:35,904 We took a self-portrait, 411 00:15:35,972 --> 00:15:37,170 that's the picture that you 412 00:15:37,238 --> 00:15:38,737 see. We said we were going 413 00:15:38,804 --> 00:15:40,602 to do it, and we did it. 414 00:15:43,168 --> 00:15:44,166 >> But there was work to be 415 00:15:44,268 --> 00:15:47,132 done. Walsh and Piccard wanted 416 00:15:47,166 --> 00:15:48,764 to make detailed observations 417 00:15:48,798 --> 00:15:50,596 of the enormous trench. 418 00:15:52,429 --> 00:15:53,961 Unfortunately, the Trieste 419 00:15:54,062 --> 00:15:55,593 stirred up a cloud of fine, 420 00:15:55,661 --> 00:15:57,059 powdery sediment from the sea 421 00:15:57,160 --> 00:15:58,492 floor that obscured their 422 00:15:58,560 --> 00:15:59,524 view. 423 00:16:01,591 --> 00:16:02,689 >> WALSH: It was like being in 424 00:16:02,757 --> 00:16:04,289 a bowl of milk at that point. 425 00:16:04,323 --> 00:16:05,754 So, realizing that we weren't 426 00:16:05,822 --> 00:16:07,686 gonna see anything, we decided 427 00:16:07,754 --> 00:16:08,686 to go on back up to the 428 00:16:08,754 --> 00:16:10,385 surface. 429 00:16:10,453 --> 00:16:11,185 >> ANNOUNCER: Off the island 430 00:16:11,219 --> 00:16:13,217 of Guam, the Trieste surfaces 431 00:16:13,285 --> 00:16:14,116 after a descent into the 432 00:16:14,184 --> 00:16:16,082 Marianas Trench. 433 00:16:16,116 --> 00:16:17,748 >> After nine grueling hours 434 00:16:17,848 --> 00:16:19,614 underwater, Walsh and Piccard 435 00:16:19,648 --> 00:16:20,846 returned to the surface on 436 00:16:20,914 --> 00:16:24,344 January 23rd 1960 and 437 00:16:24,378 --> 00:16:25,610 officially entered the record 438 00:16:25,644 --> 00:16:27,542 books for the deepest dive of 439 00:16:27,610 --> 00:16:31,007 all time. To this day, their 440 00:16:31,075 --> 00:16:32,806 extraordinary feat has never 441 00:16:32,907 --> 00:16:33,805 been repeated. 442 00:16:37,338 --> 00:16:40,602 The mission was a success, but 443 00:16:40,669 --> 00:16:43,234 the mystery remained. 444 00:16:43,301 --> 00:16:44,966 Geologists still didn't 445 00:16:45,033 --> 00:16:46,332 understand what could have 446 00:16:46,399 --> 00:16:49,030 formed the immense trench. 447 00:16:50,130 --> 00:16:51,229 And if they couldn't find the 448 00:16:51,296 --> 00:16:53,261 answer inside the trench, 449 00:16:53,295 --> 00:16:54,260 they would have to look 450 00:16:54,294 --> 00:16:55,993 elsewhere. 451 00:16:58,559 --> 00:16:59,724 Perhaps there was something, 452 00:16:59,792 --> 00:17:01,656 somewhere, on the ocean floor 453 00:17:01,657 --> 00:17:02,689 that might explain the 454 00:17:02,756 --> 00:17:04,688 trench's origins. 455 00:17:08,486 --> 00:17:09,851 Throughout the '50s and '60s, 456 00:17:09,919 --> 00:17:11,417 a team of geologists led by 457 00:17:11,484 --> 00:17:12,849 Princeton's Harry Hess 458 00:17:12,917 --> 00:17:14,815 compiled sonar data from all 459 00:17:14,849 --> 00:17:16,847 of the world's oceans. 460 00:17:20,646 --> 00:17:21,711 It was as though they had 461 00:17:21,745 --> 00:17:23,643 pulled out a giant plug, to 462 00:17:23,744 --> 00:17:25,542 drain away all the water, and 463 00:17:25,577 --> 00:17:29,107 expose the ocean floor. 464 00:17:29,175 --> 00:17:30,207 Their maps revealed that the 465 00:17:30,274 --> 00:17:32,272 Marianas Trench is just a tiny 466 00:17:32,373 --> 00:17:33,804 fraction of a network of 467 00:17:33,905 --> 00:17:35,903 enormous underwater canyons 468 00:17:36,004 --> 00:17:37,269 stretching right around the 469 00:17:37,337 --> 00:17:41,134 planet. But that wasn't all. 470 00:17:41,168 --> 00:17:42,166 Running parallel to the 471 00:17:42,234 --> 00:17:43,532 trench, on the other side of 472 00:17:43,600 --> 00:17:45,165 the Pacific, the maps showed a 473 00:17:45,265 --> 00:17:46,630 giant underwater mountain 474 00:17:46,698 --> 00:17:50,262 range, the East Pacific Ridge. 475 00:17:50,329 --> 00:17:52,227 And this too is part of a 476 00:17:52,328 --> 00:17:54,859 global network, a 40,000 mile 477 00:17:54,960 --> 00:17:56,691 long chain of mountain ranges 478 00:17:56,759 --> 00:17:58,057 that ring the globe like the 479 00:17:58,125 --> 00:18:00,423 seams of a baseball, to make 480 00:18:00,490 --> 00:18:02,389 the largest geological feature 481 00:18:02,422 --> 00:18:03,687 on Earth. 482 00:18:06,121 --> 00:18:07,486 It was a major development in 483 00:18:07,553 --> 00:18:09,218 the investigation, one that 484 00:18:09,319 --> 00:18:10,917 scientists hoped might explain 485 00:18:10,951 --> 00:18:12,715 the trench's formation. 486 00:18:15,382 --> 00:18:17,213 The next step was clear. 487 00:18:17,281 --> 00:18:18,612 Investigators needed to 488 00:18:18,647 --> 00:18:19,912 understand whether there was a 489 00:18:20,013 --> 00:18:21,544 connection between the trench 490 00:18:21,611 --> 00:18:23,876 and the East Pacific Ridge. 491 00:18:32,438 --> 00:18:34,137 The breakthrough came from the 492 00:18:34,172 --> 00:18:38,168 unlikeliest of sources. During 493 00:18:38,235 --> 00:18:40,033 the Cold War, the US built a 494 00:18:40,067 --> 00:18:41,799 vast network of underground 495 00:18:41,867 --> 00:18:43,698 seismometers to pick up atomic 496 00:18:43,766 --> 00:18:45,863 bomb testing around the world. 497 00:18:48,596 --> 00:18:49,595 Inadvertently, the 498 00:18:49,695 --> 00:18:51,394 seismometers also detected 499 00:18:51,428 --> 00:18:52,426 naturally occurring 500 00:18:52,494 --> 00:18:56,757 earthquakes. When geologists 501 00:18:56,858 --> 00:18:58,323 plotted these on a map, a 502 00:18:58,391 --> 00:19:00,389 pattern emerged. 503 00:19:03,288 --> 00:19:05,286 The earthquakes were clustered 504 00:19:05,387 --> 00:19:07,218 along the ocean's ridges and 505 00:19:07,286 --> 00:19:09,750 trenches. It was a discovery 506 00:19:09,818 --> 00:19:10,749 that transformed our 507 00:19:10,850 --> 00:19:13,648 understanding of the Earth. 