1 00:00:03,847 --> 00:00:10,007 Earth, a 4.5- Billion-year-old planet, still evolving. 2 00:00:10,007 --> 00:00:18,287 As continents shift and clash, volcanoes erupt, and glaciers grow and recede, 3 00:00:18,287 --> 00:00:22,527 the Earth's crust is carved in countless fascinating ways, 4 00:00:22,527 --> 00:00:26,236 leaving a trail of geological mysteries behind. 5 00:00:27,327 --> 00:00:31,647 This episode investigates one awesome force that shapes the Earth. 6 00:00:31,647 --> 00:00:38,883 It's extraterrestrial, and it doesn't happen over millions of years, but in seconds. 7 00:00:41,567 --> 00:00:46,047 It's a force caused by an immense impact from asteroids - 8 00:00:46,047 --> 00:00:48,515 giant rocks from space. 9 00:00:50,927 --> 00:00:55,007 The investigation of asteroid strikes has given scientists insight 10 00:00:55,007 --> 00:00:56,847 into the formation of the universe, 11 00:00:56,847 --> 00:01:01,398 providing a window into planet Earth's ancient past. 12 00:01:07,887 --> 00:01:14,167 There is a giant hole in the Arizona desert, 35 miles east of Flagstaff. 13 00:01:14,167 --> 00:01:20,487 It's huge, three quarters of a mile wide and 550 feet deep. 14 00:01:20,487 --> 00:01:23,687 The Washington monument could fit inside it. 15 00:01:23,687 --> 00:01:28,007 The mystery confronting geologists in the late 19th century was, 16 00:01:28,007 --> 00:01:30,047 how did this happen? 17 00:01:30,047 --> 00:01:35,485 People agreed that only a massive force could have created such a huge chasm. 18 00:01:36,647 --> 00:01:38,763 But what was this force? 19 00:01:40,207 --> 00:01:43,567 The most likely theory was that a huge volcanic explosion 20 00:01:43,567 --> 00:01:46,167 had ruptured the rugged landscape. 21 00:01:46,167 --> 00:01:51,719 Scientists had discovered similar sized craters in volcanic areas before. 22 00:01:53,127 --> 00:01:58,567 But Grove Gilbert, chief geologist for the US Geological Survey, had another idea, 23 00:01:58,567 --> 00:02:02,447 one that came to him after observing craters on the moon 24 00:02:02,447 --> 00:02:05,407 through his telescope. 25 00:02:05,407 --> 00:02:08,087 He saw similarities between the moon's craters 26 00:02:08,087 --> 00:02:10,727 and the mysterious hole in the Arizona desert, 27 00:02:10,727 --> 00:02:15,367 leading him to speculate that the Arizona crater might have been caused 28 00:02:15,367 --> 00:02:18,487 by an asteroid impact. 29 00:02:18,487 --> 00:02:21,127 But this was just a theory. 30 00:02:21,127 --> 00:02:24,447 At the time, no-one had proven that any crater on Earth 31 00:02:24,447 --> 00:02:26,756 had been caused by an asteroid. 32 00:02:27,887 --> 00:02:32,915 So, in 1892, Gilbert decided to travel to the mysterious Arizona crater. 33 00:02:34,167 --> 00:02:37,727 He wondered if this could have an impact origin, 34 00:02:37,727 --> 00:02:40,287 or alternatively, a volcanic origin. 35 00:02:40,287 --> 00:02:44,121 And so he had these two competing hypotheses that he wanted to test. 36 00:02:46,047 --> 00:02:49,327 Gilbert assumed that if the crater was caused by an asteroid, 37 00:02:49,327 --> 00:02:53,327 he should find a giant, alien rock in the middle of it. 38 00:02:53,327 --> 00:02:55,443 But there was none. 39 00:02:56,607 --> 00:03:01,447 But he did see what he thought were signs that a volcano might be the cause. 40 00:03:01,447 --> 00:03:05,447 KRING: When Gilbert arrived, he realised that this hole in the ground 41 00:03:05,447 --> 00:03:09,567 was associated with some volcanic peaks in the distance, 42 00:03:09,567 --> 00:03:12,167 you can see them in the background over the rim, 43 00:03:12,167 --> 00:03:13,927 or beyond the rim of the crater, 44 00:03:13,927 --> 00:03:17,887 and so, immediately, I think, he was prejudiced, if you will, 45 00:03:17,887 --> 00:03:21,596 towards a volcanic, as opposed to a meteoritic origin. 46 00:03:22,847 --> 00:03:27,527 Not far from the mysterious crater, Gilbert found another, similar, giant hole. 47 00:03:27,527 --> 00:03:33,007 He declared this one as an unusual volcanic crater, called a maar. 48 00:03:33,007 --> 00:03:34,647 He knew that four years before, 49 00:03:34,647 --> 00:03:38,607 in Japan, scientists had witnessed the formation of a maar 50 00:03:38,607 --> 00:03:42,007 after a huge underground explosion of steam. 51 00:03:42,007 --> 00:03:45,847 The resulting crater resembled the giant hole Gilbert came across 52 00:03:45,847 --> 00:03:48,287 in the Arizona desert. 53 00:03:48,287 --> 00:03:52,527 They are produced when basaltic magma rises through the Earth's crust, 54 00:03:52,527 --> 00:03:59,287 encounters groundwater, creating a steam explosion, which causes a blast 55 00:03:59,287 --> 00:04:02,518 that produces craters like the one, uh, over my shoulder. 56 00:04:03,927 --> 00:04:08,447 Intriguingly, the two almost identical craters were only 50 miles apart 57 00:04:08,447 --> 00:04:11,087 in the same desert. 58 00:04:11,087 --> 00:04:15,687 One was known to have been caused by an underground steam explosion. 59 00:04:15,687 --> 00:04:19,407 Because of their close proximity, Gilbert concluded 60 00:04:19,407 --> 00:04:23,007 that the mysterious crater was also caused by volcanic activity. 61 00:04:23,007 --> 00:04:27,727 In 1896, he published his findings in an influential report 62 00:04:27,727 --> 00:04:31,720 and, for the wider geological community, the debate was resolved. 63 00:04:34,487 --> 00:04:37,247 But, six years after Gilbert's findings, 64 00:04:37,247 --> 00:04:40,047 American entrepreneur and mining engineer Daniel Barringer 65 00:04:40,047 --> 00:04:43,127 arrived on the same scene. 66 00:04:43,127 --> 00:04:48,167 He was intrigued by mysterious small iron rocks shepherds had found 67 00:04:48,167 --> 00:04:51,607 around the crater while grazing their herds. 68 00:04:51,607 --> 00:04:56,407 Barringer was convinced that Gilbert was wrong about the crater's origins. 69 00:04:56,407 --> 00:05:00,927 I'm holding in my hands a fragment of what started it all. 70 00:05:00,927 --> 00:05:05,367 It is not the type of material that one finds in any other geological terrain 71 00:05:05,367 --> 00:05:08,607 or created by any terrestrial geologic process. 72 00:05:08,607 --> 00:05:12,247 Iron in rock is usually mixed with other minerals. 73 00:05:12,247 --> 00:05:16,967 But at the mysterious crater, the iron was almost pure. 74 00:05:16,967 --> 00:05:21,887 And there were large amounts, normally not found on the earth's surface, 75 00:05:21,887 --> 00:05:25,960 spread over a huge area surrounding the crater. 76 00:05:28,367 --> 00:05:31,687 Barringer believed the pieces found here were meteorites, 77 00:05:31,687 --> 00:05:35,362 small space rocks that form when big asteroids break apart. 78 00:05:37,327 --> 00:05:40,887 He had a hunch that this huge hole in the desert was formed 79 00:05:40,887 --> 00:05:44,287 by a giant asteroid made largely from iron. 80 00:05:44,287 --> 00:05:48,487 Barringer immediately saw the commercial opportunities. 