1、 Earth, a 4.5billion year old planet, still evolving. As continents shift and clash, Volcanoes erupt, glaciers grow and recede. The earths crust is carved in numerous and fascinating ways. Leaving a trail of geological mysteries behind.In this episode, Loch Ness, in the highlands of Scotland， is exp
2、lored. It holds more water than any other lake in Britain, with a bedrock containing some of the oldest rocks on the planet. Set in a landscape that was once part of America. Loch Ness is a lake with an enduring myth the Loch Ness monster. A team of scientists investigate how Loch Ness was made. The
3、 clues they uncover, also provide a window into the formation of the earth itself.Deep, dark and full of mystery. This is Loch Ness in the highlands of Scotland. For a thousand years there have been claims that this vast lake hides a strange and terrible secret the fabled Loch Ness monster. A mythic
4、al beast, suggested by some as a descendant of the dinosaurs which once roamed this part of Scotland. Loch Ness would be the perfect hiding place for a prehistoric monster. At 23 miles long and a mile wide, this vast freshwater lake covers the same area as New Yorks Manhanttan island. And its more t
5、han 700 feet deep. But the monster is not the only mystery that surrounds Loch Ness. In the hills above the loch, there is a type of rock whose origin baffled scientists for years. Its sandstone. And its the start of the investigation into how Loch Ness was made. “Its know as the old red sandstone a
6、nd its given that name because its red and its a sandstone and its called old because its about 350 million years old. ”The old red sandstone runs down one side of Loch Ness. But the most astonishing fact about these rocks is not their age, but where they come from. “These rocks actually belong to m
7、y homeland of North America because these rocks originated on the North American continent and then have separated from North America. But in many ways this is almost a little bit of home for me here in Scotland”But how do geologists know that this old red sandstone comes from 3000 miles away on the
8、 other side of the Atlantic Ocean? “These rocks are identical in age and character to the rocks that actually form the Catskill Mountains and so this part of Scotland belonged to northeastern North America”.For more than a thousand years, old red sandstone has been used for building castles in this
9、part of Scotland. But its also been quarried in the US and used for brownstone building in New York City. Under the microscope rocks from both continents have an identical crystal structure and chemical analysis has also proved that theyre exactly the some age. But how did part of America end upon t
10、he shores of Loch Ness?To answer this crucial question the investigation mast go much further back in time to look for evidence in the ancient bedrocks of northern Scotland. Its here that the story of Loch Ness begins. The trail starts north of Loch Ness, where the bedrock comes to the surface; this
11、 landscape is full of the extraordinary mysteries of an unimaginably ancient past. Its made of a type of rock called Lewisian Gneiss. Recent drilling and blasting for a new road cut have exposed evidence which uncovers a amazing chapter in earths history. The long straight lines are the drill holes
12、left in the rock face. Modern radioisotope dating has given geologists the first clue to understanding the origin and formation of these rocks. “These rocks are very special to geologists. They are some of the very oldest rocks in the world. We see them in very few places perhaps a dozen places acro
13、ss the globe contain rocks of this age, talking about two and a half to three billion years old”.The origin of the gray Lewisian Gneiss lies in the first crust that cooled on the surface of the earth. After its formation 4.5 billion years ago, part of this crust were mixed together with the earliest
14、 sediments, buried, re-melted and forced back up again and again for more than a billion years. These extraordinary rocks are the result of that devastating period in our planets history. And theres more evidence exposed in this road cut revealing crucial information about the early history of the L
15、och Ness region. “This exposure contains three important pieces of geological jigsaw puzzle. First, we have the gray gneiss of 2.5 to three billion years old. Secondly, we have this black igneous material which has been intruded into the area. This is two billion years old. And thirdly, we have this
16、 pink granitic intrusion that both intrudes the black material and the gneiss and this is 1.8 billion years old”This evidence reveals that after the formation of the Lewisian Gneiss, much younger rocks were then melted and mixed into the ancient crust. But this process took an incredible length of t
17、ime.“What weve got here are rocks that record over a billion years of earth history. Now, to put that into perspective that is almost a quarter of the age of the earth recorded in this exposure”This is the bedrock of Loch Ness. It carries an extraordinary story of a major part of earths history. And