508 00:19:13,749 --> 00:19:15,280 Geologists realized the 509 00:19:15,381 --> 00:19:16,313 friction that cause 510 00:19:16,348 --> 00:19:17,812 earthquakes comes from 511 00:19:17,880 --> 00:19:18,978 movements that must be 512 00:19:19,045 --> 00:19:20,344 occurring deep beneath the 513 00:19:20,411 --> 00:19:22,676 ridges and trenches. 514 00:19:22,744 --> 00:19:23,876 >> With this great investment 515 00:19:23,943 --> 00:19:25,774 in seismology, it became 516 00:19:25,842 --> 00:19:27,673 possible to locate very 517 00:19:27,741 --> 00:19:29,305 precisely where earthquakes 518 00:19:29,406 --> 00:19:32,037 had occurred. And it was these 519 00:19:32,105 --> 00:19:33,570 things, the precise location, 520 00:19:33,670 --> 00:19:35,735 the depth and the motion that 521 00:19:35,769 --> 00:19:37,001 really gave the outlines of 522 00:19:37,035 --> 00:19:40,199 plate tectonics. 523 00:19:40,267 --> 00:19:41,532 >> It was the birth of an 524 00:19:41,566 --> 00:19:45,463 extraordinary new theory. The 525 00:19:45,564 --> 00:19:47,095 solid layer of rock, the 526 00:19:47,196 --> 00:19:48,795 crust, on which the land and 527 00:19:48,829 --> 00:19:50,926 ocean sits, is broken up into 528 00:19:50,994 --> 00:19:53,259 a series of vast slabs, that 529 00:19:53,360 --> 00:19:55,091 geologists call tectonic 530 00:19:55,192 --> 00:19:57,690 plates. It's these plates that 531 00:19:57,724 --> 00:20:00,088 are moving, grinding past each 532 00:20:00,156 --> 00:20:01,887 other, and triggering 533 00:20:01,988 --> 00:20:03,520 earthquakes. 534 00:20:06,785 --> 00:20:08,051 The underwater ridges and 535 00:20:08,151 --> 00:20:10,116 trenches sit on the boundaries 536 00:20:10,150 --> 00:20:12,581 between tectonic plates. 537 00:20:12,615 --> 00:20:14,513 The East Pacific Ridge and the 538 00:20:14,614 --> 00:20:16,313 Marianas Trench lie on 539 00:20:16,413 --> 00:20:18,011 opposite edges of the Pacific 540 00:20:18,046 --> 00:20:19,411 Plate. 541 00:20:21,044 --> 00:20:22,209 The journey to discover what 542 00:20:22,310 --> 00:20:23,842 formed the Marianas Trench is 543 00:20:23,943 --> 00:20:25,141 accumulating additional 544 00:20:25,209 --> 00:20:28,406 evidence. The Trieste dived to 545 00:20:28,473 --> 00:20:30,771 the bottom of the trench, 546 00:20:30,839 --> 00:20:33,002 and confirmed that it is the 547 00:20:33,037 --> 00:20:35,801 deepest point on the planet. 548 00:20:35,836 --> 00:20:37,433 Sonar maps then revealed the 549 00:20:37,468 --> 00:20:39,100 East Pacific Ocean Ridge, 550 00:20:39,201 --> 00:20:40,532 running parallel to the 551 00:20:40,567 --> 00:20:44,696 trench. To solve the mystery 552 00:20:44,730 --> 00:20:46,162 of the Marianas Trench, 553 00:20:46,197 --> 00:20:47,761 investigators needed to find 554 00:20:47,795 --> 00:20:49,494 out exactly what was happening 555 00:20:49,594 --> 00:20:51,759 at the East Pacific Ridge, and 556 00:20:51,827 --> 00:20:53,491 that meant exploring these 557 00:20:53,559 --> 00:20:56,689 vast mountains, 8,000 feet 558 00:20:56,757 --> 00:20:58,137 underwater. 559 00:21:04,572 --> 00:21:05,870 The pieces of the Marianas 560 00:21:05,938 --> 00:21:07,303 Trench puzzle are falling into 561 00:21:07,403 --> 00:21:08,668 place with the knowledge that 562 00:21:08,769 --> 00:21:10,567 it lies on the western edge of 563 00:21:10,668 --> 00:21:12,933 the Pacific tectonic plate. 564 00:21:15,299 --> 00:21:16,464 On the opposite side of the 565 00:21:16,565 --> 00:21:18,097 plate lies the East Pacific 566 00:21:18,164 --> 00:21:20,195 Ocean Ridge, part of an! 567 00:21:20,296 --> 00:21:22,260 enormous chain of underwater 568 00:21:22,295 --> 00:21:23,893 mountain ranges that ring the 569 00:21:23,928 --> 00:21:25,726 globe to create the largest 570 00:21:25,760 --> 00:21:29,190 geological feature on Earth. 571 00:21:29,257 --> 00:21:30,823 Scientists had a hunch that 572 00:21:30,890 --> 00:21:32,421 this colossal ridge might help 573 00:21:32,456 --> 00:21:34,220 explain how the trench was 574 00:21:34,254 --> 00:21:38,185 formed. And they found a major 575 00:21:38,219 --> 00:21:40,683 clue halfway round the globe, 576 00:21:40,751 --> 00:21:42,216 where the ridge passed beneath 577 00:21:42,317 --> 00:21:43,482 the middle of the Atlantic 578 00:21:43,583 --> 00:21:44,815 Ocean. 579 00:21:48,213 --> 00:21:50,012 During the Cold War, the US 580 00:21:50,046 --> 00:21:51,811 Navy developed a new technique 581 00:21:51,845 --> 00:21:55,109 to spot Soviet submarines. 582 00:21:55,177 --> 00:21:56,607 They scanned the seas with a 583 00:21:56,642 --> 00:21:59,106 tool called MAD, a magnetic 584 00:21:59,174 --> 00:22:01,072 anomaly detector, which could 585 00:22:01,173 --> 00:22:02,904 pinpoint steel hulls lurking 586 00:22:03,005 --> 00:22:07,002 in the deep. But they stumbled 587 00:22:07,070 --> 00:22:11,232 across something else. Running 588 00:22:11,267 --> 00:22:12,699 parallel on either side of the 589 00:22:12,766 --> 00:22:14,397 ridge, they found strange 590 00:22:14,432 --> 00:22:16,330 stripes of magnetic rocks, 591 00:22:16,397 --> 00:22:17,696 alternating positive and 592 00:22:17,763 --> 00:22:19,494 negative away from the ridge's 593 00:22:19,595 --> 00:22:21,393 peak. 594 00:22:21,428 --> 00:22:23,959 Here's the Mid-Atlantic Ridge 595 00:22:24,026 --> 00:22:25,224 coming down through here. 596 00:22:25,326 --> 00:22:27,223 Almost perfectly symmetric on 597 00:22:27,325 --> 00:22:28,957 either side of that are these 598 00:22:29,023 --> 00:22:31,288 white and black stripes, these 599 00:22:31,323 --> 00:22:32,954 have often been called zebra 600 00:22:33,021 --> 00:22:34,486 stripes. 601 00:22:36,086 --> 00:22:37,584 >> Geologists know that the 602 00:22:37,652 --> 00:22:39,383 Earth is like a giant magnet 603 00:22:39,484 --> 00:22:42,015 with a north and a south pole. 604 00:22:42,116 --> 00:22:43,747 But the magnetic poles aren't 605 00:22:43,848 --> 00:22:46,912 fixed. Every 300,000 years or 606 00:22:46,980 --> 00:22:48,278 so, the magnetic field 607 00:22:48,346 --> 00:22:49,911 suddenly flips 180 degrees. 