81 00:05:48,487 --> 00:05:50,567 From the crater's size, 82 00:05:50,567 --> 00:05:54,082 he calculated that the asteroid must have weighed ten million tons. 83 00:05:55,727 --> 00:05:58,367 With iron then at $80 a ton, 84 00:05:58,367 --> 00:06:02,121 Barringer was convinced he could become a rich man from mining the iron. 85 00:06:04,007 --> 00:06:09,047 So in 1903, Barringer bought the crater site of over 1,200 acres 86 00:06:09,047 --> 00:06:11,367 and hired crews to begin digging. 87 00:06:11,367 --> 00:06:15,645 Convinced it was an impact site, he named it Meteor Crater. 88 00:06:17,607 --> 00:06:21,007 KRING: We're in one of the remnants of Barringer's mining camp. 89 00:06:21,007 --> 00:06:25,687 This is a place where his miners lived, ate, slept, 90 00:06:25,687 --> 00:06:29,407 while they looked for the buried meteoritic mass 91 00:06:29,407 --> 00:06:32,447 that they thought was beneath the floor of the crater. 92 00:06:32,447 --> 00:06:36,407 For years, Barringer and his men found only small fragments of iron. 93 00:06:36,407 --> 00:06:41,167 Undeterred by this, they kept digging deeper shafts into the earth. 94 00:06:41,167 --> 00:06:44,047 KRING: The largest of which, the main shaft, you can see 95 00:06:44,047 --> 00:06:47,647 is a white island of debris in the centre of the crater. 96 00:06:47,647 --> 00:06:52,367 In fact, one of those holes close to me here reached a depth 97 00:06:52,367 --> 00:06:56,607 of nearly 1,400 feet beneath the surface of the Earth. 98 00:06:56,607 --> 00:07:02,007 In all of these cases, or most of these cases, they found telltale hints 99 00:07:02,007 --> 00:07:07,527 of the impacting meteoritic body, but no giant mass. 100 00:07:07,527 --> 00:07:10,527 Barringer did stumble across some clues, however. 101 00:07:10,527 --> 00:07:16,407 Strange and unique rock formations such as fine, pulverised rocks 102 00:07:16,407 --> 00:07:17,965 spread around the crater. 103 00:07:20,967 --> 00:07:27,167 He noticed, quite rightly, that it is so fine, it is almost like talcum powder, 104 00:07:27,167 --> 00:07:32,407 the type of thing that immediately alerted him to something unusual, 105 00:07:32,407 --> 00:07:36,480 in the geologic processes that shaped the land here. 106 00:07:37,527 --> 00:07:40,767 To Barringer, the pulverised rock was a major clue 107 00:07:40,767 --> 00:07:45,007 that pointed to one thing, the violent impact of an asteroid. 108 00:07:45,007 --> 00:07:48,407 As a geologist, if I saw this rock I would say, "OK, this is not something 109 00:07:48,407 --> 00:07:52,527 "that I see around a volcanic crater, there's something going on here. 110 00:07:52,527 --> 00:07:54,518 "And... and I need to figure it out." 111 00:07:57,127 --> 00:07:59,687 Barringer also discovered other oddities. 112 00:07:59,687 --> 00:08:04,681 At the crater rim, he noted a bed of rocks that were chaotically overturned. 113 00:08:05,687 --> 00:08:09,847 Dramatic energy uplifted the rocks in the crater wall behind me. 114 00:08:09,847 --> 00:08:11,927 Originally they were absolutely horizontal 115 00:08:11,927 --> 00:08:14,007 and you can see that they are tilted upwards, 116 00:08:14,007 --> 00:08:15,847 and if you look very closely, 117 00:08:15,847 --> 00:08:20,716 at the very top of the rim, they are completely overturned. 118 00:08:22,527 --> 00:08:27,487 For 27 years, Daniel Barringer obsessively sunk mining shafts 119 00:08:27,487 --> 00:08:31,685 in search of his giant iron asteroid, with no success. 120 00:08:32,687 --> 00:08:35,607 Barringer died in 1929, 121 00:08:35,607 --> 00:08:39,327 having lost 600,000 of his own and investors' money - 122 00:08:39,327 --> 00:08:43,607 ten million in today's dollars. 123 00:08:43,607 --> 00:08:46,405 The privately owned crater has remained in his family to this day. 124 00:08:47,487 --> 00:08:50,807 But his theory about the asteroid impact at Meteor Crater 125 00:08:50,807 --> 00:08:52,447 spurred further investigation 126 00:08:52,447 --> 00:08:55,757 based on three clues he had uncovered. 127 00:08:57,007 --> 00:09:02,087 The first, the pieces of pure iron scattered across the crater. 128 00:09:02,087 --> 00:09:06,407 Next, rock that had been crushed into fine powder. 129 00:09:06,407 --> 00:09:11,242 And finally, strange rocks thrown up and flipped over at the crater's rim. 130 00:09:12,447 --> 00:09:16,447 Interestingly, even though Barringer hadn't convinced 131 00:09:16,447 --> 00:09:20,727 the geologic community about the impact origin of this crater, 132 00:09:20,727 --> 00:09:23,967 he had launched at least a small number of people 133 00:09:23,967 --> 00:09:27,487 into an investigation of impact processes. 134 00:09:27,487 --> 00:09:30,007 Proof of Barringer's asteroid theory would get a boost, 135 00:09:30,007 --> 00:09:33,966 some six decades later, from an unexpected source. 136 00:09:43,007 --> 00:09:46,767 Meteor Crater in the Arizona desert was still a mystery 137 00:09:46,767 --> 00:09:48,485 to the geological community. 138 00:09:50,327 --> 00:09:55,367 The debate on whether it was caused by volcanic activity or an asteroid impact 139 00:09:55,367 --> 00:09:58,647 wasn't resolved until 1960. 140 00:09:58,647 --> 00:10:01,407 A young geologist, Eugene Shoemaker, 141 00:10:01,407 --> 00:10:04,167 became interested in Barringer's research. 142 00:10:04,167 --> 00:10:07,047 He would take the investigation in a new direction, 143 00:10:07,047 --> 00:10:08,807 which turned Meteor Crater 144 00:10:08,807 --> 00:10:12,767 into one of the most investigated crater sites on Earth. 145 00:10:12,767 --> 00:10:17,247 Shoemaker was working on craters left by nuclear explosions 146 00:10:17,247 --> 00:10:19,044 on test sites in Nevada. 147 00:10:20,047 --> 00:10:25,201 His task was to find out how the explosions transformed the landscape. 148 00:10:28,487 --> 00:10:32,567 Intriguingly, at the test sites, he found the exact same rock formations 149 00:10:32,567 --> 00:10:36,879 Barringer had described at the mysterious Meteor Crater in Arizona. 150 00:10:37,887 --> 00:10:40,687 Shoemaker passed away in 1997, 151 00:10:40,687 --> 00:10:45,363 but his wife, astronomer Carolyn Shoemaker, recalls his findings. 152 00:10:46,527 --> 00:10:48,567 Gene compared Meteor Crater 153 00:10:48,567 --> 00:10:52,967 with the craters that he had been mapping at the Nevada test site. 154 00:10:52,967 --> 00:10:57,487 At the test site, Gene saw overturned beds also, 155 00:10:57,487 --> 00:11:01,127 near the top of the craters in the rims. 156 00:11:01,127 --> 00:11:05,967 And that... that certainly told him that there was a strong similarity, 157 00:11:05,967 --> 00:11:09,247 because they were so obvious at Meteor Crater. 158 00:11:09,247 --> 00:11:11,847 Shoemaker came upon another important clue 159 00:11:11,847 --> 00:11:15,647 that linked the Nevada test sites to Meteor Crater. 160 00:11:15,647 --> 00:11:18,407 He found this samples of this very unusual rock. 161 00:11:18,407 --> 00:11:23,367 This was once sandstone, but he recognised it had been altered. 