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These are the user uploaded subtitles that are being translated: 1 00:00:04,300 --> 00:00:05,950 The Grand Canyon- 2 00:00:06,000 --> 00:00:11,050 a colossal labyrinth of towering buttes and deep sided canyons. 3 00:00:11,100 --> 00:00:12,850 For over a century, 4 00:00:12,900 --> 00:00:16,350 scientists have puzzled over how one small river 5 00:00:16,400 --> 00:00:19,850 could cut such a deep slice through the earth. 6 00:00:20,600 --> 00:00:24,650 The Grand Canyon formed through processes deep within the earth 7 00:00:24,700 --> 00:00:27,050 invisible to the eye. 8 00:00:27,100 --> 00:00:30,950 Today new discoveries point towards new answers- 9 00:00:31,000 --> 00:00:34,950 Scientists are on the brink of understanding the geological forces 10 00:00:35,000 --> 00:00:41,150 that created one of the natural wonders of the world- the Grand Canyon. 11 00:00:58,800 --> 00:01:04,250 It's a landmark so immense that you can see it from space. 12 00:01:05,700 --> 00:01:13,050 277 miles long, up to 18 miles wide and one mile deep- 13 00:01:13,100 --> 00:01:17,050 The Grand Canyon is one of the deepest chasms on Earth. 14 00:01:17,100 --> 00:01:20,350 Its walls plunge sheer into the Earth's crust. 15 00:01:24,300 --> 00:01:31,250 The Colorado River sliced through 2 billion years of our planet's history in less than 5 million years, 16 00:01:31,300 --> 00:01:35,150 exposing layer after layer of geological time. 17 00:01:36,400 --> 00:01:39,950 The first humans walked here thousands of years ago. 18 00:01:40,000 --> 00:01:43,550 Since then the canyon has inspired awe. 19 00:01:44,900 --> 00:01:46,750 How did it come to be here 20 00:01:46,800 --> 00:01:50,050 and what secrets lie hidden in its walls? 21 00:01:50,700 --> 00:01:54,250 To many Native Americans this land is sacred. 22 00:01:54,300 --> 00:01:57,150 They have revered the canyon for centuries. 23 00:01:57,200 --> 00:02:00,850 The canyon is a very spiritual and powerful place. 24 00:02:00,900 --> 00:02:05,150 Our legends say that we actually came from the bottom of the canyon. 25 00:02:05,300 --> 00:02:08,850 Scientists like senior geologist John Spencer 26 00:02:08,900 --> 00:02:12,150 consider the Canyon a treasure- and a mystery. 27 00:02:12,200 --> 00:02:16,050 It's a bit startling, because all around it it's very flat 28 00:02:16,100 --> 00:02:18,850 and you can be 100 feet from the edge of the canyon 29 00:02:18,900 --> 00:02:21,250 and think this is a rather boring landscape 30 00:02:21,300 --> 00:02:23,550 And then you walk over and look into the canyon 31 00:02:23,600 --> 00:02:27,350 and all of a sudden there's this monster canyon in front of you 32 00:02:30,000 --> 00:02:36,150 The layers of rock in the canyon walls formed over thousands of millions of years 33 00:02:38,200 --> 00:02:42,450 The deeper you go, the further back in time you travel. 34 00:02:42,700 --> 00:02:48,550 At the top the newest rocks, at the bottom the oldest. 35 00:02:49,700 --> 00:02:53,350 The Grand Canyon appears to be upside down. 36 00:02:53,400 --> 00:02:56,650 On top, fossils from an ancient sea. 37 00:02:58,400 --> 00:03:02,550 At the bottom, remains of an old mountain range. 38 00:03:03,900 --> 00:03:08,450 Karl Karlstrom, geology professor at the University of New Mexico 39 00:03:08,500 --> 00:03:13,550 is an expert on the oldest rocks of the canyon- one mile down. 40 00:03:13,600 --> 00:03:18,350 They reveal what the Southwestern US looked like two billion years ago. 41 00:03:19,400 --> 00:03:23,650 We were interested in what's the oldest chapter of Grand Canyon history. 42 00:03:23,700 --> 00:03:26,950 And these rocks are so spectacularly exposed 43 00:03:27,000 --> 00:03:32,050 that we have the opportunity to study the earliest history in the Grand Canyon. 44 00:03:35,400 --> 00:03:38,450 What's strange about these rocks at the bottom 45 00:03:38,500 --> 00:03:41,650 is that they are part of an ancient mountain range- 46 00:03:41,700 --> 00:03:44,750 now buried under thousands of feet of rock. 47 00:03:45,200 --> 00:03:49,050 They are the remains of a range called the Vishnu Schist, 48 00:03:49,100 --> 00:03:55,050 a layer of metamorphosed rock that dates from around 1.7 billion years ago. 49 00:03:56,400 --> 00:03:58,750 The human eye sees a line of rock. 50 00:03:58,800 --> 00:04:04,750 Karlstrom's instruments see evidence of a mountain range that once towered six miles above. 51 00:04:05,400 --> 00:04:08,750 His techniques bring the past back to life 52 00:04:09,000 --> 00:04:14,750 His clue is the minerals in the rocks that change chemical composition under pressure. 53 00:04:14,800 --> 00:04:18,650 More rock on top means more pressure on the rock below. 54 00:04:19,300 --> 00:04:24,250 This forces a mineral in the rock, garnet, to take up more calcium. 55 00:04:24,300 --> 00:04:27,350 The higher the calcium concentration within the garnet 56 00:04:27,400 --> 00:04:30,450 the brighter it looks under a microscope. 57 00:04:30,500 --> 00:04:34,350 This tells scientists how deep a rock was buried. 58 00:04:34,400 --> 00:04:38,650 We have learned that these rocks were buried to great depth 59 00:04:38,700 --> 00:04:42,950 and the amount of pressure that they experienced 60 00:04:43,000 --> 00:04:47,050 was equivalent to about six miles of rock above them. 61 00:04:49,800 --> 00:04:52,950 Karlstrom's findings have helped other geologists 62 00:04:53,000 --> 00:04:58,250 visualise how this area may have looked 1.7 billion years ago. 63 00:05:00,400 --> 00:05:06,050 Ron Blakey is a professor of geology at Northern Arizona University in Flagstaff. 64 00:05:06,400 --> 00:05:08,250 He studies ancient continents 65 00:05:08,300 --> 00:05:12,550 and discovered that California wasn't always America's West coast. 66 00:05:12,600 --> 00:05:15,950 It's very likely that the coastline of North America 67 00:05:16,000 --> 00:05:19,350 at this period of time was just south of Wyoming, 68 00:05:19,400 --> 00:05:22,150 perhaps along the Wyoming/Colorado border 69 00:05:22,200 --> 00:05:28,550 and extended up into the Lake Superior region and then up into Canada. 70 00:05:28,600 --> 00:05:33,350 So I would say that perhaps only half to two thirds of North America 71 00:05:33,400 --> 00:05:35,550 had been built at that period of time. 72 00:05:44,000 --> 00:05:48,250 The Vishnu mountains stretched across a very different landscape- 73 00:05:48,300 --> 00:05:53,050 the south of North America did not exist as we know it today. 74 00:05:53,900 --> 00:05:58,250 The mountains towered up out of an ocean along the ancient coast. 75 00:05:59,200 --> 00:06:02,150 They eventually became part of the North American continent 76 00:06:02,200 --> 00:06:05,750 and formed the basement rocks of the Grand Canyon. 77 00:06:05,800 --> 00:06:09,150 I imagine it looked like a bit of a train wreck 78 00:06:09,200 --> 00:06:14,750 where each of these island chains was perched offshore. 79 00:06:14,900 --> 00:06:19,550 A series of island chains that had substantial mountains 80 00:06:19,600 --> 00:06:23,750 but fairly high peaks like in the Aleutians 81 00:06:23,800 --> 00:06:27,450 Six miles beneath the summits of these mountainous islands, 82 00:06:27,500 --> 00:06:31,450 the rocks were developing that distinctive calcium signature. 