608 00:22:54,276 --> 00:22:55,808 When the field flips, a 609 00:22:55,908 --> 00:22:57,273 compass that was previously 610 00:22:57,341 --> 00:22:59,072 pointing north will swing to 611 00:22:59,173 --> 00:23:00,805 the south. 612 00:23:00,873 --> 00:23:02,437 >> This reversing of the 613 00:23:02,505 --> 00:23:05,069 Earth's magnetic field is a 614 00:23:05,137 --> 00:23:06,535 very interesting and exciting 615 00:23:06,603 --> 00:23:08,167 but very puzzling phenomenon 616 00:23:08,235 --> 00:23:10,066 for a geophysicist to explain. 617 00:23:11,966 --> 00:23:13,331 >> Scientists think this 618 00:23:13,399 --> 00:23:15,030 reversal explains the stripes 619 00:23:15,064 --> 00:23:16,496 either side of the ocean 620 00:23:16,597 --> 00:23:21,294 ridge. In the 1960s, 621 00:23:21,327 --> 00:23:22,759 geologists discovered that 622 00:23:22,860 --> 00:23:24,925 molten volcanic rock, known as 623 00:23:24,959 --> 00:23:26,556 magma, swelled up from deep 624 00:23:26,591 --> 00:23:28,123 underground to create the 625 00:23:28,190 --> 00:23:29,455 ridges in the Atlantic and 626 00:23:29,490 --> 00:23:30,921 Pacific. 627 00:23:32,854 --> 00:23:34,719 As magma wells up between the 628 00:23:34,753 --> 00:23:36,918 tectonic plates, it pushes the 629 00:23:36,985 --> 00:23:39,017 sea floor up, and forms the 630 00:23:39,084 --> 00:23:40,715 colossal mid-ocean ridge, 631 00:23:40,783 --> 00:23:42,981 thousands of feet high. 632 00:23:46,480 --> 00:23:47,845 When the rock is hot and 633 00:23:47,879 --> 00:23:49,677 molten, its magnetic minerals 634 00:23:49,778 --> 00:23:51,309 line up with the north-south 635 00:23:51,377 --> 00:23:52,509 direction of the Earth's 636 00:23:52,543 --> 00:23:55,407 magnetic field. As the magma 637 00:23:55,508 --> 00:23:57,373 cools, the minerals are locked 638 00:23:57,407 --> 00:23:59,038 in position. 639 00:24:02,304 --> 00:24:04,302 These rocks act as a permanent 640 00:24:04,370 --> 00:24:05,801 record of the magnetic poles' 641 00:24:05,836 --> 00:24:07,433 location when the rocks were 642 00:24:07,468 --> 00:24:12,564 formed. As more and more magma 643 00:24:12,632 --> 00:24:14,696 is forced up, the old crust is 644 00:24:14,731 --> 00:24:16,162 pushed away from the ridge and 645 00:24:16,229 --> 00:24:17,594 records the reversals in the 646 00:24:17,662 --> 00:24:19,693 Earth's magnetic polarity. 647 00:24:19,794 --> 00:24:20,759 >> If you have reversals of 648 00:24:20,793 --> 00:24:22,392 magnetic polarity, then the 649 00:24:22,426 --> 00:24:23,791 sea floor acts sort of like a 650 00:24:23,858 --> 00:24:25,923 tape recorder and records 651 00:24:26,024 --> 00:24:26,923 these changes in 652 00:24:27,023 --> 00:24:28,256 magnetization, then the 653 00:24:28,290 --> 00:24:30,354 pattern of magnetic stripes 654 00:24:30,421 --> 00:24:33,086 allows people to calculate the 655 00:24:33,153 --> 00:24:34,418 speed at which the plates are 656 00:24:34,453 --> 00:24:35,684 moving apart. 657 00:24:39,250 --> 00:24:40,815 The zebra stripes are proof 658 00:24:40,883 --> 00:24:42,881 that, over time, the sea floor 659 00:24:42,948 --> 00:24:44,246 in both the Atlantic and the 660 00:24:44,313 --> 00:24:45,979 Pacific, is spreading away 661 00:24:46,046 --> 00:24:47,611 from the ridges at a rate of 662 00:24:47,712 --> 00:24:49,877 more than two inches a year. 663 00:24:51,343 --> 00:24:53,041 But geologists needed proof 664 00:24:53,142 --> 00:24:56,772 that magma created the ridge. 665 00:24:56,840 --> 00:24:58,671 If red-hot molten rock is 666 00:24:58,739 --> 00:25:00,004 forming the enormous mountain 667 00:25:00,038 --> 00:25:01,569 range in the Pacific, the 668 00:25:01,637 --> 00:25:02,935 surrounding water should be 669 00:25:03,003 --> 00:25:05,201 warm. 670 00:25:08,133 --> 00:25:10,764 In 1977, a team of scientists 671 00:25:10,832 --> 00:25:12,197 set out to discover whether 672 00:25:12,298 --> 00:25:13,563 this warm water really 673 00:25:13,663 --> 00:25:15,195 existed. 674 00:25:17,428 --> 00:25:19,026 Dudley Foster was the pilot 675 00:25:19,094 --> 00:25:21,258 for these historic dives. 676 00:25:21,292 --> 00:25:22,924 >> It's been an exciting 677 00:25:22,992 --> 00:25:24,790 occupation because you're on 678 00:25:24,891 --> 00:25:26,589 the cutting edge of science, 679 00:25:26,690 --> 00:25:28,021 uh, new discoveries all the 680 00:25:28,056 --> 00:25:31,420 time. Every cruise, there's a 681 00:25:31,486 --> 00:25:32,552 new group of scientists with 682 00:25:32,587 --> 00:25:34,184 new scientific objectives and 683 00:25:34,219 --> 00:25:35,283 there's the exploration and 684 00:25:35,318 --> 00:25:37,849 the discovery and that's 685 00:25:37,950 --> 00:25:39,814 really what puts the thrill in 686 00:25:39,915 --> 00:25:40,848 the job. 687 00:25:46,178 --> 00:25:47,844 >> For weeks, the crew scanned 688 00:25:47,911 --> 00:25:49,475 the undersea mountains without 689 00:25:49,543 --> 00:25:53,107 success. And then, they hit 690 00:25:53,174 --> 00:25:59,437 the jackpot, a bizarre pillar 691 00:25:59,537 --> 00:26:02,701 of rock, spewing hot toxic 692 00:26:02,802 --> 00:26:04,367 gas. 693 00:26:06,967 --> 00:26:08,165 >> And we saw the water was 694 00:26:08,266 --> 00:26:09,698 sort of shimmering, sort of 695 00:26:09,798 --> 00:26:12,130 like, uh, bubbling in a glass 696 00:26:12,231 --> 00:26:14,595 teapot or something. 697 00:26:15,695 --> 00:26:16,860 We stuck the temperature probe 698 00:26:16,961 --> 00:26:19,159 in there and it measured 38, 699 00:26:19,227 --> 00:26:21,025 39 degrees Fahrenheit, which 700 00:26:21,059 --> 00:26:22,590 was really amazing, 'cause 701 00:26:22,691 --> 00:26:24,056 the--the ocean's a huge heat 702 00:26:24,124 --> 00:26:26,388 sink, and so to see something 703 00:26:26,489 --> 00:26:27,854 warm like that was kind of 704 00:26:27,955 --> 00:26:30,120 startling. 705 00:26:30,187 --> 00:26:31,685 >> In these pillars of rock, 706 00:26:31,753 --> 00:26:33,218 the expedition had found the 707 00:26:33,286 --> 00:26:35,283 heat from the magma surging up 708 00:26:35,350 --> 00:26:37,715 from deep inside the Earth. 