162 00:11:23,367 --> 00:11:27,087 In the craters left by explosions from nuclear bomb testing, 163 00:11:27,087 --> 00:11:30,047 Shoemaker discovered crystalline structures - 164 00:11:30,047 --> 00:11:33,596 the same structures found at Arizona's Meteor Crater. 165 00:11:36,607 --> 00:11:41,007 Today we understand that this is shocked sandstone glass, 166 00:11:41,007 --> 00:11:45,927 that is, the original sandstone, all of the quartz crystals were melted 167 00:11:45,927 --> 00:11:51,327 and put into a frothy, bubbly, glassy matrix which we have here. 168 00:11:51,327 --> 00:11:52,887 They were caused 169 00:11:52,887 --> 00:11:58,166 by the incredible energy released in the shockwaves of a nuclear blast. 170 00:12:04,927 --> 00:12:09,487 For Shoemaker, it was conclusive proof that the vast Meteor Crater 171 00:12:09,487 --> 00:12:11,687 wasn't formed by volcanic eruptions. 172 00:12:11,687 --> 00:12:17,956 Instead, it was created by a powerful asteroid impact in just a split second. 173 00:12:21,887 --> 00:12:27,405 The shocked rock also gave scientists a clue about the age of the crater. 174 00:12:30,487 --> 00:12:32,687 When an asteroid hits the Earth, 175 00:12:32,687 --> 00:12:36,607 the energy from the blast is absorbed by the surrounding rock. 176 00:12:36,607 --> 00:12:40,927 Using a process called thermoluminescence dating, 177 00:12:40,927 --> 00:12:43,967 scientists are able to measure the amount of energy 178 00:12:43,967 --> 00:12:46,959 the rock is giving off in the form of light. 179 00:12:49,887 --> 00:12:52,567 The shocked rock from Meteor Crater told them 180 00:12:52,567 --> 00:12:56,162 that the impact happened 50,000 years ago. 181 00:12:58,967 --> 00:13:03,047 But for some, there remained one problem with this theory. 182 00:13:03,047 --> 00:13:06,847 If the Arizona earth was crushed by a huge asteroid, 183 00:13:06,847 --> 00:13:09,839 where was the rock that made the impact? 184 00:13:10,967 --> 00:13:14,287 Scientists had a hunch that when it struck, 185 00:13:14,287 --> 00:13:16,367 the iron meteorite had vapourised. 186 00:13:16,367 --> 00:13:20,887 Conclusive evidence came in 1997 when scientists were able to simulate 187 00:13:20,887 --> 00:13:23,847 the impact using advanced computer modelling. 188 00:13:23,847 --> 00:13:25,647 From the size of the crater, 189 00:13:25,647 --> 00:13:29,527 they calculated that the asteroid must have weighed at least 300,000 tons 190 00:13:29,527 --> 00:13:31,085 when it struck. 191 00:13:33,327 --> 00:13:35,887 The data further revealed that it hit Earth 192 00:13:35,887 --> 00:13:39,687 at a speed of over 25,000 miles per hour. 193 00:13:39,687 --> 00:13:43,441 That's 35 times the speed of sound. 194 00:13:45,047 --> 00:13:48,767 Upon impact, the asteroid triggered a massive shockwave 195 00:13:48,767 --> 00:13:52,327 many times more powerful than a nuclear explosion. 196 00:13:52,327 --> 00:13:57,927 Within a matter of seconds, this impact crater behind me was excavated, 197 00:13:57,927 --> 00:14:01,767 and this debris was, uh, deposited on the landscape. 198 00:14:01,767 --> 00:14:04,007 Within seconds, the shockwave 199 00:14:04,007 --> 00:14:08,767 and the very high velocity air blast radiated across the landscape. 200 00:14:08,767 --> 00:14:13,487 The shockwave travelled back up through the asteroid's iron core, 201 00:14:13,487 --> 00:14:18,487 vapourising most of it, and scattering the rest in small pieces over a wide area, 202 00:14:18,487 --> 00:14:20,807 up to six miles away. 203 00:14:20,807 --> 00:14:24,407 The energy that produced this crater ranges somewhere 204 00:14:24,407 --> 00:14:28,047 from a few hundred to perhaps a thousand times greater 205 00:14:28,047 --> 00:14:30,847 than the energy that destroyed the cities of Hiroshima and Nagasaki 206 00:14:30,847 --> 00:14:32,405 in World War II. 207 00:14:33,687 --> 00:14:38,007 The investigation has uncovered reasons why there are no big remnants 208 00:14:38,007 --> 00:14:40,362 of asteroid rock in the Arizona crater. 209 00:14:41,767 --> 00:14:44,487 Crystalline structures in the rock showed evidence 210 00:14:44,487 --> 00:14:47,365 of a strong shockwave that followed the impact. 211 00:14:49,207 --> 00:14:53,327 Computer modelling revealed that the speed and size of the asteroid 212 00:14:53,327 --> 00:14:57,447 created enough energy for the rock to vapourise when it hit. 213 00:14:57,447 --> 00:15:01,367 This crater is particularly important because it is the youngest 214 00:15:01,367 --> 00:15:05,287 and most pristine impact crater on the surface of the Earth. 215 00:15:05,287 --> 00:15:09,687 It was also the first recognised impact crater on the surface of the Earth, 216 00:15:09,687 --> 00:15:12,487 and so it is in some sense the Rosetta site. 217 00:15:12,487 --> 00:15:14,527 It is the touchstone for geology. 218 00:15:14,527 --> 00:15:19,207 It is here that specialists from around the world come to study and learn 219 00:15:19,207 --> 00:15:23,207 about impact cratering as a geologic process. 220 00:15:23,207 --> 00:15:27,607 Since 1960, when Shoemaker proved that Meteor Crater was an impact site, 221 00:15:27,607 --> 00:15:30,047 geologists went looking for more. 222 00:15:30,047 --> 00:15:32,007 Armed with this new information 223 00:15:32,007 --> 00:15:34,847 and the developments in space and satellite technology, 224 00:15:34,847 --> 00:15:36,927 they would revolutionise our understanding 225 00:15:36,927 --> 00:15:40,966 of how asteroids have shaped the surface of the Earth. 226 00:15:46,687 --> 00:15:48,567 Once the Meteor Crater in Arizona 227 00:15:48,567 --> 00:15:53,047 proved an iron mass can burst from space and create a monster chasm, 228 00:15:53,047 --> 00:15:55,322 scientists began to search for others. 229 00:15:57,287 --> 00:16:00,487 They questioned whether some craters they thought of as volcanic 230 00:16:00,487 --> 00:16:03,479 were in fact caused by asteroids. 231 00:16:05,447 --> 00:16:09,087 The investigation turned to Sudbury in Ontario, Canada. 232 00:16:09,087 --> 00:16:13,167 There is no obvious crater but, for over 150 years, 233 00:16:13,167 --> 00:16:18,527 the city has been the centre of fabulous mining wealth and a geological mystery. 234 00:16:18,527 --> 00:16:22,687 3,000 feet below ground in one of Sudbury's mines, 235 00:16:22,687 --> 00:16:26,727 thick veins of copper and nickel are on view. 236 00:16:26,727 --> 00:16:32,287 Until recently, these mining riches were associated with volcanic activity. 237 00:16:32,287 --> 00:16:35,247 One of the really distinctive features of Sudbury is the fact 238 00:16:35,247 --> 00:16:39,127 that it has world class metal deposits associated with it. 239 00:16:39,127 --> 00:16:43,607 And originally, these were thought to be related to volcano activity, 240 00:16:43,607 --> 00:16:46,207 volcanic activity and magmas coming from inside the Earth, 241 00:16:46,207 --> 00:16:50,007 bringing ore and metals from the inside out. 242 00:16:50,007 --> 00:16:53,127 But something didn't add up. 243 00:16:53,127 --> 00:16:56,327 When scientists investigated the rocks around the mine, 244 00:16:56,327 --> 00:16:58,207 they were surprised. 