18、 there are yet more secrets hidden in these rocks.“It looks very much because of the temperatures and pressures that these rocks were under that theyve been to depths of perhaps 50 miles beneath the earths surface in the past. This suggests that these rocks have been to hell and back two or three oc
19、casions over a billion year period”Geologists now know that the only force powerful enough to produce this extraordinary mix of rocks is plate tectonics.Plate tectonics is the process by which the giant plates of the earths crust are driven slowly across the planets surface by vast convection curren
20、ts deep in the earths hot mantle. In the Loch Ness region, the evidence in the road cut reveals that incredible pressures forced the crust deep down into the earth where it was melted, deformed, mixed together, then finally brought back to the surface. After that, for another billion years, this anc
21、ient land mass quietly eroded down to a rough, rolling landscape. But this wasnt the green terrain we see now. There was much less oxygen in the earths atmosphere than today and the surface would have looked like a lunar landscape, desolate and sterile. Incredibly, remnants of that billion year old
22、landscape are still preserved today. The clues are revealed in another road cut, where the trained eye can draw amazing conclusions from what looks like a jumble of rocks.“At this road cut, we can see Lewisian Gneiss which is between two and a half and three billion years old. But up here we have so
23、mething completely different. If I go up to this level and look above it, we have horizontally bedded red sandstones” This sudden change in rock type helps to unravel the mystery hidden in these ancient formation. “Theyre believed to have been laid down in a continental environment by rivers. Weve g
24、ot river systems that laid down horizontally bedded sedimentary rocks on ancient landscape”So this simple outcrop reveals that even in a world with little oxygen, the ancient bedrock of Scotland was covered in rivers a billion years ago. And theres yet another secret hidden here.“There is a junction
25、 between these rocks which are almost a billion years old and the rocks below that are two and a half to there billion years old. This is a major time gap of between one and half and two billion years”The time gap revealed here is extraordinary. It shows that after the traumas of their early formati
26、on, the rocks of the Loch Ness region went through a period of calm which lasted more than a third of the age of the earth. The investigation into how Loch Ness was made has uncovered its first evidence. Identical old red sandstone found on two continents proves that Scotland and America were once j
27、oined together. Some of the oldest rocks in the world reveal that the bedrock underlying Loch Ness was made during the primeval creation of the earths crust. Bedded sandstones lying on the ancient bedrock slow that rivers flowed over this landscape a billion years ago, during a long period of tranqu
28、ility. But the calm couldnt last forever. A major continental collision was looming and with it the union between Scotland and England.The investigation into how Loch Ness was made will next uncover the geological structures which would eventually create Loch Ness. The search for evidence begins wit
29、h a 19th-century scientific mystery. In the 1880s, geoloists in Scotland were baffled by a sequence of rocks they found north of Loch Ness. Here in a remote hillside lay the problem. A huge mass of very old lewisian gneiss was lying on top of much younger rocks. But the 19th-century geologists had n
30、ever encountered this before. In their experience younger rocks always lay on top of older beds. Then, one scientist invented a novel approach to try to solve the puzzle. “A survey geologists back in the Victorian age, 125 years ago mapped this area and his name Henry Cadell. He went back to Edinbur
31、gh and he worried about what hed seen in the field and thought “how do I replicate what Ive seen? How does this happen?“ So he built a model, and he attempted then to show what it was that he saw in the field”Cavells model was simple. He suspected that some force had squeezed the rocks horizontally
32、to make this upside-down sequence, so he built an apparatus containing layers of sand and clay to test his idea, Professor Underhill is using a replica of Cadells equipment, filled with alternating layers of black sand and plaster of paris to try and duplicate Cadells experiment. Turning the screw w
33、inds the block forward, imitating the horizontal pushing force that Cadell thought was the culprit. As the horizontal force increases, the layers are pushed over each other along a shallow plane which geologists now call a thrust fault?“And weve got the first thrust appearing. Oh, look at that, anot