83 00:06:33,100 --> 00:06:35,650 The mountains above didn't last long. 84 00:06:35,700 --> 00:06:38,050 In around 500 million years, 85 00:06:38,100 --> 00:06:40,350 erosion ground them down 86 00:06:40,400 --> 00:06:43,650 until all that was left was this at the bottom- 87 00:06:43,700 --> 00:06:46,650 the Grand Canyon's most ancient layer. 88 00:06:48,300 --> 00:06:50,950 As we rise up the side of the canyon, 89 00:06:51,000 --> 00:06:53,150 we travel forward in time. 90 00:06:53,300 --> 00:06:56,450 Each foot takes us closer to the present day- 91 00:06:56,500 --> 00:06:59,650 and each period has its own history. 92 00:07:01,300 --> 00:07:07,050 Over hundreds of millions of years the landmasses continually change shape. 93 00:07:10,100 --> 00:07:14,250 Forces deep inside the earth cause continents to break apart, 94 00:07:14,300 --> 00:07:17,450 drift away and form new ones. 95 00:07:17,500 --> 00:07:20,550 Deep trenches open up beneath the ocean 96 00:07:20,800 --> 00:07:25,550 Sea levels change and flood low-lying areas. 97 00:07:26,300 --> 00:07:29,550 At least eight separate seas have flooded this area 98 00:07:29,600 --> 00:07:32,550 since erosion cut down the Vishnu Mountains. 99 00:07:33,700 --> 00:07:37,650 They covered the land, stayed for a few million years 100 00:07:37,700 --> 00:07:40,050 and retreated again. 101 00:07:41,000 --> 00:07:42,950 The evidence is here- 102 00:07:43,000 --> 00:07:47,250 nearly two and a half thousand feet above the modern Colorado River 103 00:07:47,300 --> 00:07:51,450 and five and a half thousand feet above present-day sea level... 104 00:07:52,200 --> 00:07:54,650 These are the remains of oyster beds 105 00:07:54,700 --> 00:07:58,450 that flourished here nearly 100 million years ago. 106 00:07:59,900 --> 00:08:04,950 The Cretaceous sea stretched from Kansas in the east to Nevada in the west, 107 00:08:05,000 --> 00:08:08,750 from Mexico in the south to the Arctic in the north. 108 00:08:08,800 --> 00:08:13,150 It was a shallow seaway that covered much of the continent. 109 00:08:13,400 --> 00:08:16,050 Sea creatures sank to the bottom of the ocean 110 00:08:16,100 --> 00:08:19,350 and fossilized in a thick, grey layer of mud. 111 00:08:20,000 --> 00:08:23,350 Scientists call it the Tropic Shale. 112 00:08:25,200 --> 00:08:29,350 Wayne Ranney is fascinated by this region, rich in fossils. 113 00:08:29,400 --> 00:08:32,650 It gives him a clear idea of this area's history. 114 00:08:33,500 --> 00:08:36,350 This oyster bed, which contains millions of oysters 115 00:08:36,400 --> 00:08:40,750 is from a sea that was a shallow sea that covered the interior of North America 116 00:08:40,800 --> 00:08:43,650 between about 80 and 90 million years ago 117 00:08:44,200 --> 00:08:48,150 Oysters weren't the only creatures living in this ancient sea. 118 00:08:48,300 --> 00:08:49,850 Life was abundant. 119 00:08:49,900 --> 00:08:54,650 Sharks, turtles and ammonites also inhabited the waters. 120 00:08:55,700 --> 00:08:59,750 Today, as erosion slowly wears away the layers of rock, 121 00:08:59,900 --> 00:09:02,050 new fossils appear. 122 00:09:02,800 --> 00:09:04,650 And in 2005, 123 00:09:04,700 --> 00:09:08,050 just 70 miles away from the edge of the canyon, 124 00:09:08,100 --> 00:09:12,750 palaeontologists found the well-preserved skeleton of a plesiosaur... 125 00:09:12,800 --> 00:09:15,750 a dinosaur-like, fish-eating reptile. 126 00:09:16,700 --> 00:09:19,950 For David Gillette it was a dream come true. 127 00:09:20,000 --> 00:09:26,050 He is a curator of palaeontology at the Museum of Northern Arizona in Flagstaff. 128 00:09:26,300 --> 00:09:29,250 For a vertebrate palaeontologist, like myself, 129 00:09:29,300 --> 00:09:33,050 finding plesiosaur skeletons like we're finding in the Tropic Shale, 130 00:09:33,100 --> 00:09:35,650 is almost a once in a lifetime experience 131 00:09:35,700 --> 00:09:40,650 The one in front of me was a plesiosaur that was about half-complete, 132 00:09:40,700 --> 00:09:42,850 we found the front half of the body 133 00:09:42,900 --> 00:09:46,850 and that's more exciting almost than anything I can imagine. 134 00:09:46,900 --> 00:09:49,650 Plesiosaurs were sea-going reptiles. 135 00:09:49,700 --> 00:09:53,250 They were last seen about 65 million years ago 136 00:09:53,300 --> 00:09:56,450 when a catastrophic mass extinction hit the earth. 137 00:09:58,700 --> 00:10:01,950 Gillette's Plesiosaur dates back much earlier. 138 00:10:02,400 --> 00:10:04,850 It lived around 90 million years ago. 139 00:10:05,800 --> 00:10:10,050 Clear proof that this area was under the sea at that time. 140 00:10:11,700 --> 00:10:17,350 The seas left deposits of mud, sand and the remains of living creatures. 141 00:10:17,900 --> 00:10:21,050 Sea currents moved this material which then settled. 142 00:10:22,800 --> 00:10:27,550 And over time the deposits turned into layers of sedimentary rock. 143 00:10:27,800 --> 00:10:29,950 Ron Blakey explains. 144 00:10:30,300 --> 00:10:33,150 What I am going to show you now is a form of sedimentation. 145 00:10:34,100 --> 00:10:38,150 I have here a glass cylinder that's filled with water and sediment, mostly sand 146 00:10:38,400 --> 00:10:40,650 and what I'm gonna do is shake this up, 147 00:10:40,700 --> 00:10:42,850 and the shaking up provides energy 148 00:10:42,900 --> 00:10:47,550 that allows the sand grains to move around this cylinder of water, 149 00:10:47,900 --> 00:10:51,650 and then when I set it down that energy is removed 150 00:10:51,700 --> 00:10:54,050 and the grains will immediately settle out. 151 00:10:54,100 --> 00:10:55,250 Let's see what happens... 152 00:11:00,400 --> 00:11:03,150 As you can see the coarsest grains have already settled out 153 00:11:03,200 --> 00:11:06,050 and finer grains and finer grains are settling, 154 00:11:06,600 --> 00:11:08,750 and now most of the sand is out, 155 00:11:08,800 --> 00:11:10,250 the water is still cloudy 156 00:11:10,300 --> 00:11:14,350 because there is some fine material still in suspension within this cylinder. 157 00:11:14,400 --> 00:11:17,050 But all the energy of the system has been removed 158 00:11:17,100 --> 00:11:22,950 and so now even the finest grains over time will settle out to form a layer of sediment 159 00:11:23,900 --> 00:11:28,750 This process demonstrates how sedimentary layers built the Grand Canyon 160 00:11:28,900 --> 00:11:33,450 Over the course of time, the glass cylinder turned many times. 161 00:11:33,500 --> 00:11:37,950 And when the seas come and go this is all that remains. 162 00:11:38,000 --> 00:11:41,150 Millions upon millions of years of sediment 163 00:11:41,200 --> 00:11:44,550 compressed over time to form layers of rock- 164 00:11:44,600 --> 00:11:46,750 the building blocks of the Canyon. 165 00:11:46,900 --> 00:11:50,650 But powerful forces were building deep underground. 166 00:11:50,700 --> 00:11:54,850 Forces that would thrust these rocks a mile into the sky. 167 00:11:57,700 --> 00:12:04,050 We are on a journey to discover the geological processes that created the Grand Canyon 168 00:12:04,100 --> 00:12:06,250 We are in the cretaceous period- 169 00:12:06,300 --> 00:12:09,350 where plesiosaurs hunted in the shallow seas 170 00:12:09,400 --> 00:12:13,050 that covered the area near to where the Grand Canyon is now. 171 00:12:13,100 --> 00:12:17,750 Seas flooded and retreated over this area for millions of years, 172 00:12:17,800 --> 00:12:23,350 overlaying the ancient Vishnu Mountains with two miles of sedimentary rock. 173 00:12:24,300 --> 00:12:27,050 Half of that has since eroded away, 174 00:12:27,100 --> 00:12:31,050 to leave today's canyon, one mile deep. 175 00:12:33,900 --> 00:12:39,950 The next major transformation will push the land several thousand feet into the air. 176 00:12:40,800 --> 00:12:44,650 Deep beneath the earth a monumental force builds up. 177 00:12:45,700 --> 00:12:48,250 It is one of the greatest forces on earth- 178 00:12:48,300 --> 00:12:52,050 the gigantic power of colliding tectonic plates. 