709 00:26:39,382 --> 00:26:40,814 It wasn't warming the water 710 00:26:40,848 --> 00:26:43,379 evenly along the ridge, it was 711 00:26:43,446 --> 00:26:45,011 channeled up through strange 712 00:26:45,078 --> 00:26:48,442 hydrothermal vents. 713 00:26:48,544 --> 00:26:49,275 >> FOSTER: When you make these 714 00:26:49,342 --> 00:26:50,375 discoveries, you don't know 715 00:26:50,442 --> 00:26:53,706 how significant they are. The 716 00:26:53,773 --> 00:26:56,138 true significance of 'em maybe 717 00:26:56,173 --> 00:26:57,337 takes several years to 718 00:26:57,438 --> 00:26:59,336 appreciate, and this was one 719 00:26:59,437 --> 00:27:01,169 of those times. 720 00:27:03,035 --> 00:27:04,233 >> For the investigation into 721 00:27:04,334 --> 00:27:05,965 the Marianas Trench, these 722 00:27:06,066 --> 00:27:07,532 vents are a decisive piece of 723 00:27:07,599 --> 00:27:09,330 evidence. 724 00:27:11,330 --> 00:27:13,061 They confirm that magma is 725 00:27:13,129 --> 00:27:15,127 continually creating new crust 726 00:27:15,228 --> 00:27:17,126 at the Pacific Ocean Ridge. 727 00:27:18,326 --> 00:27:19,725 And magnetic zebra stripes 728 00:27:19,826 --> 00:27:21,457 prove that old crust is pushed 729 00:27:21,558 --> 00:27:22,990 away from the ridge towards 730 00:27:23,090 --> 00:27:24,555 the other side of the Pacific 731 00:27:24,623 --> 00:27:26,788 Plate, towards the Marianas 732 00:27:26,822 --> 00:27:31,152 Trench. But this presents 733 00:27:31,253 --> 00:27:33,050 scientists with a puzzle. 734 00:27:33,085 --> 00:27:34,783 If new crust is being created 735 00:27:34,884 --> 00:27:36,515 at the ocean ridge, and the 736 00:27:36,582 --> 00:27:38,348 Earth isn't expanding, then 737 00:27:38,414 --> 00:27:39,614 the old crust must be 738 00:27:39,714 --> 00:27:42,311 disappearing somewhere else. 739 00:27:42,346 --> 00:27:43,778 >> The reason that the Earth's 740 00:27:43,845 --> 00:27:45,377 not getting bigger with sea 741 00:27:45,410 --> 00:27:46,510 floor spreading is because the 742 00:27:46,611 --> 00:27:47,876 same amount of sea floor is 743 00:27:47,943 --> 00:27:49,241 being destroyed in the 744 00:27:49,308 --> 00:27:51,306 Pacific. 745 00:27:51,374 --> 00:27:52,572 >> Something in the Pacific 746 00:27:52,640 --> 00:27:54,404 Ocean is devouring the sea 747 00:27:54,506 --> 00:27:57,770 floor. And all the evidence 748 00:27:57,837 --> 00:28:02,900 points to the Marianas Trench. 749 00:28:06,157 --> 00:28:07,489 In the hunt to discover what 750 00:28:07,523 --> 00:28:09,121 formed the Marianas Trench, 751 00:28:09,155 --> 00:28:11,120 scientists now know crust 752 00:28:11,188 --> 00:28:13,052 created at the ocean ridge is 753 00:28:13,120 --> 00:28:15,051 being devoured somewhere and 754 00:28:15,119 --> 00:28:16,683 by something in the Pacific 755 00:28:16,751 --> 00:28:18,049 Ocean. 756 00:28:21,948 --> 00:28:23,480 They suspect the Marianas 757 00:28:23,581 --> 00:28:28,177 Trench is involved. But the 758 00:28:28,211 --> 00:28:29,643 proof would come, not from the 759 00:28:29,744 --> 00:28:34,274 trench, but from these, the 760 00:28:34,342 --> 00:28:36,872 Mariana Islands, a chain of 761 00:28:36,907 --> 00:28:38,638 volcanoes that break through 762 00:28:38,706 --> 00:28:41,403 the ocean's surface 200 miles 763 00:28:41,471 --> 00:28:44,734 west of the trench. Scientists 764 00:28:44,768 --> 00:28:46,233 noticed the island chain 765 00:28:46,301 --> 00:28:47,833 mirrors the trench's exact 766 00:28:47,867 --> 00:28:50,365 shape. This led them to think 767 00:28:50,433 --> 00:28:51,963 the trench was responsible for 768 00:28:51,998 --> 00:28:53,630 the islands' creation. 769 00:28:56,096 --> 00:28:57,328 >> If, uh, you see pictures of 770 00:28:57,362 --> 00:28:58,527 the Marianas Trench, it's 771 00:28:58,594 --> 00:29:00,326 curved, and the line of 772 00:29:00,360 --> 00:29:01,692 volcanoes that it generates is 773 00:29:01,726 --> 00:29:03,424 curved exactly parallel to it, 774 00:29:05,590 --> 00:29:06,989 >> Geologists believe that the 775 00:29:07,056 --> 00:29:08,587 trench formed the volcanoes 776 00:29:08,689 --> 00:29:10,120 via a process called 777 00:29:10,155 --> 00:29:13,951 subduction. Subduction occurs 778 00:29:14,053 --> 00:29:15,583 where two tectonic plates 779 00:29:15,651 --> 00:29:17,915 collide. As they grind past 780 00:29:17,949 --> 00:29:19,415 each other, the heavier plate 781 00:29:19,482 --> 00:29:20,947 is pushed beneath the lighter 782 00:29:21,015 --> 00:29:23,745 plate. The descending plate is 783 00:29:23,846 --> 00:29:25,278 forced down into the Earth's 784 00:29:25,313 --> 00:29:27,210 intensely hot interior, called 785 00:29:27,278 --> 00:29:29,442 the mantle. It takes with it 786 00:29:29,476 --> 00:29:31,008 water and sediment built up 787 00:29:31,076 --> 00:29:32,940 over millions of years. 788 00:29:33,008 --> 00:29:34,639 >> Volcanoes form above 789 00:29:34,740 --> 00:29:36,471 subduction zones not because 790 00:29:36,539 --> 00:29:37,904 the Earth is hotter there but 791 00:29:38,005 --> 00:29:39,103 because this is where we're 792 00:29:39,204 --> 00:29:41,102 taking the water that once was 793 00:29:41,170 --> 00:29:42,901 in the ocean. It gets taken 794 00:29:42,969 --> 00:29:44,634 into the mantle and gets 795 00:29:44,701 --> 00:29:46,433 sweated out, causes the mantle 796 00:29:46,534 --> 00:29:47,898 to melt and this magma is what 797 00:29:47,966 --> 00:29:49,065 then rises and erupts 798 00:29:49,099 --> 00:29:50,497 explosively out these 799 00:29:50,531 --> 00:29:51,696 volcanoes. 800 00:29:58,061 --> 00:29:59,159 >> The water in the sediment 801 00:29:59,260 --> 00:30:01,324 forces magma to swirl up and 802 00:30:01,425 --> 00:30:04,223 push through the plate above. 