245 00:16:58,207 --> 00:17:02,758 None of the outcrops were typical of the types of rock created by a volcano. 246 00:17:04,447 --> 00:17:07,887 To geologists, it was a hint that the copper and nickel treasures 247 00:17:07,887 --> 00:17:11,596 below the surface were formed by a different process. 248 00:17:14,767 --> 00:17:16,087 They were stumped 249 00:17:16,087 --> 00:17:20,207 until they came across Eugene Shoemaker's work on Meteor Crater. 250 00:17:20,207 --> 00:17:24,847 It made them wonder whether this vast mine could also have been formed 251 00:17:24,847 --> 00:17:26,758 by an asteroid impact. 252 00:17:28,207 --> 00:17:32,917 Could the vast reserves of copper and nickel have arrived from space? 253 00:17:34,047 --> 00:17:36,807 Rocks above ground reveal new evidence. 254 00:17:36,807 --> 00:17:43,167 What we have is a conical type fracture system with these lineations or lines 255 00:17:43,167 --> 00:17:46,127 running through them, and they... they focus down into a point. 256 00:17:46,127 --> 00:17:51,047 These deformed rocks are called shatter cones. 257 00:17:51,047 --> 00:17:54,967 Spray is convinced that the only force powerful enough to deform a rock 258 00:17:54,967 --> 00:17:58,323 into a shatter cone like this would be an asteroid impact. 259 00:17:59,527 --> 00:18:01,167 And these are formed 260 00:18:01,167 --> 00:18:04,047 due to the shockwave interacting with the target rocks, 261 00:18:04,047 --> 00:18:08,647 and they compress the rocks, just like, uh, compressing a spring, 262 00:18:08,647 --> 00:18:10,367 and then, when the shockwave releases, 263 00:18:10,367 --> 00:18:14,047 they form these conical-like structures, which are beautifully shown here. 264 00:18:14,047 --> 00:18:17,967 So these are diagnostic of impact, we can't form them any other way, 265 00:18:17,967 --> 00:18:19,847 you can't form them with dynamite, 266 00:18:19,847 --> 00:18:22,361 you can't even form them with nuclear weapons. 267 00:18:24,167 --> 00:18:26,647 But shatter cones were only a hunch. 268 00:18:26,647 --> 00:18:31,367 Another clue came from the composition of the rock. 269 00:18:31,367 --> 00:18:36,521 It's a mixture of violently broken pieces, fused into melted material. 270 00:18:38,407 --> 00:18:43,727 So what we have here is made up of the debris from the Earth's crust, 271 00:18:43,727 --> 00:18:46,527 blasted into millions of pieces, 272 00:18:46,527 --> 00:18:51,927 and the darker core material may well contain traces 273 00:18:51,927 --> 00:18:55,327 of the meteorite left in it in the form of iridium. 274 00:18:55,327 --> 00:19:00,327 Iridium is one of the rarest metals on the surface of the Earth. 275 00:19:00,327 --> 00:19:05,247 In space, it is a thousand times more abundant. 276 00:19:05,247 --> 00:19:09,927 Asteroids are like space rubble, and their composition varies dramatically. 277 00:19:09,927 --> 00:19:14,807 Some are made of rock-like material, some from metals such as iron, 278 00:19:14,807 --> 00:19:17,887 but they all have one thing in common. 279 00:19:17,887 --> 00:19:22,119 They all contain comparatively large amounts of iridium. 280 00:19:23,127 --> 00:19:25,807 So any high amounts of iridium found on Earth 281 00:19:25,807 --> 00:19:29,117 becomes a fingerprint of an impact event. 282 00:19:30,127 --> 00:19:32,647 So what we're going to do is take a sample and analyse it, 283 00:19:32,647 --> 00:19:36,007 to see if we can find an enriched iridium signature, 284 00:19:36,007 --> 00:19:39,443 which would tell us that we have a particular class of meteorite. 285 00:19:41,007 --> 00:19:45,407 To find iridium, the lab samples of the crushed rock are heated in a furnace 286 00:19:45,407 --> 00:19:49,167 to over a thousand degrees Celsius. 287 00:19:49,167 --> 00:19:53,843 The rock melts and metals in the rock separate out and form a disc. 288 00:19:54,887 --> 00:20:00,280 When the disc cools, it is analysed for traces of iridium. 289 00:20:01,807 --> 00:20:05,087 Hi, John. How's it going? Not so bad. 290 00:20:05,087 --> 00:20:07,247 Metal from the rock is dissolved into liquid. 291 00:20:07,247 --> 00:20:09,767 It is passed through a mass spectrometer 292 00:20:09,767 --> 00:20:13,327 capable of spotting tiny metal parts. 293 00:20:13,327 --> 00:20:18,167 This incredibly accurate device provides the vital piece of evidence. 294 00:20:18,167 --> 00:20:23,367 The blue and red lines show there's ten times more iridium in the Sudbury rocks 295 00:20:23,367 --> 00:20:26,962 than in control samples from normal earth crust. 296 00:20:28,407 --> 00:20:34,642 This is indisputable proof that Sudbury had once been hit by a huge asteroid. 297 00:20:39,727 --> 00:20:42,727 But where was the impact crater? 298 00:20:42,727 --> 00:20:47,407 The landscape here is flat as far as the eye can see. 299 00:20:47,407 --> 00:20:51,687 Scientists believe over millions of years, the crater disappeared. 300 00:20:51,687 --> 00:20:57,407 Erosion wore it down until all that is left is the faint outline of ring structures 301 00:20:57,407 --> 00:21:00,207 seen on satellite images from space. 302 00:21:00,207 --> 00:21:02,847 Spray and his colleagues have surveyed the area 303 00:21:02,847 --> 00:21:07,967 and found that Sudbury is the second biggest impact site on Earth. 304 00:21:07,967 --> 00:21:12,567 155 miles in diameter, that's three quarters of the size 305 00:21:12,567 --> 00:21:16,367 of the world's largest crater at Vredefort in South Africa. 306 00:21:16,367 --> 00:21:20,527 Spray calculated almost two billion years ago, 307 00:21:20,527 --> 00:21:25,521 a space rock the size of Mount Everest must have crashed into Earth here. 308 00:21:29,207 --> 00:21:32,367 When the asteroid hit it produced an instant crater 309 00:21:32,367 --> 00:21:35,757 20 times deeper than the Grand Canyon. 310 00:21:38,447 --> 00:21:41,447 The energy is so intense with the shockwave going back up 311 00:21:41,447 --> 00:21:43,887 through the projectile, the back flows off, 312 00:21:43,887 --> 00:21:47,847 and you end up fragmenting the projectile, the meteorite, 313 00:21:47,847 --> 00:21:51,247 such that you may even end up with pieces of the Sudbury projectile 314 00:21:51,247 --> 00:21:53,247 on the moon, and that's highly likely. 315 00:21:53,247 --> 00:21:55,807 So it actually gets blasted out into space. 316 00:21:57,487 --> 00:21:59,647 But one question remained. 317 00:21:59,647 --> 00:22:03,247 Where did the valuable reserves of nickel and copper come from 318 00:22:03,247 --> 00:22:06,527 that turned Sudbury into a famous mining site? 319 00:22:06,527 --> 00:22:08,887 The asteroid had vapourised, 320 00:22:08,887 --> 00:22:12,721 so the large nickel and copper deposits couldn't have come from space. 321 00:22:14,607 --> 00:22:19,007 When the asteroid hit, it penetrated almost 18 miles into the Earth, 322 00:22:19,007 --> 00:22:21,527 melting a huge cavity into the rock. 323 00:22:21,527 --> 00:22:27,687 Scientists estimate that this giant hole lasted only a short while. 