179 00:12:55,200 --> 00:12:58,850 Over millions of years the planet's surface changes. 180 00:12:58,900 --> 00:13:03,750 Scientists explain the process using the theory of plate tectonics. 181 00:13:06,500 --> 00:13:10,750 The surface of the earth is made up of a series of large plates. 182 00:13:11,200 --> 00:13:15,750 They float on the soft, plastic part of the earth's mantle. 183 00:13:16,200 --> 00:13:20,750 The inner core of the earth may reach over 12,000 degrees. 184 00:13:21,300 --> 00:13:25,750 Heat escaping from the core creates convection currents in the next layer- 185 00:13:25,800 --> 00:13:27,350 the lower mantle- 186 00:13:27,600 --> 00:13:31,050 pushing the plates slowly across the surface. 187 00:13:31,400 --> 00:13:34,250 Scientists call it continental drift. 188 00:13:34,300 --> 00:13:39,450 Over time, whole plates move apart and crash back into each other, 189 00:13:39,500 --> 00:13:42,750 shaping and reshaping our world. 190 00:13:45,000 --> 00:13:48,550 Scientists believe that these colliding tectonic plates 191 00:13:48,600 --> 00:13:51,750 were instrumental in creating the Grand Canyon. 192 00:13:51,900 --> 00:13:54,850 Around 130 million years ago 193 00:13:54,900 --> 00:14:00,750 the oceanic plate began to collide into the western edge of the North American plate. 194 00:14:03,100 --> 00:14:08,850 Oceanic plates are 30-60 miles thick and lie beneath the sea. 195 00:14:09,500 --> 00:14:13,250 They consist of dense basalt and get pushed down. 196 00:14:14,100 --> 00:14:17,150 Continenal Plates are mostly granite and lighter. 197 00:14:17,200 --> 00:14:21,550 Oceanic plates subduct underneath them when they collide. 198 00:14:22,300 --> 00:14:26,050 So when the oceanic plate hit the lighter north American plate, 199 00:14:26,100 --> 00:14:30,150 the oceanic plate moved under the west coast of America. 200 00:14:32,400 --> 00:14:37,750 Over tens of millions of years the continental crust compressed and thickened 201 00:14:37,900 --> 00:14:40,650 As the oceanic plate thrust downwards, 202 00:14:40,700 --> 00:14:44,750 the whole of the west of America lifted slowly upward. 203 00:14:44,800 --> 00:14:48,250 As the land rose, the sea retreated, 204 00:14:48,300 --> 00:14:51,450 creating the landmass we see today. 205 00:14:52,800 --> 00:14:57,050 The collision dragged down portions of the leading edge of the continental crust. 206 00:14:57,300 --> 00:14:59,550 Beneath the surface it melted 207 00:14:59,600 --> 00:15:02,350 and liquid rock pushed up through the crust. 208 00:15:02,600 --> 00:15:05,550 The Rocky Mountains formed in the north 209 00:15:06,400 --> 00:15:12,550 In the south a range of ancient mountains the Mogollan Highlands grew higher. 210 00:15:14,500 --> 00:15:17,850 The area that today is the Colorado Plateau 211 00:15:17,900 --> 00:15:19,650 rose about one mile, 212 00:15:19,700 --> 00:15:23,750 lifting the ancient sea floor to where it is today- 213 00:15:23,800 --> 00:15:27,550 seven thousand feet above our present sea level. 214 00:15:30,200 --> 00:15:32,850 So what do we see when we look in the Grand Canyon? 215 00:15:34,200 --> 00:15:38,750 When we have marine rocks now exposed at seven thousand feet above sea level 216 00:15:38,800 --> 00:15:41,050 there is a big question here, 217 00:15:41,800 --> 00:15:46,150 did the sea fall that far or was the land uplifted that far? 218 00:15:46,400 --> 00:15:50,950 Well clearly after the marine rocks were deposited in the sea 219 00:15:51,000 --> 00:15:53,250 that formed the rim of the Grand Canyon, 220 00:15:53,300 --> 00:15:55,450 the area had to be uplifted. 221 00:15:57,900 --> 00:16:01,850 The region of the Grand Canyon was now high above sea level. 222 00:16:02,000 --> 00:16:05,350 But at this point it was an unbroken plain. 223 00:16:05,400 --> 00:16:07,450 There was no canyon. 224 00:16:09,000 --> 00:16:14,350 Making the canyon took another force of nature- erosion. 225 00:16:14,400 --> 00:16:16,350 Even as the land rose up, 226 00:16:16,400 --> 00:16:21,250 a river flowed across the plain, and began to cut down through the rock 227 00:16:22,500 --> 00:16:24,850 Here we have a colourful layer cake, 228 00:16:24,900 --> 00:16:29,050 which represents the rock formations on the Colorado Plateau in the Grand Canyon region 229 00:16:29,100 --> 00:16:32,350 and the river itself is represented by this knife. 230 00:16:32,400 --> 00:16:35,450 Now as the Colorado Plateau is uplifted 231 00:16:35,500 --> 00:16:39,450 the river chisels its way down through and actually makes a cut, 232 00:16:39,800 --> 00:16:43,550 which is... I made a canyon. 233 00:16:44,400 --> 00:16:46,250 70 million years ago 234 00:16:46,300 --> 00:16:49,950 water and snowmelt flowed from the Mogollan highlands 235 00:16:50,000 --> 00:16:53,450 onto the surface of the future Colorado Plateau. 236 00:16:53,500 --> 00:16:56,750 They began slowly cutting into the plateau area. 237 00:16:57,500 --> 00:17:00,150 Ron Blakey demonstrates how flowing water 238 00:17:00,200 --> 00:17:04,750 can cut through the layers of sedimentary rock to make a canyon. 239 00:17:04,800 --> 00:17:07,350 When I cut a hole in the side of the tub 240 00:17:07,400 --> 00:17:11,150 we are going to see the sediment is going to be eroded. 241 00:17:11,200 --> 00:17:12,950 Let's see if this works. 242 00:17:14,700 --> 00:17:17,950 There you can see the erosion taking place. 243 00:17:18,000 --> 00:17:20,350 As I lower the base level 244 00:17:20,900 --> 00:17:23,650 by cutting a part of the plastic tub 245 00:17:23,700 --> 00:17:28,050 you can see the water coming down through the sediment and exposing it. 246 00:17:29,100 --> 00:17:31,350 So if erosion cut through the rock 247 00:17:31,400 --> 00:17:36,850 the next part of the puzzle is to find the ancient river that created the canyon. 248 00:17:38,300 --> 00:17:41,050 Some of the old riverbeds are still visible. 249 00:17:41,100 --> 00:17:44,350 But they pose more questions than the answer. 250 00:17:45,800 --> 00:17:51,250 Richard Young Professor of geology at the State University of New York at Geneseo 251 00:17:51,300 --> 00:17:56,250 has been trying to solve the riddle of the old river beds since he was a grad student. 252 00:17:56,500 --> 00:17:59,050 Young pieces together the history of rivers 253 00:17:59,100 --> 00:18:03,450 by looking at the shape and composition of rocks found on river beds. 254 00:18:04,200 --> 00:18:08,250 The modern Colorado River flows from the Rocky Mountains in the East 255 00:18:08,300 --> 00:18:11,950 to the Gulf of California in the Southwest. 256 00:18:12,000 --> 00:18:14,750 But as Young investigated the ancient canyons 257 00:18:14,800 --> 00:18:17,550 he found that something just didn't add up. 258 00:18:18,000 --> 00:18:20,650 It was a shock for a student who just is getting started 259 00:18:20,700 --> 00:18:23,350 and you want to believe what your professors are telling you, 260 00:18:23,400 --> 00:18:27,850 but everything you see out in the field says that something very different is happening. 