34、her thrust going in”The experiment showed Cadell exactly how older layers the ones on the bottom are pushed over and on top of the younger layers along the plane of the thrust fault. “Theres some beautiful structures in here, theres a thrust fault running through here which duplicates the white laye
35、r and another one through here and the final thrust fault which is at the lowest angle out here towards the left-hand side. A success in terms of a simple model replicating what we see on the ground, and i can see how Cadell and others, when attempting such things began to understand what it was tha
36、t they saw in the field. They could replicate it in a simple, crude model, but replicate it in a very successful manner”Once Cadell and his colleagues understood the principle of thrust faults, the apparently illogical sequence of the rocks, they saw in northwest Scotland began to make sense. “Well,
37、 the slope represents a thrust fault. What we have underneath it is a bedded younger quartzite succession which is pink. Above it, the gray rock, the rubbly gray hillside we see above is the Lewisian Gneiss again. And the surface in between which is puttingolder rock, the gray material onto the pink
38、 rock, the younger material is the thrust fault just like in the model that we saw before”Geologists now know that a thrust fault is the smoking gun that shows where continents have collided. But which continents were colliding to make the thrust faults in Scotland? And how were they involved in mak
39、ing Loch Ness? The scientists trail now led them to another thrust fault, the Moine thrust. The Moine Thrust is one of the biggest thrust faults on Earth. Running for 120 miles down the northwest of Scotland its mostly hidden from view but Professor Underhill has found one of the rare locations the
40、where the thrust can be seen on the surface. This apparently insignificant join between two rock layers is the actual line of the thrust and it reveals a geological bombshell. The dark layer above the thrust comes from England but the surprise lies in the yellow limestone below it. Just like the old
41、 red sandstone at Loch Ness this rock comes from North America. This one small piece of evidence has enormous implications for the formation of Loch Ness.“The amazing thing about this contact is that its the meeting point between two continents. So here we are on a wet Scottish hillside on a Sunday
42、afternoon and I am touching the contact between, effectively America and northwestern Scotland on one hang and England on the other as was 425 million years ago”But how did these two ancient continents collide?450 million years ago a supercontinent containing North America and Scotland lay deep in t
43、he southern hemisphere. At its margin was an ocean wider than the present-day Atlantic. On the other side was England and Europe. But the forces of plate tectonics were slowly pushing the two land masses together.“Well, around 450 million years ago there was a major ocean where were standing now. It
44、 was called the lapetus Ocean and it separated America and northwestern Scotland on one hand from southeastern Scotland and England on the other hand. Now, what happened in the 20 million years after that ocean closed and eventually was closed sufficiently that two continents collided into each othe
45、r”The collision between America and Europe pushed massive layers of rock over each other forcing upwards a range of mountains higher than the Himalayas are today. Still firmly attached to America, Scotland and England became fused together. But what did this collision have to do with the making of L
46、och Ness? The Loch itself provides the most fundamental evidence. “The one thing thats quite striking about Loch Ness is that when you look at it particularly from this perspective you can see that it runs straight, almost straight as an arrow and that straightness goes on for about 20 miles. And as
47、 a geologist that tells me that there has to be a control on this topographic straightness because nature doesnt produce things in straight lines. And so there is a structure here that is controlling the overall shape of Loch Ness itself” The structure is the Great Glen Fault a major geological faul
48、t line formed during the continental collision 425 million years ago. It runs for more than 300 miles right across Scotland slicing the country in two. Loch Ness exactly follows the line of the Great Glen Fault. “The Great Glen Fault is not a thrust fault like the Moine Thrust where material has bee
49、n pushed up over its not a normal fault where material drops down vertically its lateral motion”The Great Glen Fault is Scotlands version of the San Andreas Fault its just 400 million years older. The Great Glen Fault is no longer active but this giant split in the Earth a crust has been a feature of the Scottish landscape for more than 400 million years. Its the foundation of Loch Ness and without it the Loch could not exist. Nor could the legend of the Loch Ness monster. The investigation into how Loch Ness was made has uncovered mor