803 00:30:04,291 --> 00:30:05,222 And when it breaks the 804 00:30:05,323 --> 00:30:07,554 surface, it creates volcanoes, 805 00:30:07,589 --> 00:30:09,153 like the volcanoes that form 806 00:30:09,221 --> 00:30:11,319 the Mariana Islands. 807 00:30:13,385 --> 00:30:14,916 It was subduction that formed 808 00:30:14,951 --> 00:30:18,581 the islands west of the trench 809 00:30:18,649 --> 00:30:20,114 and gave investigators the 810 00:30:20,215 --> 00:30:21,113 breakthrough they'd been 811 00:30:21,180 --> 00:30:24,845 looking for. Because here, at 812 00:30:24,911 --> 00:30:26,744 last, was a process powerful 813 00:30:26,810 --> 00:30:28,643 enough to create the Marianas 814 00:30:28,709 --> 00:30:32,474 Trench. As the descending 815 00:30:32,540 --> 00:30:34,805 plate dives down, it digs into 816 00:30:34,873 --> 00:30:37,004 the mantle. Here, the 817 00:30:37,071 --> 00:30:38,370 colliding plates form a 818 00:30:38,437 --> 00:30:40,602 trench, a giant crease in 819 00:30:40,637 --> 00:30:42,534 the ocean floor. 820 00:30:44,167 --> 00:30:45,699 It seemed that scientists had 821 00:30:45,800 --> 00:30:47,165 finally explained how the 822 00:30:47,232 --> 00:30:49,430 trench was formed. 823 00:30:50,697 --> 00:30:54,128 There was just one problem. A 824 00:30:54,162 --> 00:30:57,559 very large problem. Around the 825 00:30:57,593 --> 00:30:59,424 world, subduction zones cause 826 00:30:59,492 --> 00:31:00,757 violent earthquakes and 827 00:31:00,858 --> 00:31:03,123 catastrophic tsunamis. 828 00:31:05,322 --> 00:31:06,021 >> We know subduction is 829 00:31:06,122 --> 00:31:07,320 happening because of the 830 00:31:07,388 --> 00:31:08,386 active earthquakes and these 831 00:31:08,454 --> 00:31:10,019 are the most devastating 832 00:31:10,087 --> 00:31:13,750 earthquakes. This is the 833 00:31:13,818 --> 00:31:14,882 earthquake that generated e 834 00:31:14,984 --> 00:31:19,347 tsunami in Sumatra, also the 835 00:31:19,448 --> 00:31:20,512 other very large earthquakes 836 00:31:20,580 --> 00:31:21,613 in Alaska and Chile. 837 00:31:25,477 --> 00:31:27,142 >> But the Marianas Trench, 838 00:31:27,244 --> 00:31:28,841 the deepest subduction zone in 839 00:31:28,875 --> 00:31:30,507 the world, hasn't caused a 840 00:31:30,574 --> 00:31:32,039 devastating earthquake since 841 00:31:32,107 --> 00:31:33,672 records began in the 17th 842 00:31:33,772 --> 00:31:37,036 century. Investigators needed 843 00:31:37,137 --> 00:31:38,302 to know why. 844 00:31:38,403 --> 00:31:40,201 >> Ah, that's--that's, uh, the 845 00:31:40,302 --> 00:31:41,834 $60,000 question. 846 00:31:45,499 --> 00:31:46,564 >> They hoped the trench's 847 00:31:46,632 --> 00:31:48,197 shallower western edge might 848 00:31:48,265 --> 00:31:49,929 provide the answer. 849 00:31:57,060 --> 00:31:58,525 Here, they found an intriguing 850 00:31:58,593 --> 00:32:00,490 chain of underwater hills two 851 00:32:00,525 --> 00:32:01,956 miles below the surface of the 852 00:32:02,023 --> 00:32:04,021 sea. 853 00:32:07,820 --> 00:32:09,551 Engineers drilled down into 854 00:32:09,652 --> 00:32:10,917 the hills and collected core 855 00:32:11,018 --> 00:32:12,250 samples. 856 00:32:17,615 --> 00:32:18,713 An$ when the scientists 857 00:32:18,781 --> 00:32:20,445 analyzed the samples, they 858 00:32:20,546 --> 00:32:21,445 discovered the hills were 859 00:32:21,513 --> 00:32:24,510 actually volcanoes, and they 860 00:32:24,544 --> 00:32:29,141 spewed out not lava, but mud. 861 00:32:30,607 --> 00:32:32,505 The fine, powdery mud is made 862 00:32:32,606 --> 00:32:34,504 up of a soft type of rock that 863 00:32:34,605 --> 00:32:35,736 has been ground up in the 864 00:32:35,837 --> 00:32:39,368 subduction zone. It seemed 865 00:32:39,436 --> 00:32:41,067 this soft rock might explain 866 00:32:41,101 --> 00:32:42,300 why there have been no 867 00:32:42,367 --> 00:32:43,632 major earthquakes at the 868 00:32:43,733 --> 00:32:45,731 Marianas Trench. 869 00:32:46,798 --> 00:32:47,829 >> Everybody has a sense of 870 00:32:47,897 --> 00:32:49,995 what a volcano is but not all 871 00:32:50,096 --> 00:32:51,727 volcanoes erupt igneous rocks, 872 00:32:51,795 --> 00:32:54,226 there's some volcanoes that 873 00:32:54,260 --> 00:32:56,592 erupt mud. And a certain kind 874 00:32:56,626 --> 00:32:58,157 of unusual kind of mud in the 875 00:32:58,258 --> 00:32:59,956 Marianas is made out of 876 00:32:59,990 --> 00:33:01,689 serpentine, and serpentine is 877 00:33:01,789 --> 00:33:04,254 a very weak rock and it can be 878 00:33:04,321 --> 00:33:05,786 scratched with a knife or 879 00:33:05,854 --> 00:33:07,885 something like that. 880 00:33:09,052 --> 00:33:10,651 >> Investigators realized the 881 00:33:10,685 --> 00:33:12,483 grinding plates crush the soft 882 00:33:12,551 --> 00:33:14,714 rock to form a lubricating mud 883 00:33:14,749 --> 00:33:15,980 that prevents large 884 00:33:16,015 --> 00:33:19,745 earthquakes. Then the mud 885 00:33:19,812 --> 00:33:21,511 bubbles up to the ocean floor, 886 00:33:21,545 --> 00:33:23,177 where it forms the strange mud 887 00:33:23,278 --> 00:33:24,875 volcanoes found along the 888 00:33:24,910 --> 00:33:27,440 trench's western edge. 889 00:33:27,542 --> 00:33:28,806 >> Other parts of the world, 890 00:33:28,874 --> 00:33:29,972 like the Andes or maybe 891 00:33:30,040 --> 00:33:31,605 Indonesia, you've got two 892 00:33:31,706 --> 00:33:32,604 plates that are grinding 893 00:33:32,672 --> 00:33:34,037 together and the--one 894 00:33:34,071 --> 00:33:35,702 of the plates is quite strong, 895 00:33:35,770 --> 00:33:37,235 and it takes a big earthquake 896 00:33:37,336 --> 00:33:38,501 to rupture that plate 897 00:33:38,569 --> 00:33:40,433 interface. But if these rocks 898 00:33:40,501 --> 00:33:41,799 are weak like they are in the 899 00:33:41,867 --> 00:33:42,932 Marianas, where you've got 900 00:33:42,966 --> 00:33:44,498 these serpentinites, those 901 00:33:44,565 --> 00:33:45,697 are very weak and it doesn't 902 00:33:45,765 --> 00:33:47,530 take much energy at all to get 903 00:33:47,597 --> 00:33:48,862 the two plates to glide one 904 00:33:48,930 --> 00:33:50,327 past the other. 