324 00:22:27,687 --> 00:22:31,367 Within hours, it collapsed, because of gravity. 325 00:22:31,367 --> 00:22:35,207 It's just like when you try and dig a hole on the beach in sand with your shovel. 326 00:22:35,207 --> 00:22:38,647 You're spading the sand out and you can only go so big 327 00:22:38,647 --> 00:22:41,607 before the sides actually collapse in. 328 00:22:41,607 --> 00:22:43,087 After the cliffs collapsed, 329 00:22:43,087 --> 00:22:47,647 the crater floor filled up with a deep lake of hot, liquid rock. 330 00:22:47,647 --> 00:22:50,527 The hole had been created in seconds, 331 00:22:50,527 --> 00:22:55,287 but the hot rock took hundreds of thousands of years to cool. 332 00:22:55,287 --> 00:22:58,647 During this time, heavier metals like copper and nickel 333 00:22:58,647 --> 00:23:01,807 naturally present in the liquid rock, sank to the bottom 334 00:23:01,807 --> 00:23:06,244 and formed Sudbury's deposits of precious minerals. 335 00:23:09,527 --> 00:23:14,447 The impact at Sudbury had radically changed the geology of a wide region, 336 00:23:14,447 --> 00:23:18,963 concentrating nickel and copper into awesome mining deposits. 337 00:23:23,327 --> 00:23:27,167 Impact sites were now more than academic interest. 338 00:23:27,167 --> 00:23:31,327 Such rich mineral deposits potentially meant big business 339 00:23:31,327 --> 00:23:33,127 and economic wealth. 340 00:23:33,127 --> 00:23:37,327 Mining companies on the hunt for precious natural resources 341 00:23:37,327 --> 00:23:42,327 now use satellite imagery to reveal new craters around the world. 342 00:23:42,327 --> 00:23:47,959 Rings that can be seen from space suggest giant asteroid impacts. 343 00:23:49,767 --> 00:23:51,847 They know that these impact sites 344 00:23:51,847 --> 00:23:55,920 may contain more than just copper and nickel. 345 00:23:57,407 --> 00:24:01,407 Rich gold mines in South Africa were also thought to have been created 346 00:24:01,407 --> 00:24:03,047 by volcanic processes, 347 00:24:03,047 --> 00:24:07,527 but the discovery of shatter cones in the 1960s and ring structures 348 00:24:07,527 --> 00:24:09,887 seen on satellite images revealed 349 00:24:09,887 --> 00:24:14,727 what is now thought to be the biggest impact crater on the planet. 350 00:24:14,727 --> 00:24:18,127 Here, the impact concentrated valuable minerals in the rock, 351 00:24:18,127 --> 00:24:20,925 this time into precious deposits of gold ore. 352 00:24:22,807 --> 00:24:24,927 And at Chicxulub, Mexico, 353 00:24:24,927 --> 00:24:28,007 scientists discovered traces of a large asteroid impact 354 00:24:28,007 --> 00:24:33,525 that wiped out the entire dinosaur population 65 million years ago. 355 00:24:36,127 --> 00:24:38,087 But recently, scientists have drawn a link 356 00:24:38,087 --> 00:24:41,167 between the massive crater at Chicxulub 357 00:24:41,167 --> 00:24:44,842 and a huge oil reservoir discovered nearby. 358 00:24:46,087 --> 00:24:49,167 As the asteroid crashed into the Earth's crust, 359 00:24:49,167 --> 00:24:53,399 it fractured the underground rock, making it porous. 360 00:24:54,927 --> 00:25:00,167 Oil, abundant in the deeper layers below, rose up and seeped into the porous rock, 361 00:25:00,167 --> 00:25:02,237 creating an oil reservoir. 362 00:25:05,247 --> 00:25:10,807 Now scientists could more easily recognise signs of large impact sites. 363 00:25:10,807 --> 00:25:15,447 Shatter cones were evidence of strong shockwaves. 364 00:25:15,447 --> 00:25:20,527 The presence of the space metal iridium was proof for an asteroid impact, 365 00:25:20,527 --> 00:25:24,047 and satellite imagery has shown how impact craters 366 00:25:24,047 --> 00:25:27,244 can be linked to vast mineral wealth. 367 00:25:28,807 --> 00:25:32,087 Besides the minerals found at different impact sites, 368 00:25:32,087 --> 00:25:35,447 asteroids have left evidence of massive destruction. 369 00:25:35,447 --> 00:25:39,527 And this has led scientists to a terrifying conclusion. 370 00:25:39,527 --> 00:25:43,884 If it has happened in the past, there is little doubt it could happen again. 371 00:25:48,967 --> 00:25:52,087 October 9th, 1992. 372 00:25:52,087 --> 00:25:55,087 Johnstown, Pennsylvania. 373 00:25:55,087 --> 00:25:59,087 Thousands of sports fans were watching their local high school football game 374 00:25:59,087 --> 00:26:01,927 when a dazzling meteor slashed through the skies. 375 00:26:01,927 --> 00:26:06,287 In only a few seconds it travelled over Eastern Kentucky, North Carolina, 376 00:26:06,287 --> 00:26:08,118 Maryland and New Jersey. 377 00:26:09,647 --> 00:26:13,117 It became one of the most filmed fireballs in history. 378 00:26:14,127 --> 00:26:18,607 When it landed in Peekskill, New York, it smashed the trunk of a car. 379 00:26:18,607 --> 00:26:21,807 Luckily, no-one got hurt. 380 00:26:21,807 --> 00:26:27,487 November 20th, 2008, an asteroid struck Earth again. 381 00:26:27,487 --> 00:26:30,727 A mighty fireball streaked over Western Canada. 382 00:26:30,727 --> 00:26:33,727 As it dashed through the skies of Alberta, 383 00:26:33,727 --> 00:26:36,002 it broke into thousands of little pieces. 384 00:26:37,647 --> 00:26:41,845 It is the greatest number of fragments recorded from a single fall. 385 00:26:43,767 --> 00:26:47,647 Each year, almost 4,500 small sized meteorites, 386 00:26:47,647 --> 00:26:50,887 greater than two pounds each, hit Earth. 387 00:26:50,887 --> 00:26:56,047 Over 99% of the impacts stay unnoticed and damage is minimal. 388 00:26:56,047 --> 00:27:00,404 But on rare occasions, asteroids can be devastating. 389 00:27:06,447 --> 00:27:08,247 13,000 years ago. 390 00:27:08,247 --> 00:27:13,241 The great ice sheets were in retreat as the last Ice Age was coming to an end. 391 00:27:16,407 --> 00:27:19,967 The Clovis people, one of the first human inhabitants of North America, 392 00:27:19,967 --> 00:27:23,967 roamed the great plains alongside giant beasts. 393 00:27:23,967 --> 00:27:26,845 (TRUMPETS) 394 00:27:29,127 --> 00:27:32,967 A team of archaeologists is investigating the evidence they left 395 00:27:32,967 --> 00:27:37,207 in the Sheriden Cave in Ohio, southwest of Lake Erie. 396 00:27:37,207 --> 00:27:40,207 Clovis peoples were hunter-gatherers. 397 00:27:40,207 --> 00:27:45,407 In other words, they hunted wild game and they gathered wild plant foods. 398 00:27:45,407 --> 00:27:46,887 At this time period, 399 00:27:46,887 --> 00:27:49,527 there were animals we call the mega-mammals, 400 00:27:49,527 --> 00:27:52,247 which included large elephant-like creatures 401 00:27:52,247 --> 00:27:56,607 such as the woolly mammoth, as well as the American mastodon. 402 00:27:56,607 --> 00:27:59,927 Then, suddenly, all evidence of the mega-mammals 403 00:27:59,927 --> 00:28:02,919 and the weapons used by the Clovis people disappeared. 404 00:28:04,007 --> 00:28:06,527 The same observation was made by geologists 405 00:28:06,527 --> 00:28:10,367 at other excavation sites across America. 406 00:28:10,367 --> 00:28:15,202 Tankersley is convinced a catastrophe drove the mammoths to extinction. 