261 00:18:31,900 --> 00:18:34,650 To us, these look like big pebbles. 262 00:18:34,700 --> 00:18:37,550 To geologists they're a missing link. 263 00:18:37,900 --> 00:18:40,450 We see two things, we see how round they are, 264 00:18:40,500 --> 00:18:42,250 which indicates how far they have come 265 00:18:42,300 --> 00:18:45,650 and secondly the rock types are completely foreign to this area 266 00:18:45,700 --> 00:18:48,550 and they come from at least a hundred miles away from here. 267 00:18:49,000 --> 00:18:53,550 The old stream pebbles are not native to the region where Young found them. 268 00:18:54,100 --> 00:18:58,450 They came from around 100 miles southwest of the plateau. 269 00:18:59,500 --> 00:19:02,050 The old river must have transported the pebbles 270 00:19:02,100 --> 00:19:06,550 from central Arizona north and west to the Plateau region. 271 00:19:06,900 --> 00:19:09,650 The orientation of the pebbles in the river bed 272 00:19:09,700 --> 00:19:12,450 shows the direction of the water flow. 273 00:19:12,700 --> 00:19:16,350 Rivers cause pebbles to tumble in the river channels. 274 00:19:16,400 --> 00:19:20,450 They move until they reach this position with the current flowing this way. 275 00:19:20,600 --> 00:19:23,350 That's a stable position, just like the shingles on a roof. 276 00:19:23,400 --> 00:19:26,650 And that tells us that the river was flowing in that direction. 277 00:19:27,000 --> 00:19:30,150 As the ancient pebbles settled on top of each other- 278 00:19:30,400 --> 00:19:33,850 they left a lasting record of how the river flowed. 279 00:19:34,800 --> 00:19:38,650 This was strong evidence that the rivers had to have flowed northeast- 280 00:19:38,700 --> 00:19:41,350 the opposite direction to today. 281 00:19:42,600 --> 00:19:45,950 But not only did the water flow in the opposite direction, 282 00:19:46,000 --> 00:19:51,150 it also in a different canyon 4 miles south of western Grand Canyon. 283 00:19:52,800 --> 00:19:55,350 The old channel is now empty. 284 00:19:55,700 --> 00:19:57,450 What happened? 285 00:19:59,600 --> 00:20:01,550 Deep within the earth's core, 286 00:20:01,600 --> 00:20:04,650 powerful forces were about to shatter the surface 287 00:20:04,700 --> 00:20:07,750 of what will become the Grand Canyon. 288 00:20:10,800 --> 00:20:12,850 About 20 million years ago 289 00:20:12,900 --> 00:20:17,750 the Oceanic Plate began moving north relative to the North American Plate. 290 00:20:24,200 --> 00:20:28,650 Heat built up under the Mogollan Highlands south west of the Canyon. 291 00:20:34,500 --> 00:20:38,050 The earth's crust began stretching. 292 00:20:40,500 --> 00:20:45,450 Over millions of years, vast areas of land deformed and cracked, 293 00:20:45,500 --> 00:20:48,650 sheared upward or snapped down. 294 00:20:49,100 --> 00:20:52,250 The Mogollan Highlands fell thousands of feet. 295 00:20:52,300 --> 00:20:55,450 Huge basins appeared on low-lying land. 296 00:20:55,500 --> 00:20:59,850 Today geologists call it the Basin and Range Province. 297 00:21:00,000 --> 00:21:03,150 Wayne Ranney uses dominoes to explain. 298 00:21:03,300 --> 00:21:08,150 Once faulting begins we tilt all the fault blocks down on individual faults 299 00:21:08,200 --> 00:21:12,350 and you can see the surface tilting back in the Colorado Plateau edge. 300 00:21:15,200 --> 00:21:19,650 Rock layers that were once horizontal are now almost vertical. 301 00:21:19,700 --> 00:21:22,150 The region tilted- and then collapsed. 302 00:21:22,200 --> 00:21:26,750 Ancient history is written in the orientation of every outcrop. 303 00:21:27,500 --> 00:21:30,550 The collapse re-drew the topography of the region. 304 00:21:31,100 --> 00:21:33,650 Before, the highlands to the south 305 00:21:33,700 --> 00:21:37,350 towered several thousand feet over the Colorado Plateau. 306 00:21:38,300 --> 00:21:39,450 After the collapse 307 00:21:39,500 --> 00:21:43,350 the Basin and Range area was almost half a mile lower. 308 00:21:43,800 --> 00:21:46,850 It was a major piece in the scientific puzzle. 309 00:21:47,000 --> 00:21:51,950 The rivers may have changed direction because the whole landscape changed 310 00:21:52,500 --> 00:21:56,350 When the basin and Range faulting occurred it dropped that area, 311 00:21:56,400 --> 00:21:59,250 it made it actually lower than the Colorado Plateau. 312 00:21:59,300 --> 00:22:02,450 And that's the reason that the rivers were able to change direction 313 00:22:02,500 --> 00:22:05,350 and flow in the opposite direction towards California. 314 00:22:06,900 --> 00:22:11,050 Scientists think they have solved the mystery of how the rivers reversed 315 00:22:11,300 --> 00:22:15,350 But the river was still four miles away from where the canyon is today. 316 00:22:15,600 --> 00:22:18,650 These ancient rivers did carve canyons- 317 00:22:18,700 --> 00:22:22,850 but not where today's canyon is, and on nothing like the same scale. 318 00:22:23,600 --> 00:22:26,850 Sometime after the collapse a new river formed- 319 00:22:26,900 --> 00:22:28,550 the Colorado River- 320 00:22:28,600 --> 00:22:30,350 and it took a new course. 321 00:22:30,400 --> 00:22:32,950 But when- and why? 322 00:22:33,600 --> 00:22:37,650 The challenge was to find the earliest sign of this river. 323 00:22:37,900 --> 00:22:42,450 Surprisingly, a clue came from outside the Grand Canyon. 324 00:22:42,700 --> 00:22:44,650 In the Lower Colorado river 325 00:22:44,700 --> 00:22:48,850 about 100 miles before the river enters the Gulf of California 326 00:22:49,000 --> 00:22:52,150 scientists discovered a tiny fossil. 327 00:22:54,000 --> 00:22:58,250 Kristin McDougall, research geologist with the US Geological Survey 328 00:22:58,300 --> 00:23:00,250 has studied these fossils. 329 00:23:00,300 --> 00:23:02,550 They are called Foraminifers. 330 00:23:02,600 --> 00:23:06,150 Foraminifers are like specks of dust. 331 00:23:06,200 --> 00:23:08,450 It's a microscopic seashell. 332 00:23:08,500 --> 00:23:14,150 The Cretaceous planktic foraminifers that we find 333 00:23:14,200 --> 00:23:17,750 look like three golf balls hooked together. 334 00:23:18,600 --> 00:23:20,350 Foraminifers are tiny- 335 00:23:20,400 --> 00:23:23,150 a hundred of them could fit on a grain of salt- 336 00:23:23,200 --> 00:23:27,150 but they could show when the river began cutting the canyon. 337 00:23:28,300 --> 00:23:31,950 The Foraminifers are not native in the Lower Colorado River. 338 00:23:32,000 --> 00:23:34,650 Their home was much further north. 339 00:23:34,800 --> 00:23:40,450 The only way their fossil remains could have been deposited in sediments in the lower Colorado River 340 00:23:40,600 --> 00:23:43,650 is when the river transported them down 341 00:23:43,900 --> 00:23:49,150 They were originally deposited in the Cretaceous shales 342 00:23:49,200 --> 00:23:52,850 on the Colorado Plateau north of the Grand Canyon. 343 00:23:53,000 --> 00:23:55,250 And they were eroded 344 00:23:55,300 --> 00:23:59,550 and brought down along the modern course of the Colorado River 345 00:23:59,600 --> 00:24:01,450 and re-deposited. 346 00:24:05,300 --> 00:24:10,850 Dating the sediments where the fossils were re-deposited helps to solve the mystery. 