905 00:33:53,194 --> 00:33:55,025 >> At last, geologists had 906 00:33:55,093 --> 00:33:56,558 discovered what created the 907 00:33:56,592 --> 00:33:58,723 Marianas Trench. 908 00:34:00,123 --> 00:34:01,754 50 million years ago, the 909 00:34:01,822 --> 00:34:03,020 Pacific Plate slipped under 910 00:34:03,088 --> 00:34:04,187 the edge of the Philippine 911 00:34:04,287 --> 00:34:07,085 Plate. As it bent and dived 912 00:34:07,119 --> 00:34:08,618 into the Earth's mantle, it 913 00:34:08,652 --> 00:34:10,450 formed the colossal Marianas 914 00:34:10,518 --> 00:34:14,348 Trench. And the plate is still 915 00:34:14,415 --> 00:34:16,980 moving. Like a giant conveyor 916 00:34:17,080 --> 00:34:18,445 belt, the Earth's crust 917 00:34:18,513 --> 00:34:20,178 travels slowly across the 918 00:34:20,245 --> 00:34:21,776 Pacific Plate, from its 919 00:34:21,811 --> 00:34:22,976 birthplace in the East 920 00:34:23,043 --> 00:34:24,342 Pacific Ridge to its 921 00:34:24,409 --> 00:34:26,607 graveyard, 10,000 miles away 922 00:34:26,708 --> 00:34:28,772 in the Marianas Trench. 923 00:34:30,606 --> 00:34:32,071 Today, the Pacific Plate's 924 00:34:32,139 --> 00:34:33,504 movement can be tracked in 925 00:34:33,605 --> 00:34:35,035 real time. 926 00:34:36,569 --> 00:34:38,034 >> Confirmation has come from 927 00:34:38,135 --> 00:34:39,766 GPS technology, where we can 928 00:34:39,834 --> 00:34:42,499 actually put a transmitter on 929 00:34:42,565 --> 00:34:43,930 an island and come back year 930 00:34:44,031 --> 00:34:45,663 after year and actually follow 931 00:34:45,731 --> 00:34:47,562 it moving a few centimeters a 932 00:34:47,630 --> 00:34:49,294 year towards the trench. 933 00:34:51,560 --> 00:34:53,025 >> It's devouring the crust at 934 00:34:53,127 --> 00:34:55,457 a rate of three inches a year, 935 00:34:55,558 --> 00:34:56,990 about as fast as a human 936 00:34:57,024 --> 00:34:59,089 fingernail grows. 937 00:35:01,088 --> 00:35:03,086 Every four million years, it 938 00:35:03,154 --> 00:35:04,652 swallows an area the size of 939 00:35:04,720 --> 00:35:07,284 the United States. By 940 00:35:07,352 --> 00:35:08,816 consuming the crust created at 941 00:35:08,884 --> 00:35:10,349 the Pacific Ocean Ridge, 942 00:35:10,450 --> 00:35:12,148 the ravenous Marianas Trench 943 00:35:12,182 --> 00:35:13,547 is the world's largest 944 00:35:13,615 --> 00:35:15,246 recycling plant. 945 00:35:21,144 --> 00:35:22,875 But there was one remaining 946 00:35:22,976 --> 00:35:24,707 and major piece of the puzzle 947 00:35:24,775 --> 00:35:27,206 to find. Scientists still 948 00:35:27,240 --> 00:35:28,772 didn't know why it is the 949 00:35:28,873 --> 00:35:30,771 deepest trench on Earth. 950 00:35:32,804 --> 00:35:34,203 They suspected the age of the 951 00:35:34,236 --> 00:35:35,501 sea floor at the bottom of the 952 00:35:35,569 --> 00:35:38,300 trench may provide the answer. 953 00:35:38,367 --> 00:35:39,133 >> It turns out there's a 954 00:35:39,201 --> 00:35:40,566 really strong relationship 955 00:35:40,632 --> 00:35:42,198 between the age of the sea 956 00:35:42,265 --> 00:35:43,764 floor and its depth in the 957 00:35:43,831 --> 00:35:45,030 water. 958 00:35:47,929 --> 00:35:50,259 >> In 1999, a team of deep sea 959 00:35:50,294 --> 00:35:51,725 drillers returned to the 960 00:35:51,827 --> 00:35:52,791 trench to collect core 961 00:35:52,826 --> 00:35:54,624 samples. 962 00:35:55,924 --> 00:35:56,889 >> PLANK: One great thing 963 00:35:56,924 --> 00:35:57,888 about drilling this ocean 964 00:35:57,923 --> 00:35:58,922 crust is we actually got 965 00:35:58,989 --> 00:36:01,454 pieces of it. So, we're 966 00:36:01,555 --> 00:36:03,186 holding in our hands here the 967 00:36:03,253 --> 00:36:04,218 material that's actually getting 968 00:36:04,252 --> 00:36:05,351 subducted at the Marianas 969 00:36:05,453 --> 00:36:06,817 Trench, and it turned out to 970 00:36:06,884 --> 00:36:09,682 be 170 million years old. So 971 00:36:09,716 --> 00:36:10,714 we can say with confidence 972 00:36:10,782 --> 00:36:12,347 that's the oldest ocean floor 973 00:36:12,415 --> 00:36:13,580 before it's getting swallowed 974 00:36:13,614 --> 00:36:14,979 up in the mantle at the 975 00:36:15,046 --> 00:36:16,611 trench. 976 00:36:16,679 --> 00:36:18,577 >> But why is this piece of 977 00:36:18,611 --> 00:36:20,576 rock the oldest on the ocean 978 00:36:20,610 --> 00:36:22,408 floor? 979 00:36:22,509 --> 00:36:23,474 >> PLANK: The sea floor at the 980 00:36:23,508 --> 00:36:25,140 Marianas Trench is so old 981 00:36:25,208 --> 00:36:26,939 because it's been so long 982 00:36:27,040 --> 00:36:28,571 since it was born, so it was 983 00:36:28,639 --> 00:36:30,004 born in the equivalent of the 984 00:36:30,038 --> 00:36:31,503 eastern Pacific today and it's 985 00:36:31,571 --> 00:36:33,668 just been going on longer 986 00:36:33,769 --> 00:36:35,101 than--than any other place in 987 00:36:35,202 --> 00:36:36,300 the oceans before it's been 988 00:36:36,368 --> 00:36:37,766 subducted. 989 00:36:40,099 --> 00:36:41,264 >> The Pacific Plate is the 990 00:36:41,298 --> 00:36:42,663 planet's largest tectonic 991 00:36:42,731 --> 00:36:44,729 plate, covering an area 11 992 00:36:44,797 --> 00:36:46,428 times the size of the United 993 00:36:46,462 --> 00:36:48,094 States. 994 00:36:51,893 --> 00:36:53,323 When crust bubbled up at the 995 00:36:53,358 --> 00:36:55,889 ridge 170 million years ago, 996 00:36:55,956 --> 00:36:58,721 it was light and buoyant. 997 00:36:58,789 --> 00:37:00,353 But as it traveled 10,000 998 00:37:00,421 --> 00:37:02,419 miles across the plate, it 999 00:37:02,520 --> 00:37:04,251 cooled and became compact and 1000 00:37:04,352 --> 00:37:07,616 dense. Over millions of years, 1001 00:37:07,683 --> 00:37:09,314 the dense crust got heavier 1002 00:37:09,349 --> 00:37:10,680 and began to sink into the 1003 00:37:10,748 --> 00:37:12,313 mantle below. 