407 00:28:16,567 --> 00:28:20,127 And it would have happened in a snap of a finger, 408 00:28:20,127 --> 00:28:25,207 over 30 genera of mega-mammals went extinct 409 00:28:25,207 --> 00:28:28,438 and the Clovis technology disappeared forever. 410 00:28:29,727 --> 00:28:33,163 Clues to what happened came from another part of the cave. 411 00:28:34,607 --> 00:28:39,167 It's in a geological formation known as the Black Mat layer. 412 00:28:39,167 --> 00:28:42,647 It is a dark line of rock packed with charred debris, 413 00:28:42,647 --> 00:28:46,247 and it suggests a violent death. 414 00:28:46,247 --> 00:28:52,247 The black layer which you see in this profile is carbon, 415 00:28:52,247 --> 00:28:57,727 a high organic content, and what we're seeing is the remains of animals 416 00:28:57,727 --> 00:28:59,567 which were living at that time, 417 00:28:59,567 --> 00:29:03,087 which, literally, had the flesh burned off their bones. 418 00:29:03,087 --> 00:29:06,047 In order to do that, we're talking about somewhere 419 00:29:06,047 --> 00:29:10,007 between 500 and 1,200 degrees Fahrenheit. 420 00:29:10,007 --> 00:29:12,447 The cause of the inferno has long been a mystery, 421 00:29:12,447 --> 00:29:17,167 but, deep in these Ohio caves, Tankersley thinks he has found traces 422 00:29:17,167 --> 00:29:19,407 for an asteroid impact. 423 00:29:19,407 --> 00:29:22,767 This is what's known a magnetic susceptibility meter. 424 00:29:22,767 --> 00:29:27,847 It looks at the degree of magnetism of the layers of the sediments. 425 00:29:27,847 --> 00:29:37,127 If we take a reading, in the layer that predates the asteroid or comet strike, 426 00:29:37,127 --> 00:29:41,207 and we look at the reading, it's somewhere around seven. 427 00:29:41,207 --> 00:29:48,567 If we compare that at the Black Mat, where we're finding micro-meteorites, 428 00:29:48,567 --> 00:29:54,607 we're looking at 50 times the magnetism of the layer before, 429 00:29:54,607 --> 00:29:59,647 we have evidence of an asteroid or a large comet. 430 00:29:59,647 --> 00:30:02,287 Like at Meteor Crater in Arizona, 431 00:30:02,287 --> 00:30:06,207 Tankersley believes the asteroid brought in large amounts of iron, 432 00:30:06,207 --> 00:30:08,198 causing a strong magnetic field. 433 00:30:09,247 --> 00:30:11,687 As the asteroid entered the atmosphere, 434 00:30:11,687 --> 00:30:16,087 it burst into thousands of smaller micro-meteorites. 435 00:30:16,087 --> 00:30:19,407 He believes that the impact annihilated the mega-mammals 436 00:30:19,407 --> 00:30:23,607 and brought the Clovis people to the edge of extinction. 437 00:30:23,607 --> 00:30:28,327 Sceptics within the scientific community doubt the theory. 438 00:30:28,327 --> 00:30:31,607 They think the devastation could have been caused by lightning, 439 00:30:31,607 --> 00:30:35,839 or a wildfire started by the Clovis people themselves. 440 00:30:38,327 --> 00:30:41,127 But recently, further evidence for the destructive power 441 00:30:41,127 --> 00:30:44,119 of these killer rocks has been uncovered. 442 00:30:45,647 --> 00:30:49,887 In March 1994, Carolyn Shoemaker and a team of astronomers 443 00:30:49,887 --> 00:30:52,327 made an extraordinary discovery. 444 00:30:52,327 --> 00:30:54,927 They were observing and recording the night sky 445 00:30:54,927 --> 00:30:58,167 when a giant fireball approached Jupiter. 446 00:30:58,167 --> 00:31:00,167 Here was this fuzzy bar of light, 447 00:31:00,167 --> 00:31:03,247 and I looked at it and thought, "What on Earth? 448 00:31:03,247 --> 00:31:05,727 "It looks like a squashed comet," 449 00:31:05,727 --> 00:31:08,127 because it was fuzzy. 450 00:31:08,127 --> 00:31:12,167 It wasn't quite an asteroid, but a comet with a tail. 451 00:31:12,167 --> 00:31:14,687 Now called Shoemaker-Levy 9, 452 00:31:14,687 --> 00:31:18,127 the comet's mixture of giant space rocks and ice 453 00:31:18,127 --> 00:31:19,958 was heading directly for planet Jupiter. 454 00:31:21,527 --> 00:31:23,087 Very exciting. 455 00:31:23,087 --> 00:31:26,167 We had already been up on a high, 456 00:31:26,167 --> 00:31:30,207 and we went up even farther, because this was so unusual. 457 00:31:30,207 --> 00:31:36,207 No-one had ever seen, actually seen, a comet in orbit about Jupiter, 458 00:31:36,207 --> 00:31:38,727 although we knew they had been there, 459 00:31:38,727 --> 00:31:44,407 no-one had seen a comet impact another body in space. 460 00:31:44,407 --> 00:31:48,487 For the first time, the whole world was watching rogue pieces of rock 461 00:31:48,487 --> 00:31:50,717 hurtling through space towards a planet. 462 00:31:51,967 --> 00:31:55,727 As they entered Jupiter's atmosphere, something incredible happened. 463 00:31:55,727 --> 00:31:59,967 The rogue pieces exploded, causing giant shockwaves. 464 00:31:59,967 --> 00:32:04,927 They left a series of holes in Jupiter, each bigger than the Earth itself. 465 00:32:04,927 --> 00:32:10,807 SHOEMAKER: The impact on Jupiter was sensational, it was very large. 466 00:32:10,807 --> 00:32:16,407 You could see the dark spot, and, you know, you could see the first ring 467 00:32:16,407 --> 00:32:19,207 and then you could see this cloud of dust. 468 00:32:19,207 --> 00:32:22,447 The team had witnessed an air burst. 469 00:32:22,447 --> 00:32:26,647 As the giant fireballs approached Jupiter at high speed, 470 00:32:26,647 --> 00:32:29,927 they were slowed down by the planet's atmosphere. 471 00:32:29,927 --> 00:32:33,167 The energy of motion was converted into pressure and heat 472 00:32:33,167 --> 00:32:37,080 and resulted in a huge explosion. 473 00:32:39,727 --> 00:32:44,847 A similar air burst over Earth would annihilate all life on the planet. 474 00:32:51,007 --> 00:32:52,487 Physicist Mark Boslough works 475 00:32:52,487 --> 00:32:56,887 at the top secret Sandia Research laboratories in New Mexico. 476 00:32:56,887 --> 00:32:59,047 He's one of many defence scientists 477 00:32:59,047 --> 00:33:02,596 investigating the possibilities of such an Armageddon. 478 00:33:07,047 --> 00:33:11,687 Research suggests we might not be as safe as once thought. 479 00:33:11,687 --> 00:33:15,566 The investigation leads to a remote region of Siberia. 480 00:33:17,127 --> 00:33:22,997 On June 30th, 1908, a bright flash streaked through the skies. 481 00:33:24,327 --> 00:33:28,047 Seconds later, the sound of an explosion followed. 482 00:33:28,047 --> 00:33:32,199 The area of Tunguska was hit by an air burst. 483 00:33:34,327 --> 00:33:38,367 A devastating shockwave uprooted thousands of trees 484 00:33:38,367 --> 00:33:42,360 and flattened more than 830 square miles of Taiga forest. 485 00:33:43,727 --> 00:33:47,407 There is still some evidence, um, there are some of these trees 486 00:33:47,407 --> 00:33:50,247 that had all their branches stripped off in 1908, 487 00:33:50,247 --> 00:33:53,007 and those trees that have been dead now for a hundred years 488 00:33:53,007 --> 00:33:54,918 are still standing. 