347 00:24:11,200 --> 00:24:15,550 The sediments seem to have formed when the river took its present course- 348 00:24:15,600 --> 00:24:17,150 and geologically speaking, 349 00:24:17,200 --> 00:24:19,850 it happened just an eye-blink ago. 350 00:24:19,900 --> 00:24:27,150 These Cretaceous fossils indicate that the Colorado River became a through-flowing river 351 00:24:27,200 --> 00:24:30,050 by at least four and a half million years ago. 352 00:24:30,300 --> 00:24:33,150 That's a very exciting find. 353 00:24:33,200 --> 00:24:36,650 Evidence indicates that 4.5 million years ago 354 00:24:36,700 --> 00:24:41,650 the river flowed along its present course from the northeast to the southwest. 355 00:24:41,800 --> 00:24:45,750 Scientists think they solved the mystery of the age of the river. 356 00:24:45,800 --> 00:24:48,750 But the solution raised a new question. 357 00:24:48,800 --> 00:24:51,050 They knew when the river had formed 358 00:24:51,100 --> 00:24:53,550 but they were still not certain how. 359 00:24:56,500 --> 00:24:59,650 Most rivers begin energetically at their source. 360 00:24:59,700 --> 00:25:01,950 They rip through the terrain downwards 361 00:25:02,000 --> 00:25:04,150 eroding anything in their path. 362 00:25:05,000 --> 00:25:07,750 Downstream, things seem calmer. 363 00:25:08,300 --> 00:25:11,450 The water moves slower, and the channel is wider. 364 00:25:13,200 --> 00:25:14,950 But back near the source, 365 00:25:15,000 --> 00:25:20,450 the river lengthens its channel upstream as the rushing waters erode more rock. 366 00:25:21,500 --> 00:25:23,750 They cut their channel headward. 367 00:25:24,000 --> 00:25:28,650 One theory is that the Colorado River got started this way. 368 00:25:28,800 --> 00:25:34,050 This headward erosion usually happens where the steepness of a riverbed rises. 369 00:25:34,100 --> 00:25:38,050 It gives the river more energy to cut deeper into the rocks. 370 00:25:38,100 --> 00:25:42,050 The steeper the gradient the more rainwater channels into the river 371 00:25:42,100 --> 00:25:44,850 and the faster it pulls down the slope 372 00:25:45,700 --> 00:25:48,350 The river eats into soil and rock at the top 373 00:25:48,400 --> 00:25:51,250 and may also lengthens its channel headward. 374 00:25:53,100 --> 00:25:55,650 Could headward erosion have been the mechanism 375 00:25:55,700 --> 00:25:59,650 that made the Colorado River head out across the plateau? 376 00:26:00,000 --> 00:26:05,950 We know that the Colorado plateau rose about a mile above sea level 70 million years ago 377 00:26:06,000 --> 00:26:10,350 creating a steep slope towards the present-day Gulf of California. 378 00:26:11,300 --> 00:26:14,750 It's a neat explanation but it's controversial. 379 00:26:15,000 --> 00:26:19,850 The modern Colorado River is only around 4 1/2 million years old. 380 00:26:19,900 --> 00:26:24,550 And the plateau rose 65 and half million years earlier. 381 00:26:25,400 --> 00:26:27,650 Perhaps there was another more recent uplift 382 00:26:27,700 --> 00:26:30,750 that would explain how the river crossed the plateau. 383 00:26:31,000 --> 00:26:32,750 Searching for clues 384 00:26:32,800 --> 00:26:37,550 scientists discovered a layer of rocks downstream in the lower part of the region 385 00:26:37,600 --> 00:26:39,450 called the Bouse formation. 386 00:26:40,800 --> 00:26:43,850 These rocks are around six million years old, 387 00:26:43,900 --> 00:26:47,750 and some parts are nearly 2,000 feet above sea level. 388 00:26:48,000 --> 00:26:52,550 When scientists took a closer look and discovered marine fossils in the rock 389 00:26:52,600 --> 00:26:55,750 they knew they were onto something extraordinary. 390 00:26:58,000 --> 00:27:02,150 There are three key fossils that we find in the Bouse Formation, 391 00:27:02,200 --> 00:27:04,350 the first is a planktic foraminifer 392 00:27:04,400 --> 00:27:07,450 which is one of the ones that floats on the surface of the water 393 00:27:07,500 --> 00:27:10,850 and then there is a specimen called ammonia 394 00:27:10,900 --> 00:27:13,150 and it's a very shallow water foram. 395 00:27:13,200 --> 00:27:18,150 And then there's a third kind that lives much deeper in the ocean. 396 00:27:18,800 --> 00:27:23,250 The fossils meant the rock layer is likely to have formed in seawater. 397 00:27:24,000 --> 00:27:25,950 For Dr. Ivo Lucchitta, 398 00:27:26,000 --> 00:27:29,150 the fossils led to a new theory of what had happened here. 399 00:27:30,500 --> 00:27:33,850 He believes that when the Gulf of California first opened up, 400 00:27:33,900 --> 00:27:38,350 it extended about 100 miles further north than it does today. 401 00:27:39,000 --> 00:27:42,050 Dead marine organisms sank to the sea bed 402 00:27:42,100 --> 00:27:45,550 and became entombed in the white sedimentary deposit- 403 00:27:45,600 --> 00:27:46,950 the Bouse Formation. 404 00:27:47,500 --> 00:27:51,150 Yet today, the fossils are hundreds of feet above sea level. 405 00:27:51,400 --> 00:27:54,150 That was the clue that he had been searching for. 406 00:27:54,300 --> 00:27:59,450 One day by looking at the present distribution elevation of remnants of the Bouse 407 00:27:59,500 --> 00:28:02,050 it occurred to me that the Bouse and the land with it 408 00:28:02,100 --> 00:28:06,750 had been uplifted as much as perhaps 1700 feet in the last 5 million years. 409 00:28:10,200 --> 00:28:14,250 He believes that this area was uplifted to its current elevation 410 00:28:14,300 --> 00:28:18,550 after the fossils were deposited around 6 million years ago. 411 00:28:18,800 --> 00:28:23,850 And this second uplift created an ideal scenario for headward erosion. 412 00:28:23,900 --> 00:28:25,850 By uplifting the plateau 413 00:28:25,900 --> 00:28:31,750 you basically steepen the gradient of the river as it emptied into the Gulf 414 00:28:31,800 --> 00:28:34,550 and therefore allowed them to erode more rapidly. 415 00:28:35,500 --> 00:28:38,350 The trouble is, not everyone agrees. 416 00:28:38,400 --> 00:28:41,950 The apparent existence of marine fossils in the Bouse Formation 417 00:28:42,000 --> 00:28:44,050 1000 feet above sea level 418 00:28:44,100 --> 00:28:48,150 is not irrefutable evidence that the area was uplifted. 419 00:28:48,400 --> 00:28:52,650 Senior geologist John Spencer from the Arizona Geological Survey 420 00:28:52,700 --> 00:28:55,650 is not convinced about the second uplift theory. 421 00:28:56,000 --> 00:29:00,350 I just was uneasy with the idea that the Earth would just go up and down like that, 422 00:29:00,400 --> 00:29:02,250 I call it trampoline tectonics. 423 00:29:02,400 --> 00:29:04,850 I didn't believe in trampoline tectonics 424 00:29:07,300 --> 00:29:11,350 Spencer and his team examine the Bouse rocks in the lab. 425 00:29:11,400 --> 00:29:15,550 They are especially interested in the levels of strontium isotopes. 426 00:29:16,400 --> 00:29:18,650 Strontium isotopes found in these rocks 427 00:29:18,700 --> 00:29:22,850 are irregular atoms undetectable to conventional microscopes. 428 00:29:23,000 --> 00:29:25,750 They come in heavier and lighter forms. 429 00:29:27,000 --> 00:29:31,150 The relative concentration of heavy and light forms varies. 430 00:29:31,200 --> 00:29:33,650 It depends on the origin of the water. 431 00:29:34,000 --> 00:29:39,850 River water usually has a different strontium isotope concentration than ocean water. 432 00:29:41,700 --> 00:29:43,550 Depending on the concentration 433 00:29:43,600 --> 00:29:45,550 scientists can often determine, 434 00:29:45,600 --> 00:29:49,450 if sediment was formed in freshwater or in the sea. 435 00:29:52,300 --> 00:29:58,550 Spencer's graph of the isotope concentration of the Bouse formation confirms his suspicions. 