1004 00:37:17,145 --> 00:37:18,576 Scientists realized that, 1005 00:37:18,644 --> 00:37:19,675 because the crust at the 1006 00:37:19,743 --> 00:37:21,374 Marianas Trench is the oldest 1007 00:37:21,409 --> 00:37:23,407 ocean crust, it's also the 1008 00:37:23,474 --> 00:37:25,106 heaviest and so has sunk 1009 00:37:25,206 --> 00:37:26,638 deeper into the mantle than 1010 00:37:26,672 --> 00:37:29,669 any other area of ocean crust. 1011 00:37:32,569 --> 00:37:34,101 Here, at last, was the 1012 00:37:34,201 --> 00:37:35,633 explanation for the trench's 1013 00:37:35,734 --> 00:37:39,098 extraordinary depth. The 1014 00:37:39,166 --> 00:37:40,530 picture of the Marianas Trench 1015 00:37:40,564 --> 00:37:42,729 is almost complete. 1016 00:37:44,462 --> 00:37:46,993 Volcanic islands mirroring the 1017 00:37:47,094 --> 00:37:47,993 trench's exact shape lead 1018 00:37:48,094 --> 00:37:49,625 scientists to believe it runs 1019 00:37:49,726 --> 00:37:52,257 along a subduction zone. 1020 00:37:52,358 --> 00:37:54,156 And slippery mud volcanoes 1021 00:37:54,224 --> 00:37:55,988 explain why it doesn't create 1022 00:37:56,056 --> 00:37:58,854 large earthquakes. But one 1023 00:37:58,888 --> 00:38:01,585 question remains unanswered. 1024 00:38:01,619 --> 00:38:02,785 Towards the trench's southern 1025 00:38:02,852 --> 00:38:06,116 end, the vast chasm drops a 1026 00:38:06,150 --> 00:38:07,849 further two miles to its 1027 00:38:07,883 --> 00:38:09,681 lowest point, the Challenger 1028 00:38:09,749 --> 00:38:11,846 Deep, seven miles beneath the 1029 00:38:11,947 --> 00:38:15,877 waves. The question is, what 1030 00:38:15,945 --> 00:38:19,575 makes it plunge so deep? 1031 00:38:24,284 --> 00:38:25,482 The investigation into the 1032 00:38:25,516 --> 00:38:27,481 Marianas Trench has one final 1033 00:38:27,548 --> 00:38:29,179 puzzle to solve. 1034 00:38:31,179 --> 00:38:32,711 At the trench's southern end, 1035 00:38:32,746 --> 00:38:34,077 the sea floor plummets a 1036 00:38:34,177 --> 00:38:37,142 further 10,000 feet into a 1037 00:38:37,176 --> 00:38:39,074 seven mile deep chasm called 1038 00:38:39,142 --> 00:38:42,339 the Challenger Deep. It's the 1039 00:38:42,439 --> 00:38:45,271 lowest point on the planet, 1040 00:38:45,338 --> 00:38:47,270 but so far, scientists have 1041 00:38:47,337 --> 00:38:49,601 been unable to explain why 1042 00:38:49,702 --> 00:38:51,800 this one section of the trench 1043 00:38:51,868 --> 00:38:55,864 is so deep. Now, they believe 1044 00:38:55,932 --> 00:38:57,197 the shape of the descending 1045 00:38:57,265 --> 00:38:59,296 tectonic plate may hold the 1046 00:38:59,364 --> 00:39:00,729 answer. 1047 00:39:00,830 --> 00:39:01,628 >> The Challenger Deep, in 1048 00:39:01,662 --> 00:39:03,094 addition, is a little bit 1049 00:39:03,161 --> 00:39:05,093 deeper, because of some 1050 00:39:05,160 --> 00:39:07,791 peculiarities relating to how 1051 00:39:07,826 --> 00:39:09,457 the slab that's going down is 1052 00:39:09,558 --> 00:39:11,056 behaving. 1053 00:39:12,357 --> 00:39:14,320 >> A narrow slab of crust has 1054 00:39:14,355 --> 00:39:15,820 torn away from the Pacific 1055 00:39:15,887 --> 00:39:18,151 Plate's descending edge. 1056 00:39:18,253 --> 00:39:19,185 >> STERN: Well, it's basically 1057 00:39:19,253 --> 00:39:20,683 got to do with how the slab 1058 00:39:20,718 --> 00:39:21,783 pushes the mantle out of the 1059 00:39:21,884 --> 00:39:24,082 way. Where you have a narrow 1060 00:39:24,149 --> 00:39:25,615 slab, like you have at the 1061 00:39:25,716 --> 00:39:27,614 Challenger Deep, it can sink 1062 00:39:27,680 --> 00:39:29,412 almost vertically, because the 1063 00:39:29,513 --> 00:39:30,678 mantle that it's trying to 1064 00:39:30,746 --> 00:39:32,244 displace can move around out 1065 00:39:32,311 --> 00:39:33,776 of the way. 1066 00:39:36,042 --> 00:39:37,641 Investigators have finally 1067 00:39:37,675 --> 00:39:39,206 unraveled the mysteries of the 1068 00:39:39,274 --> 00:39:41,205 Marianas Trench. 1069 00:39:43,505 --> 00:39:45,203 And in the process, they've 1070 00:39:45,304 --> 00:39:46,402 made a discovery with 1071 00:39:46,470 --> 00:39:48,368 implications that stretch far 1072 00:39:48,436 --> 00:39:50,967 beyond the trench itself. 1073 00:39:56,564 --> 00:39:58,495 Studying the ocean ridges led 1074 00:39:58,530 --> 00:40:00,162 geologists to believe that 1075 00:40:00,229 --> 00:40:01,627 magma, welling up at the 1076 00:40:01,728 --> 00:40:03,392 ridges, was pushing the plates 1077 00:40:03,460 --> 00:40:06,024 apart. 1078 00:40:06,092 --> 00:40:08,556 >> How much weight is that-- 1079 00:40:08,624 --> 00:40:09,989 >> But the exploration of the 1080 00:40:10,023 --> 00:40:11,888 Marianas Trench has changed 1081 00:40:11,922 --> 00:40:14,286 this idea forever. 1082 00:40:14,354 --> 00:40:16,053 >> People used to think that 1083 00:40:16,087 --> 00:40:17,818 maybe the magma would kind of 1084 00:40:17,886 --> 00:40:20,183 push the plates apart, and 1085 00:40:20,251 --> 00:40:22,548 that idea is largely 1086 00:40:22,616 --> 00:40:24,547 discounted now. 1087 00:40:25,981 --> 00:40:27,446 >> As the ocean crust travels 1088 00:40:27,514 --> 00:40:28,879 from the Pacific Ocean Ridge 1089 00:40:28,946 --> 00:40:31,244 to the trench, it changes from 1090 00:40:31,345 --> 00:40:33,409 a buoyant, red-hot magma into 1091 00:40:33,476 --> 00:40:35,575 a colder, denser and heavier 1092 00:40:35,609 --> 00:40:39,506 crust. The plate's leading 1093 00:40:39,574 --> 00:40:41,671 edge becomes so heavy that it 1094 00:40:41,772 --> 00:40:43,170 drags the rest of the plate 1095 00:40:43,238 --> 00:40:45,136 along behind it. 1096 00:40:46,369 --> 00:40:48,767 >> The heavy cold plates at 1097 00:40:48,834 --> 00:40:51,200 the trenches are sinking down 1098 00:40:51,300 --> 00:40:53,931 into the mantle and pulling 1099 00:40:54,032 --> 00:40:56,297 the plates apart, uh, at the 1100 00:40:56,363 --> 00:40:58,528 ridges, and the magma just 1101 