489 00:33:56,127 --> 00:33:59,967 Scientists assumed the destruction must have been caused by an asteroid 490 00:33:59,967 --> 00:34:02,847 of at least 100 feet. 491 00:34:02,847 --> 00:34:06,287 And they also believed asteroids of this size would hit Earth 492 00:34:06,287 --> 00:34:09,687 only once every thousand years. 493 00:34:09,687 --> 00:34:13,487 But, in 2008, Boslough discovered something alarming. 494 00:34:13,487 --> 00:34:16,407 With advanced computer simulation, 495 00:34:16,407 --> 00:34:19,967 he calculated that a small meteorite of only 20 feet across 496 00:34:19,967 --> 00:34:22,322 could cause a Tunguska-like event. 497 00:34:24,047 --> 00:34:27,487 The... the air burst was actually smaller than people have been thinking 498 00:34:27,487 --> 00:34:30,687 for the last, um, 20 years or so. 499 00:34:30,687 --> 00:34:35,247 And the reason we think it was smaller was because of this neglect 500 00:34:35,247 --> 00:34:38,607 of the momentum that continued to carry the energy down. 501 00:34:38,607 --> 00:34:42,487 What I'm showing here is an asteroid coming from the upper right, 502 00:34:42,487 --> 00:34:44,487 and it's pushing down into the atmosphere, 503 00:34:44,487 --> 00:34:47,767 and, about seven and a half miles above the surface, it explodes. 504 00:34:47,767 --> 00:34:50,967 But you can see that it continues to push downwards, 505 00:34:50,967 --> 00:34:53,687 so all that energy is continuing to push downwards, 506 00:34:53,687 --> 00:34:56,687 and it's driving this shockwave ahead of it. 507 00:34:56,687 --> 00:35:01,287 The shockwave is a big blast of air, hurricane-force winds. 508 00:35:01,287 --> 00:35:03,887 Now, that's what blows the trees down. 509 00:35:03,887 --> 00:35:08,727 Based on this theory, asteroids able to cause another Tunguska 510 00:35:08,727 --> 00:35:12,727 could statistically hit our planet every hundred years. 511 00:35:12,727 --> 00:35:16,127 If such an air burst happened over a populated area, 512 00:35:16,127 --> 00:35:18,607 the consequences would be devastating. 513 00:35:18,607 --> 00:35:24,447 Well, if something like this were to hit or explode over the sky of Los Angeles, 514 00:35:24,447 --> 00:35:27,767 it would destroy buildings over that same kind of area, 515 00:35:27,767 --> 00:35:31,047 800 square miles or so, so it could completely wipe out 516 00:35:31,047 --> 00:35:35,006 a large portion of the Los Angeles metropolitan area. 517 00:35:36,767 --> 00:35:39,847 The investigation has revealed that asteroid strikes 518 00:35:39,847 --> 00:35:41,758 can be incredibly destructive. 519 00:35:44,527 --> 00:35:47,767 The Black Mat layer of sediment in the Sheriden Cave in Ohio 520 00:35:47,767 --> 00:35:49,527 is evidence that an asteroid impact 521 00:35:49,527 --> 00:35:54,767 might have led to the extinction of the mega-mammals. 522 00:35:54,767 --> 00:35:58,127 An explosion of a giant fireball in Jupiter's atmosphere 523 00:35:58,127 --> 00:36:03,076 showed scientists, in real time, the destructive power of air bursts. 524 00:36:04,567 --> 00:36:07,687 And an air burst over Siberia leads to evidence 525 00:36:07,687 --> 00:36:12,477 that a meteorite as small as 20 feet across can cause massive devastation. 526 00:36:14,487 --> 00:36:19,247 The powerful force of an asteroid is evident, but the story doesn't end here. 527 00:36:19,247 --> 00:36:23,087 The actual asteroid rocks, when examined, 528 00:36:23,087 --> 00:36:27,877 reveal extraordinary secrets about the beginnings of our solar system. 529 00:36:35,087 --> 00:36:40,525 Asteroids plunging from space have transformed the surface of our planet. 530 00:36:41,927 --> 00:36:45,727 But there was one thing scientists still had to investigate. 531 00:36:45,727 --> 00:36:49,447 The leftover pieces of the asteroid rocks themselves. 532 00:36:49,447 --> 00:36:54,287 They contain valuable information about the origins of our solar system 533 00:36:54,287 --> 00:36:56,562 and the formation of planet Earth. 534 00:36:58,327 --> 00:37:01,607 But this presents geologists with a problem. 535 00:37:01,607 --> 00:37:05,447 Most giant asteroids vapourise when they impact Earth, 536 00:37:05,447 --> 00:37:08,487 destroying much of their hidden evidence. 537 00:37:08,487 --> 00:37:12,367 Geologists had to search for smaller pieces of broken asteroids, 538 00:37:12,367 --> 00:37:14,087 called meteorites, instead. 539 00:37:14,087 --> 00:37:15,767 (OSCILLATING TONE) 540 00:37:15,767 --> 00:37:19,767 With little weight, these rocks survive the fiery plunge 541 00:37:19,767 --> 00:37:24,687 through the Earth's atmosphere, and land intact on the planet's surface. 542 00:37:24,687 --> 00:37:26,087 (CRACKLING AND BLEEPING) 543 00:37:26,087 --> 00:37:28,927 Geoff Notkin and his group are hunting meteorites 544 00:37:28,927 --> 00:37:32,047 in a dried-up riverbed in Arizona. 545 00:37:32,047 --> 00:37:34,407 They are scanning the ground with metal detectors, 546 00:37:34,407 --> 00:37:38,195 hoping the signals they are getting lead them to iron meteorites. 547 00:37:40,167 --> 00:37:45,007 For the most part, they find iron dust, small magnetic particles from space, 548 00:37:45,007 --> 00:37:47,687 which stick to the magnetic hammer. 549 00:37:47,687 --> 00:37:53,087 The estimate is thousands of tons of meteorites fall on the Earth every year, 550 00:37:53,087 --> 00:37:57,327 but most of those, the vast majority, are tiny dust-sized particles 551 00:37:57,327 --> 00:38:00,444 that collect over the surface of the Earth and are never noticed. 552 00:38:02,247 --> 00:38:05,567 What Notkin is really seeking is not space dust 553 00:38:05,567 --> 00:38:09,407 but extremely valuable pieces of rock from outer space. 554 00:38:09,407 --> 00:38:12,887 He has been hunting meteorites for over 15 years 555 00:38:12,887 --> 00:38:16,727 and has built up a collection of over several hundred samples. 556 00:38:16,727 --> 00:38:19,047 There are three basic types of meteorites. 557 00:38:19,047 --> 00:38:21,927 The irons, which are my favourite, 558 00:38:21,927 --> 00:38:27,127 which are what most people imagine a meteorite really looks like, 559 00:38:27,127 --> 00:38:32,567 and they frequently have very attractive aesthetic surface features 560 00:38:32,567 --> 00:38:36,887 like this piece, caused by melting in the atmosphere. 561 00:38:36,887 --> 00:38:38,527 The next group are stones, 562 00:38:38,527 --> 00:38:42,087 and these are fairly similar to... at least, in appearance, 563 00:38:42,087 --> 00:38:43,647 to terrestrial rocks, 564 00:38:43,647 --> 00:38:47,847 although they contain chondrules and iron and nickel from outer space, 565 00:38:47,847 --> 00:38:49,847 which we don't find in Earth rocks. 566 00:38:49,847 --> 00:38:53,647 And the third group, the stony irons, is the rarest of the three, 567 00:38:53,647 --> 00:38:55,247 and also the most valuable. 568 00:38:55,247 --> 00:38:59,647 Um, the value on something like this would be at least 25 to 30,000 dollars. 569 00:38:59,647 --> 00:39:03,687 And if we were to take this piece and cut it open, 570 00:39:03,687 --> 00:39:07,767 we would reveal this beautiful interior, olivine crystals, 571 00:39:07,767 --> 00:39:12,045 and they're known popularly as the semi-precious gemstone peridot. 