436 00:29:59,500 --> 00:30:03,350 The green dots represent isotopic concentrations of sea water, 437 00:30:03,400 --> 00:30:07,250 the blue dots represent ratios typical for river water. 438 00:30:07,300 --> 00:30:10,450 The red dots are his readings from the Bouse formation. 439 00:30:10,500 --> 00:30:12,550 They indicate freshwater. 440 00:30:13,600 --> 00:30:17,450 When we got our first results it was immediately clear that 441 00:30:17,500 --> 00:30:22,950 we were seeing no marine signature in any of the Bouse samples. 442 00:30:23,000 --> 00:30:24,550 We were a little surprised. 443 00:30:24,600 --> 00:30:29,250 We didn't expect that every number would come out looking like river water. 444 00:30:30,700 --> 00:30:36,350 These results question the validity of the second, more recent uplift theory. 445 00:30:37,400 --> 00:30:40,550 If the Bouse Formation was never under the sea, 446 00:30:40,600 --> 00:30:43,050 the uplift theory couldn't apply- 447 00:30:43,200 --> 00:30:47,850 and headward erosion along the lower Colorado could not have happened. 448 00:30:48,800 --> 00:30:51,050 Scientists had to look for another model 449 00:30:51,100 --> 00:30:53,950 explaining how the river cut across the plateau. 450 00:30:54,800 --> 00:30:58,450 About 250 miles west of Grand Canyon village 451 00:30:58,500 --> 00:31:02,350 there is a canyon system called the Lake Manix Basin. 452 00:31:03,100 --> 00:31:07,250 Norman Meek Professor of Geography at Cal State San Bernardino 453 00:31:07,300 --> 00:31:11,950 believes this area may offer a clue of how its bigger cousin got started. 454 00:31:12,800 --> 00:31:17,350 The Lake Manix Basin has sometimes been called the Grand Canyon of the Mojave River, 455 00:31:17,400 --> 00:31:21,250 because of the spectacular landscape that's portrayed here, 456 00:31:21,300 --> 00:31:23,650 a miniature version of the Grand Canyon. 457 00:31:24,000 --> 00:31:29,850 The site of Lake Manix Basin is connected to Silver Soda Lake via a canyon. 458 00:31:30,000 --> 00:31:33,050 Meek wondered if the formation of this canyon 459 00:31:33,100 --> 00:31:36,250 could throw light on the formation of the Grand Canyon. 460 00:31:36,400 --> 00:31:39,450 First he examined the site of Lake Manix. 461 00:31:39,500 --> 00:31:42,050 Lake Manix is an extinct desert lake. 462 00:31:42,100 --> 00:31:46,250 It used to stretch over an area of more than 90 square miles. 463 00:31:46,300 --> 00:31:49,950 Yet, many thousands of years ago the lake disappeared. 464 00:31:50,900 --> 00:31:54,650 Meek wanted to find out when and why the lake drained. 465 00:31:55,000 --> 00:31:56,750 At the edge of lake Manix 466 00:31:56,800 --> 00:32:00,350 he found sediments of ancient shorelines from the old lake 467 00:32:01,200 --> 00:32:04,650 In the deposits he found freshwater shells. 468 00:32:05,500 --> 00:32:09,550 He took them to a radiocarbon dating lab to find out their age. 469 00:32:10,400 --> 00:32:14,450 Radio Carbon is an isotope that occurs in all living creatures. 470 00:32:15,400 --> 00:32:18,850 Its half life is almost 6000 years, 471 00:32:18,900 --> 00:32:24,450 which means after around 6000 years half of the original amount is gone. 472 00:32:26,900 --> 00:32:30,350 By measuring how much radio carbon is left in the shells 473 00:32:30,400 --> 00:32:33,050 scientists can determine their age. 474 00:32:33,200 --> 00:32:35,950 Meek found that the shellfish in the Manix basin 475 00:32:36,000 --> 00:32:38,650 were alive 19,000 years ago. 476 00:32:38,700 --> 00:32:40,950 But after that they died. 477 00:32:41,000 --> 00:32:43,650 At that point Lake Manix emptied. 478 00:32:44,000 --> 00:32:46,250 When he looked at Silver Soda Lake 479 00:32:46,300 --> 00:32:50,650 he found that it existed from around the time when Lake Manix emptied. 480 00:32:50,700 --> 00:32:53,650 Could these two lakes be connected? 481 00:32:55,300 --> 00:33:00,250 Meek suggested the canyon here was cut by a mechanism called spill over 482 00:33:00,900 --> 00:33:03,750 He theorized that 19,000 years ago 483 00:33:03,800 --> 00:33:07,250 heavy rainfall or snowmelts filled up the lake 484 00:33:07,300 --> 00:33:10,250 until finally the water spilled over the rim. 485 00:33:10,800 --> 00:33:13,150 The lake drained dramatically. 486 00:33:13,200 --> 00:33:14,950 Over a few thousand years 487 00:33:15,000 --> 00:33:17,850 it cut down through the rocks carved a canyon 488 00:33:17,900 --> 00:33:20,350 and then created Silver Soda Lake. 489 00:33:20,500 --> 00:33:22,950 It's just like a reservoir breaking, 490 00:33:23,000 --> 00:33:24,350 there is a lot of energy, 491 00:33:24,400 --> 00:33:30,150 that energy rips away the sediments and the bedrock that make up the canyon 492 00:33:30,200 --> 00:33:32,450 and you get a through-flowing river 493 00:33:33,200 --> 00:33:34,850 Scientists speculated 494 00:33:34,900 --> 00:33:38,950 that if spill over explained how a canyon formed in the Mojave desert, 495 00:33:39,000 --> 00:33:45,350 it could also explain how the Grand Canyon formed just 250 miles to the east. 496 00:33:45,400 --> 00:33:49,050 Now they just had to find the lake. 497 00:33:49,300 --> 00:33:51,350 Today there is no lake- 498 00:33:51,400 --> 00:33:54,950 but there are 200 feet of green layered deposits- 499 00:33:55,000 --> 00:33:58,450 remnants of an ancient lake called Lake Bidahochi. 500 00:33:58,500 --> 00:34:02,050 And so this green layer right here reflects the idea 501 00:34:02,100 --> 00:34:07,550 that Lake Bidahochi was in existence east of the Grand Canyon between 16 and 6 million years ago. 502 00:34:08,400 --> 00:34:09,950 Over 10 million years 503 00:34:10,000 --> 00:34:17,650 a lake deposited fine-grained sediments like silt, clay and sand mixed with grey volcanic ash. 504 00:34:18,400 --> 00:34:21,150 The deposits indicate the existence of a lake- 505 00:34:21,200 --> 00:34:25,150 but they don't show how the lake overspilled and carved the Canyon. 506 00:34:26,300 --> 00:34:31,150 Jon Douglass, Geography professor at Paradise Valley Community College in Arizona, 507 00:34:31,200 --> 00:34:33,850 wanted an effective way to test the theory 508 00:34:33,900 --> 00:34:36,250 He built a small scale model of the Grand Canyon 509 00:34:36,300 --> 00:34:38,950 to demonstrate how the lake could have overflowed. 510 00:34:40,300 --> 00:34:43,250 6 million years ago, the canyon wasn't yet carved- 511 00:34:43,300 --> 00:34:46,550 but Lake Bidahochi was full to the point of overflow. 512 00:34:47,400 --> 00:34:50,650 And then as the lake came in, the lake filled. 513 00:34:50,800 --> 00:34:51,850 It filled and filled, 514 00:34:52,000 --> 00:34:55,550 higher and higher and higher until it eventually spilled across the lowest point; 515 00:34:56,100 --> 00:34:58,150 across the Kaibab plateau. 516 00:34:58,300 --> 00:35:00,650 And then water poured down the other side; 517 00:35:00,700 --> 00:35:02,550 those waterfalls continued to retreat back 518 00:35:02,600 --> 00:35:05,450 and the whole time you're cutting Great Canyon. 519 00:35:07,000 --> 00:35:11,750 Douglass suggests that Lake Bidahochi drained and formed a stream. 