00:40:58,563 --> 00:41:00,460 passively, uh, fills in the 1102 00:41:00,528 --> 00:41:01,927 gaps. 1103 00:41:04,926 --> 00:41:06,291 >> The investigation into the 1104 00:41:06,358 --> 00:41:07,523 Marianas Trench has 1105 00:41:07,558 --> 00:41:08,722 revolutionized our 1106 00:41:08,823 --> 00:41:09,988 understanding of how the 1107 00:41:10,056 --> 00:41:11,987 Earth's plates move. 1108 00:41:15,153 --> 00:41:17,084 We now know a worldwide 1109 00:41:17,152 --> 00:41:19,217 network of subduction zones 1110 00:41:19,251 --> 00:41:21,149 drag tectonic plates around 1111 00:41:21,249 --> 00:41:23,780 the globe, powering the 1112 00:41:23,881 --> 00:41:25,246 movement of continents over 1113 00:41:25,314 --> 00:41:28,511 millions of years and moving 1114 00:41:28,579 --> 00:41:31,509 the very Earth we stand on. 1115 00:41:32,943 --> 00:41:34,241 >> The plates that are moving 1116 00:41:34,309 --> 00:41:36,040 fastest on the Earth are 1117 00:41:36,108 --> 00:41:37,740 the ones that have all the 1118 00:41:37,774 --> 00:41:39,105 trenches. 1119 00:41:40,306 --> 00:41:41,404 >> The Pacific Plate is the 1120 00:41:41,472 --> 00:41:42,936 fastest moving of the nine 1121 00:41:43,037 --> 00:41:44,902 major plates on the planet, 1122 00:41:44,936 --> 00:41:46,401 because it is surrounded by 1123 00:41:46,469 --> 00:41:48,367 dozens of destructive trenches 1124 00:41:48,401 --> 00:41:51,365 like the Marianas. They are 1125 00:41:51,432 --> 00:41:53,197 consuming the ocean crust 1126 00:41:53,298 --> 00:41:54,830 faster than the Ocean Ridge 1127 00:41:54,931 --> 00:41:57,995 can produce it. Over millions 1128 00:41:58,062 --> 00:41:59,727 of years, the Pacific Plate 1129 00:41:59,828 --> 00:42:02,359 will shrink until, some time 1130 00:42:02,426 --> 00:42:04,324 in the distant future, the 1131 00:42:04,359 --> 00:42:06,623 largest ocean on Earth will 1132 00:42:06,690 --> 00:42:08,955 disappear. Australia will 1133 00:42:08,990 --> 00:42:10,787 crash into the United States, 1134 00:42:10,855 --> 00:42:13,052 reshaping our planet. 1135 00:42:14,520 --> 00:42:16,417 Perhaps one day, downtown 1136 00:42:16,519 --> 00:42:17,983 Seattle will compete for real 1137 00:42:18,050 --> 00:42:19,150 estate with a suburb of 1138 00:42:19,250 --> 00:42:22,114 Sydney, Australia. And 1139 00:42:22,149 --> 00:42:23,580 all because of subduction 1140 00:42:23,615 --> 00:42:25,045 zones like the Marianas 1141 00:42:25,113 --> 00:42:26,045 Trench. 1142 00:42:31,210 --> 00:42:33,208 But for all its significance, 1143 00:42:33,276 --> 00:42:35,107 man has only ever dived to the 1144 00:42:35,207 --> 00:42:37,572 bottom of the trench once, and 1145 00:42:37,673 --> 00:42:39,005 there are no immediate plans 1146 00:42:39,038 --> 00:42:40,936 to return. 1147 00:42:41,004 --> 00:42:45,901 >> Imagine asking someone, 1148 00:42:45,935 --> 00:42:49,898 "What is the flora and fauna 1149 00:42:49,999 --> 00:42:52,630 of California?" and saying 1150 00:42:52,731 --> 00:42:54,462 that someone's spent ten 1151 00:42:54,530 --> 00:42:56,961 minutes there, picked up two 1152 00:42:56,995 --> 00:42:59,093 ants, come back and said 1153 00:42:59,161 --> 00:43:01,092 they've sampled California. 1154 00:43:01,160 --> 00:43:02,525 That's probably how well we 1155 00:43:02,593 --> 00:43:03,891 know the Marianas Trench. 1156 00:43:08,256 --> 00:43:09,987 >> To date, less than five per 1157 00:43:10,055 --> 00:43:11,420 cent of the world's oceans 1158 00:43:11,521 --> 00:43:14,151 have been explored. But only 1159 00:43:14,219 --> 00:43:15,584 by returning to the oceans' 1160 00:43:15,685 --> 00:43:17,683 very deepest reaches will we 1161 00:43:17,750 --> 00:43:19,215 fully comprehend the 1162 00:43:19,282 --> 00:43:21,380 incredible forces that recycle 1163 00:43:21,415 --> 00:43:24,113 and rebuild our world. 1164 00:43:25,779 --> 00:43:27,577 >> The way I like to think of 1165 00:43:27,644 --> 00:43:31,441 it is that ocean exploration 1166 00:43:31,476 --> 00:43:32,941 leads to new research 1167 00:43:33,008 --> 00:43:36,839 questions. And if we don't 1168 00:43:36,940 --> 00:43:39,204 have exploration, we don't 1169 00:43:39,271 --> 00:43:40,837 even know the right questions 1170 00:43:40,903 --> 00:43:42,368 to ask. 1171 00:43:44,268 --> 00:43:45,733 It is now known what a 1172 00:43:45,801 --> 00:43:47,799 geological wonder the Marianas 1173 00:43:47,900 --> 00:43:52,163 Trench is. Since this deep 1174 00:43:52,264 --> 00:43:53,962 chasm in the Earth's crust was 1175 00:43:53,996 --> 00:43:55,428 first discovered with a length 1176 00:43:55,496 --> 00:43:57,160 of rope and a lump of lead 1177 00:43:57,261 --> 00:43:58,759 more than a century ago, 1178 00:43:58,793 --> 00:44:01,591 evidence has piled up. A 1179 00:44:01,692 --> 00:44:03,423 record-breaking dive to the 1180 00:44:03,491 --> 00:44:06,322 lowest point on Earth. Giant 1181 00:44:06,422 --> 00:44:08,154 undersea mountain ranges with 1182 00:44:08,222 --> 00:44:09,753 bizarre magnetic zebra 1183 00:44:09,787 --> 00:44:11,952 stripes, proof that the ocean 1184 00:44:12,020 --> 00:44:13,784 crust is spreading towards 1185 00:44:13,852 --> 00:44:16,116 the hungry Marianas Trench, 1186 00:44:16,184 --> 00:44:17,649 lined with slippery mud 1187 00:44:17,683 --> 00:44:19,115 volcanoes which prevent 1188 00:44:19,182 --> 00:44:21,647 devastating earthquakes. 1189 00:44:21,681 --> 00:44:23,812 And the planet's oldest ocean 1190 00:44:23,846 --> 00:44:25,577 crust, the reason that the 1191 00:44:25,645 --> 00:44:27,576 Marianas Trench is the deepest 1192 00:44:27,644 --> 00:44:29,842 point in the oceans. 1193 00:44:30,909 --> 00:44:33,007 In the darkest and most remote 1194 00:44:33,041 --> 00:44:35,372 place in the world, scientists 1195 00:44:35,473 --> 00:44:36,905 have added to their knowledge 1196 00:44:36,972 --> 00:44:39,270 about the powerful forces that 1197 00:44:39,371 --> 00:44:41,069 contribute to the dynamic 1198 00:44:41,170 --> 00:44:42,701 story of our planet.