572 00:39:15,567 --> 00:39:19,727 Monetary value aside, to geologists like Minnie Wadhwa, 573 00:39:19,727 --> 00:39:23,561 these meteorites are a window into the Earth's ancient past. 574 00:39:26,967 --> 00:39:30,807 At Arizona State University, she runs a department analysing 575 00:39:30,807 --> 00:39:34,322 some of the oldest meteorite rocks that landed on Earth. 576 00:39:36,287 --> 00:39:37,887 This meteorite right here, 577 00:39:37,887 --> 00:39:41,767 this carbon-rich chondrite, uh, 578 00:39:41,767 --> 00:39:45,047 this probably is a close proxy of the kinds of materials 579 00:39:45,047 --> 00:39:48,087 that were bombarding the early Earth, and they're called chondrites 580 00:39:48,087 --> 00:39:52,567 because they've got these tiny little inclusions, spherical inclusions in them 581 00:39:52,567 --> 00:39:56,167 called chondrules, which are amongst, uh, some of the earliest solids 582 00:39:56,167 --> 00:39:58,527 that formed in our solar system. 583 00:39:58,527 --> 00:40:02,727 In the beginnings of our solar system, there was nothing but gas and dust. 584 00:40:02,727 --> 00:40:06,927 As it cooled, solid asteroid rocks began to form. 585 00:40:06,927 --> 00:40:12,327 With modern technology, scientists have been able to pinpoint their exact age. 586 00:40:12,327 --> 00:40:17,167 Most meteorites are thought to have formed 4.6 billion years ago, 587 00:40:17,167 --> 00:40:20,687 but, um, modern techniques have now made it possible for us 588 00:40:20,687 --> 00:40:23,767 to actually age-date meteorites with much greater precision, 589 00:40:23,767 --> 00:40:28,327 and we now know, by looking at meteorites like this one, for example, uh, 590 00:40:28,327 --> 00:40:33,687 that, in fact, the solar system was formed 4.567 billion years ago. 591 00:40:33,687 --> 00:40:37,167 And we know that date, uh, within a million years or so. 592 00:40:37,167 --> 00:40:39,687 So, essentially, we can very precisely age-date the formation 593 00:40:39,687 --> 00:40:42,167 of our solar system by looking at meteorites. 594 00:40:42,167 --> 00:40:44,927 As the meteorite rocks floated in early space, 595 00:40:44,927 --> 00:40:47,927 they collided and grew into bigger bodies. 596 00:40:47,927 --> 00:40:53,287 These ancient rocks were the building blocks of planets, including early Earth. 597 00:40:53,287 --> 00:40:55,487 By looking at these types of meteorites, 598 00:40:55,487 --> 00:40:59,807 we can actually begin to understand how our own Earth might have formed, 599 00:40:59,807 --> 00:41:04,007 and, uh, what kinds of processes might have happened on the early Earth, 600 00:41:04,007 --> 00:41:07,807 because we actually get to look at, uh, the deep interiors 601 00:41:07,807 --> 00:41:09,327 of small planetary bodies 602 00:41:09,327 --> 00:41:11,397 when we're actually looking at some of these meteorites. 603 00:41:15,327 --> 00:41:19,047 After the planets formed, the rubble which was left accumulated 604 00:41:19,047 --> 00:41:23,567 and formed a cloud of dust and rock between Mars and Jupiter. 605 00:41:23,567 --> 00:41:27,003 This is called the asteroid belt. 606 00:41:28,167 --> 00:41:30,727 Every now and then, one of these rocks breaks free 607 00:41:30,727 --> 00:41:35,327 and tumbles through space at 25,000 miles an hour. 608 00:41:35,327 --> 00:41:38,447 When it drops through the atmosphere and lands, 609 00:41:38,447 --> 00:41:43,447 it delivers priceless information about conditions on the early Earth. 610 00:41:43,447 --> 00:41:48,043 Perhaps even hints as to how life itself began. 611 00:41:49,927 --> 00:41:53,847 In the late 1960s, a remarkable fall of meteorites 612 00:41:53,847 --> 00:41:56,927 hit the town of Murchison in Australia. 613 00:41:56,927 --> 00:41:59,527 Scientists around the world took notice. 614 00:41:59,527 --> 00:42:03,407 Well, basically, it consists of silicate minerals, about... 615 00:42:03,407 --> 00:42:07,487 Hundreds of pieces fell from space, greeting the residents of Murchison 616 00:42:07,487 --> 00:42:10,763 with a pungent smell of rotting organic material. 617 00:42:11,767 --> 00:42:16,287 If you open up this... this jar of... of closed Murchison and smell it, 618 00:42:16,287 --> 00:42:21,647 it actually smells, uh, very strongly of sort of volatile organic-rich compounds 619 00:42:21,647 --> 00:42:24,844 that are being de-gassed from this particular rock even today. 620 00:42:25,847 --> 00:42:27,807 Professor Wadhwa and her department 621 00:42:27,807 --> 00:42:31,047 began analysing the Murchison Meteorite. 622 00:42:31,047 --> 00:42:35,967 Incredibly, they found it contained organic compounds called amino acids. 623 00:42:35,967 --> 00:42:40,563 These complex molecules are essential to all life. 624 00:42:42,487 --> 00:42:46,847 The organic materials in this type of meteorite, 625 00:42:46,847 --> 00:42:52,367 uh, were actually the building blocks of... of life as we know it today. 626 00:42:52,367 --> 00:42:57,600 This is the raw material from which, uh, life began on our own planet. 627 00:43:00,527 --> 00:43:04,367 It's possible that the seeds of life arrived from space, 628 00:43:04,367 --> 00:43:07,767 flown in by asteroids and meteorites. 629 00:43:07,767 --> 00:43:10,167 In the case of our own origins, 630 00:43:10,167 --> 00:43:14,287 it's not absolutely clear that we need of necessarily originated on Earth. 631 00:43:14,287 --> 00:43:17,367 The seeds of our life and the very primitive life forms 632 00:43:17,367 --> 00:43:19,207 could have actually come from another planet 633 00:43:19,207 --> 00:43:20,686 or even another solar system. 634 00:43:26,687 --> 00:43:30,927 New insights into asteroid impacts has revolutionised our understanding 635 00:43:30,927 --> 00:43:33,760 of how the Earth was made. 636 00:43:35,327 --> 00:43:40,321 Overturned rock beds around Meteor Crater were clues for a massive impact. 637 00:43:42,247 --> 00:43:43,767 Advanced computer modelling 638 00:43:43,767 --> 00:43:47,442 shows how asteroid rocks are vapourised after impact. 639 00:43:49,247 --> 00:43:53,927 Traces of iridium in the rocks in Sudbury were evidence for an asteroid impact 640 00:43:53,927 --> 00:43:56,157 that concentrated precious metals. 641 00:43:58,847 --> 00:44:02,727 From meteorites landing on Earth, scientists were able to calculate 642 00:44:02,727 --> 00:44:07,755 that our solar system formed exactly 4.567 billion years ago. 643 00:44:09,207 --> 00:44:13,847 And the analysis of these space rocks showed that the organic seeds of life 644 00:44:13,847 --> 00:44:19,407 had perhaps arrived on Earth, flown in from space. 645 00:44:19,407 --> 00:44:21,847 Asteroid impacts profoundly shaped 646 00:44:21,847 --> 00:44:24,367 the geology of our Earth. 647 00:44:24,367 --> 00:44:25,567 But as examples 648 00:44:25,567 --> 00:44:26,807 from the past have shown, 649 00:44:26,807 --> 00:44:28,287 they have the power 650 00:44:28,287 --> 00:44:31,916 to annihilate our entire planet in an instant.