WEBVTT 1 00:00:02.266 --> 00:00:06.865 The natural elements, in the sense of the actions of Earth’s air and water 2 00:00:06.866 --> 00:00:10.699 cause a continuous wearing down of rocks and soils. 3 00:00:10.700 --> 00:00:15.832 This is erosion which thus shapes the landscape in many different ways. 4 00:00:17.566 --> 00:00:22.199 Atmospheric agents can act to produce physical or chemical effects. 5 00:00:22.200 --> 00:00:25.399 The wind carries away fine particles of soil 6 00:00:25.400 --> 00:00:29.265 redepositing them, sometimes very far away. 7 00:00:33.566 --> 00:00:37.565 This is also how it creates the dunes in deserts and on coasts 8 00:00:37.566 --> 00:00:40.365 which it ceaselessly reshapes. 9 00:00:42.466 --> 00:00:44.499 Rain washes out soils 10 00:00:44.500 --> 00:00:49.365 but also dissolves limestone because of the Carbonic Acid it contains. 11 00:00:51.562 --> 00:00:55.975 Alternate thawing and freezing breaks down rocks. 12 00:01:00.066 --> 00:01:04.365 Flowing water, as in a river, slowly digs V shaped valleys 13 00:01:04.366 --> 00:01:09.399 above all when the current is rapid and the flow large. 14 00:01:09.400 --> 00:01:16.032 In grinding down the rocky base beneath them, glaciers create large U shaped valleys 15 00:01:16.033 --> 00:01:22.799 which one continues to observe long after the glaciers themselves have disappeared. 16 00:01:22.800 --> 00:01:27.065 Every year, billions of tons of sands, muds and rocks 17 00:01:27.066 --> 00:01:31.399 make up a large part of the sediments that are later transported elsewhere 18 00:01:31.400 --> 00:01:34.165 by air and water. 19 00:01:34.166 --> 00:01:37.065 They end up accumulating, under the force of gravity 20 00:01:37.066 --> 00:01:41.265 above all at the bottoms of seas, lakes and large rivers 21 00:01:41.266 --> 00:01:44.599 where they form thick sedimentary layers. 22 00:01:44.600 --> 00:01:49.265 With the passage of time and under certain conditions of pressure and temperature 23 00:01:49.266 --> 00:01:52.565 these sedimentary layers become greatly compacted 24 00:01:52.566 --> 00:01:59.599 to the point that they form the rocks called sedimentary, like limestones and sandstones. 25 00:01:59.600 --> 00:02:02.065 As a result of geological movements 26 00:02:02.066 --> 00:02:06.965 these rocks can find themselves back in the open air where they, in their turn 27 00:02:06.966 --> 00:02:09.966 are subjected to the erosive actions of the elements.