520 00:35:12,600 --> 00:35:17,150 The steep gradient of the riverbed caused the stream to cut deep into the rock. 521 00:35:18,500 --> 00:35:21,650 Over time the size of the stream increased 522 00:35:21,700 --> 00:35:24,350 and more and more water poured out of the lake 523 00:35:24,400 --> 00:35:27,950 which in turn cut deeper and deeper into the rock. 524 00:35:29,900 --> 00:35:32,450 But not all geologists agree. 525 00:35:33,000 --> 00:35:38,350 They say there is no evidence of there ever being a lake large enough to carve the Grand Canyon. 526 00:35:38,600 --> 00:35:42,050 So at present there is still no definitive answer 527 00:35:42,100 --> 00:35:44,650 as to how the river came into existence 528 00:35:46,700 --> 00:35:48,150 What we do know 529 00:35:48,200 --> 00:35:52,250 is that when it began flowing around 4.5 million years ago, 530 00:35:52,300 --> 00:35:55,650 it cut a one mile deep scar in the surface. 531 00:35:56,500 --> 00:36:00,250 To cut that whole canyon in 5 million years is a considerable feat 532 00:36:01,500 --> 00:36:04,950 How did the Colorado river manage to cut the canyon. 533 00:36:05,700 --> 00:36:08,250 There are bigger rivers in the United States, 534 00:36:08,300 --> 00:36:10,150 which haven't cut deep. 535 00:36:11,000 --> 00:36:14,150 The biggest and longest river in North America 536 00:36:14,200 --> 00:36:17,450 is not the Colorado river but the Mississippi. 537 00:36:18,500 --> 00:36:22,950 It flows nearly 2500 miles from its source in Minnesota 538 00:36:23,000 --> 00:36:25,350 to its mouth at the Gulf of Mexico. 539 00:36:25,700 --> 00:36:29,450 It carries 10 times more water than the Colorado. 540 00:36:30,100 --> 00:36:33,850 Yet, the Mississippi did not carve a Grand Canyon. 541 00:36:35,600 --> 00:36:39,650 Evidently, volume of water is not the only factor. 542 00:36:41,100 --> 00:36:45,650 Something else gave the Colorado River its enormous cutting power. 543 00:36:48,200 --> 00:36:51,350 The Colorado River begins in the Rocky Mountains- 544 00:36:51,400 --> 00:36:53,450 9000 feet above sea level. 545 00:36:53,900 --> 00:36:58,950 On its course it drops ten feet for every mile it flows. 546 00:36:59,300 --> 00:37:03,350 The Mississippi on the other hand begins its journey in Minnesota- 547 00:37:03,400 --> 00:37:06,550 almost 1500 feet above sea level 548 00:37:06,600 --> 00:37:08,850 dropping less than a foot per mile. 549 00:37:11,900 --> 00:37:14,850 Although the Mississippi has 10 times more water 550 00:37:15,000 --> 00:37:17,350 it is a less erosive river, 551 00:37:17,400 --> 00:37:19,950 because it has a lower gradient. 552 00:37:20,800 --> 00:37:23,150 All rivers want to run downhill 553 00:37:23,200 --> 00:37:25,350 It is the golden rule of gravity. 554 00:37:25,600 --> 00:37:28,750 Two rivers can have the same amount of water, 555 00:37:28,800 --> 00:37:31,850 but for every one degree of extra gradient, 556 00:37:31,900 --> 00:37:35,750 the steeper river gets a one percent increase in power. 557 00:37:37,700 --> 00:37:42,750 My observations have been that this river and even some of its little tributary streams 558 00:37:42,800 --> 00:37:48,150 have enough power that they cut though any kind of rock like butter. 559 00:37:49,000 --> 00:37:53,750 The speed and depth of cutting also depends on the rock it is carving into. 560 00:37:55,200 --> 00:37:58,050 Hard rock like granite is much tougher 561 00:37:58,100 --> 00:38:00,550 so the river cuts a narrow gorge. 562 00:38:01,700 --> 00:38:06,050 Soft rock like shale is easy for water to cut through- 563 00:38:06,100 --> 00:38:08,550 so the river carves a broad canyon. 564 00:38:09,800 --> 00:38:13,450 With soft rock, as the sides erode away 565 00:38:13,500 --> 00:38:15,450 the canyon widens. 566 00:38:16,600 --> 00:38:21,150 Joel Pederson geomorphologist at Utah State University 567 00:38:21,300 --> 00:38:26,450 is on a quest to discover how the river cut away the canyon walls 568 00:38:27,500 --> 00:38:29,850 The information that we collect from this what we are doing, 569 00:38:29,900 --> 00:38:31,650 we're relating it to the history of the river 570 00:38:31,700 --> 00:38:34,650 and so what the river is doing in the past, 571 00:38:34,700 --> 00:38:39,450 as it's eroding it is also stopping sometimes and depositing sediment. 572 00:38:40,100 --> 00:38:44,350 Pederson is interested in finding out how fast the canyon erodes. 573 00:38:44,400 --> 00:38:47,850 He uses a technique called luminescence dating. 574 00:38:49,200 --> 00:38:52,550 This uses light to measure the age of a rock. 575 00:38:52,600 --> 00:38:57,250 It works on sediments containing minerals such as quartz or feldspar 576 00:38:57,300 --> 00:38:59,250 that have been buried in the dark. 577 00:38:59,300 --> 00:39:03,950 As sediment builds up it is gradually sealed away from the sun 578 00:39:04,300 --> 00:39:09,950 Pederson measures the amount of luminescence a sample gives off when exposed to light. 579 00:39:10,700 --> 00:39:13,050 This method can date sediments 580 00:39:13,100 --> 00:39:17,150 between a few hundred to several hundred thousand years old. 581 00:39:17,200 --> 00:39:20,050 We're collecting sediment that hasn't yet seen light, 582 00:39:20,100 --> 00:39:22,350 and the metal tube prevents it from seeing light. 583 00:39:22,400 --> 00:39:25,450 And we pull the tube out and take it back to the laboratory. 584 00:39:27,600 --> 00:39:28,950 In the laboratory 585 00:39:29,000 --> 00:39:32,250 scientists expose the samples of ancient river sediments 586 00:39:32,300 --> 00:39:34,650 to specific wavelengths of light. 587 00:39:35,500 --> 00:39:38,750 This energy excites the electrons in the sediment- 588 00:39:38,800 --> 00:39:43,050 some respond by releasing their own energy, in the form of light- 589 00:39:43,100 --> 00:39:45,550 and this minute signal is measured. 590 00:39:45,900 --> 00:39:50,250 The greater the response from the particles the longer they spent buried 591 00:39:52,300 --> 00:39:56,050 So it's telling us that moment in time, how many years ago it was, 592 00:39:56,100 --> 00:39:58,550 that the river actually deposited that sediment 593 00:39:58,600 --> 00:40:02,350 and then buried it under more sediment so it couldn't see light any more. 594 00:40:06,600 --> 00:40:10,850 When Pederson measured the incision rates along the whole length of the river 595 00:40:10,900 --> 00:40:13,250 he found something unexpected. 596 00:40:14,700 --> 00:40:20,350 179 miles downstream the canyon appeared less deep. 597 00:40:20,800 --> 00:40:24,250 Something changed and lessened the river's cutting power. 598 00:40:24,300 --> 00:40:29,650 Could it be that the river lost its power due to changes beneath the land itself? 599 00:40:29,900 --> 00:40:34,550 It was an intriguing puzzle scientists were desperate to solve. 600 00:40:36,700 --> 00:40:38,850 3 and a half million years ago 601 00:40:38,900 --> 00:40:44,150 the Colorado plateau ruptured and created a deep chasm across the canyon 602 00:40:44,200 --> 00:40:46,750 It's called the Toroweap fault. 603 00:40:47,600 --> 00:40:53,350 Tectonic activity along the fault slowly lowered the land of the plateau to the west. 604 00:40:53,600 --> 00:40:55,450 And as the land fell away, 605 00:40:55,500 --> 00:40:58,950 it weakened the cutting power of the river flowing over it. 606 00:40:59,800 --> 00:41:03,050 Karl Karlstrom explains with a loaf of bread. 607 00:41:03,100 --> 00:41:07,150 We'll imagine this loaf of bread as a stack of rocks 608 00:41:07,200 --> 00:41:11,450 that is going to be incised by the river to be the Grand Canyon. 