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It started long ago and continues today, with lots of fire and ice, mountain peaks and ocean waves, and more time than we can imagine. The story begins with Igneous rock, like this piece of granite. Igneous means fire. This granite was created in a fiery place, perhaps long long ago. Billions of years in the past, when earth was new, there were no rocks. Earth was a burning hot gooey ball of melted minerals and metals called magma. Eventually, as heat drifted into space, earth's surface cooled. A thing crust of rock formed over it like ice over a lake in winter. This crust made of minerals and metals, cooled from red hot magma, was igneous rock. Some of that original rock formed more than three billion years ago can still be found today. It is among earth's oldest objects. If it had ice, that rock would have seen the start of life, the making of Coal and Oil, the rise and fall of dinosaurs, and the world's first person. That rock would have seen it all. Igneous rock is not only one of our oldest rocks, it is also some of our newest. Earth has never stopped making it. Somewhere people probably watch it formed right now, at the edge of volcanoes. Lava is magma spewed out by a volcano. It hardens into igneous rock. Volcanoes also shows us that the inside of Earth is still full of fiery magma, not cooled into sold rock. Igneous rock occurs in many forms. They vary according to the minerals and metals they are made of, and how fast they're cooled. Granite cools slowly underground over thousands of years. Obsidian which looks like black glass cooled quickly, as did pumice, which floats in water. Though varied, all igneous rock hardened directly from magma. The second rock of our story is the Sedimentary rock. A sedimentary rock develops through a long process that starts with weathering and ends with lithification. Weathering breaks down rocks on Earth's surface through mechanical, chemical and biological forces. In mechanical weathering, heat, cold, ice, wind blown sand, and falls, slowly crack and wear down rocks. In chemical weathering, rock dissolves in rain water which is slightly acid. In biological weathering, plant-roots both crack and dissolve rocks. Weathering occurs slowly. But, old grave stones in cemeteries show what can happen to exposed rock. Over time, even huge mountains weather bit by bit, into sand, dust, clay and minerals dissolved in water, and disappear. 200 million years ago, the Appalachian mountains were several times their present height. Where did the mountains go? They get carried away through erosion. Wind and especially water, moves each bit of mountain rock downhill. Eventually, eroded rock fills up nearby valleys, or gets carried away in a river out to sea. We call the moved materials, sediments. Wherever they settle, sediments accumulate in layers. In oceans, sediment layers make row higher than our tallest mountains. Upper sediment layers press down on lower ones. This helps in lithification, the process that turns sediments into stone. Sometimes layers get squeezed so hard, sediment grains get shoved into one other and lock into place. Other times, water evaporates from a layer and leaves behind minerals that glue together to the tightly-packed grains. Either way, what was once sand, mud or gravel, becomes sedimentary rock. Depending on how it formed, sedimentary rock may be quite hard, or rather weak and crumbling. Sedimentary rock may not stay forever where it settled. Strong forces within earth sometimes push up rock from the bottom of the valley or an ocean into spectacular peaks and long mountain chains. Once sedimentary rock or any other kind of rock, gets uplifted, it undergoes another cycle of weathering. Those same strong forces that push rock up may instead push rock down. If the rock is pushed deep enough, it melts. Some future day, the melted minerals and metals may harden underground, or erupt from a volcano to form new igneous rock. This story's third chapter tells about Metamorphic rock. Metamorphic means changed. Metamorphic rock may start as igneous, sedimentary or even another metamorphic rock. But, somewhere deep underground, gets changed by heat and pressure. For example, limestone metamorphoses into marble, granite metamorphoses into gneiss. But, once reflexive black minerals, are now stripes or layers of it. The heat and pressure that metamorphose rock is not enough to melt it, but, still enough to cause changes. We might compare a metamorphic rock to a hard-boiled egg. This is still an egg, but, it has changed a great deal. Many people consider marble to be the most beautiful of all rock. However, even the beauty of metamorphic rock cannot protect it from the forces of weathering. If uncovered, it too, will eventually fall as sediments. So, these are three rocks, Igneous, Sedimentary and Metamorphic. Some are as old as can be, others are as new as today. In a way, they are all the same, because, they all started as hardened magma. But still, each is different, because, rocks can change. Infact, they make a rock cycle, in which they change forms, shapes and places. With each turn of the cycle, minerals and resources are remixed and unlocked. And, the earth, through this change, remains rich and fresh. Who would have thought these three rocks could tell such a remarkable story? Main types of rock. You might be surprised to learn that rocks can actually change from one type to another. The term Rock cycle refers to the processes through which rocks of one type are transformed slowly over long periods of time, into rocks of another type. The ranger reminds you that you've already seen a few examples of this. For instance, conglomerate sedimentary rocks can be made up of pieces of igneous or metamorphic rocks, or even other sedimentary rocks. And, igneous and sedimentary rocks, exposed to heat and pressure, can be transformed into metamorphic rocks. Now, let's study the rock cycle in detail. Igneous rocks can be broken down through weathering, and the pieces can form sedimentary rocks. Igneous rocks can also change into metamorphic rocks, when exposed to heat and pressure that change them, but, don't melt them completely. If exposed to high enough heat, they can melt back into magma to form new igneous rocks. Sedimentary rocks can break down through weathering to form new sedimentary rocks. They can also be transformed into metamorphic rocks through the action of heat and pressure. If the get hot enough, they can melt into magma to form igneous rocks. Metamorphic rocks can break down to form sedimentary rocks. They can also be converted into different metamorphic rocks when exposed to heat and pressure. Like igneous and sedimentary rocks, metamorphic rocks can melt into magma to form new igneous rocks. As you can see, the interaction between the three main rock types can take several different paths. And, any rock can turn into another type of rock, with the right condition.

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Duration: 10 minutes and 55 seconds
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Language: English
License: Dotsub - Standard License
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Views: 13
Posted by: pgtranscribes on Apr 4, 2015

13.Video-1

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