609 00:41:11,500 --> 00:41:16,350 And we'll imagine this knife as the Colorado River itself, 610 00:41:16,400 --> 00:41:21,850 which over time can erode through even the hardest rocks to form a canyon. 611 00:41:21,900 --> 00:41:25,750 But many times there's a break in the crust called fault. 612 00:41:25,800 --> 00:41:29,550 And so if I incise the river at the same time 613 00:41:29,600 --> 00:41:32,550 that I am moving one block down, 614 00:41:32,600 --> 00:41:35,950 and I think you can see this if I turn it up like this, 615 00:41:36,000 --> 00:41:38,950 and you can see that on one side the canyon is quite deep 616 00:41:39,000 --> 00:41:40,950 and on the other much less deep. 617 00:41:42,800 --> 00:41:44,950 Scientists had their answer. 618 00:41:45,000 --> 00:41:46,850 The river stayed the same 619 00:41:46,900 --> 00:41:50,750 but the land west of the Toroweap Fault sank lower 620 00:41:50,800 --> 00:41:54,250 and so escaped the full cutting force of the water. 621 00:41:55,500 --> 00:41:59,050 The Colorado river has cut a masterpiece of a canyon. 622 00:41:59,100 --> 00:42:01,650 But water doesn't only destroy rock- 623 00:42:01,700 --> 00:42:05,150 amazingly it can also create it. 624 00:42:05,900 --> 00:42:12,150 Scientists are intrigued by new rocks within the canyon that are still growing. 625 00:42:15,900 --> 00:42:19,350 The Colorado river has been a great destroyer. 626 00:42:20,200 --> 00:42:22,750 In the last 4.5 million years 627 00:42:22,800 --> 00:42:26,850 it has excavated over 800 cubic miles of rock. 628 00:42:28,000 --> 00:42:30,650 It created a gorge so big 629 00:42:30,900 --> 00:42:33,350 that all of the river water in the world 630 00:42:33,400 --> 00:42:36,450 would fill the canyon to just over a third. 631 00:42:37,100 --> 00:42:39,650 But the river can also create rocks. 632 00:42:39,700 --> 00:42:41,550 At certain points in the canyon 633 00:42:41,600 --> 00:42:45,650 scientists have discovered new rocks forming today. 634 00:42:48,600 --> 00:42:52,450 Laura Crossey, Professor at the University of New Mexico 635 00:42:52,500 --> 00:42:56,550 is an expert on these rocks... the youngest in the canyon. 636 00:42:56,600 --> 00:43:00,050 The big story of Grand Canyon is the carving of this beautiful place, 637 00:43:00,100 --> 00:43:05,150 there are other processes such as travertine that cause changes to occur 638 00:43:05,200 --> 00:43:08,150 and the younger rocks to form inside that very canyon. 639 00:43:09,700 --> 00:43:11,850 These travertines are special 640 00:43:11,900 --> 00:43:16,150 because they are created from water saturated in carbon dioxide 641 00:43:16,400 --> 00:43:20,250 and they are actually formed at the bottom of the canyon itself. 642 00:43:21,100 --> 00:43:24,850 The carbon dioxide comes from deep inside the earth. 643 00:43:25,500 --> 00:43:27,650 It leaks out to the surface. 644 00:43:29,900 --> 00:43:32,350 Here, it dissolves in water, 645 00:43:32,400 --> 00:43:37,450 acidifying it and giving it the power to dissolve limestone. 646 00:43:40,100 --> 00:43:42,650 The carbon dioxide escapes from the water, 647 00:43:42,700 --> 00:43:45,250 forming bubbles like fizzy soda. 648 00:43:46,000 --> 00:43:50,150 As the gas escapes, it leaves behind calcium carbonate, 649 00:43:50,300 --> 00:43:52,650 which coats objects in its path. 650 00:43:54,500 --> 00:43:58,150 In some places it forms stone waterfalls. 651 00:43:58,200 --> 00:44:02,250 In others it covers sticks and twigs. 652 00:44:02,300 --> 00:44:06,050 So these are just small examples of the coatings of travertine 653 00:44:06,100 --> 00:44:10,050 that form on every stick and twig and cobble that comes down the stream-bed 654 00:44:10,200 --> 00:44:12,550 It accumulates into vast piles of sediment 655 00:44:12,600 --> 00:44:16,550 which are instantly formed into rock, the youngest rocks in the Grand Canyon. 656 00:44:18,900 --> 00:44:23,450 Every drop in the river has in some ways shaped the landscape here. 657 00:44:24,300 --> 00:44:28,250 But water does far more than destroying rocks and building them. 658 00:44:28,300 --> 00:44:29,850 Without the river- 659 00:44:29,900 --> 00:44:33,850 the current plant and animal life would struggle to survive. 660 00:44:34,000 --> 00:44:38,350 And it was the river which attracted early settlers here. 661 00:44:38,400 --> 00:44:44,250 When the ancestors of the Hualapai arrived in the Grand Canyon about seven hundred years ago 662 00:44:44,300 --> 00:44:48,850 they celebrated the Colorado River as an important source for life. 663 00:44:48,900 --> 00:44:51,150 And it remains that today. 664 00:44:51,300 --> 00:44:54,850 The river's all source of life out here. 665 00:44:54,900 --> 00:45:00,950 The canyon to me personally is something that our ancestors, they fought hard to retain. 666 00:45:01,000 --> 00:45:03,450 Because they knew the importance of it. 667 00:45:04,100 --> 00:45:10,250 Our wish is to maintain it in its natural state or its beauty. 668 00:45:11,400 --> 00:45:14,150 Modern visitors of the canyon are mesmerized 669 00:45:14,200 --> 00:45:17,950 as the first Native Americans would have been several hundred years ago. 670 00:45:19,400 --> 00:45:22,750 It's one of the natural wonders of the world. 671 00:45:24,400 --> 00:45:29,350 A monument to the age-old, colossal forces that created it. 672 00:45:36,200 --> 00:45:39,750 1.7 billion years ago it began. 673 00:45:41,900 --> 00:45:45,050 Layers of flat-lying, stratified sediments 674 00:45:45,100 --> 00:45:47,350 build up high canyon walls. 675 00:45:47,800 --> 00:45:53,150 Uplift elevates the plateau and rivers cut deep into the rocks. 676 00:45:53,700 --> 00:45:56,350 And the climate today is arid. 677 00:45:56,400 --> 00:45:58,050 Nothing is lost. 678 00:45:58,100 --> 00:46:00,150 Everything is visible. 679 00:46:00,600 --> 00:46:04,150 It is difficult to find a canyon as impressive as this one: 680 00:46:04,800 --> 00:46:07,350 Possibly in South-eastern Tibet, 681 00:46:07,400 --> 00:46:10,950 home of the biggest, longest and deepest canyon. 682 00:46:11,700 --> 00:46:14,450 The Yarlung Tsangpo Great Canyon. 683 00:46:15,100 --> 00:46:19,550 The climate is different and the area is covered with dense vegetation. 684 00:46:20,400 --> 00:46:24,550 The Euphrates is a very large river running through arid Iraq, 685 00:46:24,600 --> 00:46:27,150 a climate not dissimilar to Arizona. 686 00:46:27,400 --> 00:46:31,150 But this area never uplifted and formed a canyon. 687 00:46:32,900 --> 00:46:37,950 The Grand Canyon might not be the biggest and longest canyon on earth 688 00:46:39,500 --> 00:46:43,350 But the powerful forces that created it and made it unique 689 00:46:43,400 --> 00:46:45,350 are still hard at work. 690 00:46:46,600 --> 00:46:49,850 Nobody can predict how much uplift there will be. 691 00:46:49,900 --> 00:46:52,050 But if the river stays on course 692 00:46:52,100 --> 00:46:55,250 then the future of the Grand Canyon looks good. 693 00:46:56,100 --> 00:47:00,550 And if you think this is grand- you ain't seen nothing, yet. 694 00:47:00,600 --> 00:47:03,150 Stick around for another million years or two 695 00:47:03,200 --> 00:47:08,550 and the canyon might be even deeper with walls just as sheer as they are today. 696 00:47:08,600 --> 00:47:12,850 The Grand Canyon is just getting grander. 697 00:47:14,100 --> 00:47:19,100 www.mvgroup.org 698 00:47:22,100 --> 00:47:26,100 Preuzeto sa www.titlovi.com 63501

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