§ 18. Species that constitute the Earth crust
1. Think you know minerals and rocks.
2. What power has the crust under the continents and oceans?
Composition the crust.Crust consists of minerals and rocks, which exists in nature several thousand species. Minerals and rocks are different colors, hardness, structure, melting point, solubility in water and other properties. Many people commonly use, such as fuel, construction, for ferrous and nonferrous metals.
Diversity minerals and rocks is mainly due to different conditions formation. By origin they are divided into igneous, sedimentary and metamorphic.
Magmatic breed. Magmatic called species, which formed from magma. Magma (From Greek - "a thick ointment) - fiery liquid melt that formed in the mantle. In the Earth's crust or on the surface it gets through the deep cracks. Crack causes a release of pressure in the depths. The substance of the mantle is plastic and molten liquid and penetrates into the ground.
Rising, heated to 1000 0C magma slowly cools. At great depths it cools down hundreds and even thousands of years! In the earth's crust magma may zatverdnuty at depths as water during freezing. Then formed Deep magmatic rocks. These include, for example, granite. If the magma reaches the surface and pouring, then it gets rid of dissolved gases in it and turns on the bench. During solidification of lava formed eruptive magmatic rocks. Thus the common basalts on Earth. Igneous rocks (gabbro, labradorite, feldspars, etc.). Mostly solid, heavy and dense.
Sedimentary breed.In contrast, magmatic, sedimentary rocks formed on the surface of the crust. They arise as a result of settling matters on a day of water or accumulation of land. These rocks are covered with
Loose rocks formed with fragments of different species due to destruction (weathering, erosion) surface. Fragmental fluid material formed of water, ice, wind drift in the sea lakes, reducing land. Thus fragments of different size and shape broken, crushed, smoothed. It formed gravel, pebbles, gravel, sand, clay. At the bottom of oceans and seas, where most settle loose material under pressure all new and new layers and compacted it become a much more solid sedimentary rock. So sand becomes sandstone, Clay - shales.
Organic species consist mostly from the remnants of organisms - the remains of dead plants and animals collected millions of years on the bottom of reservoirs. For example, chalk and limestone formed from the shells of marine organisms and armor. Angle formed dead tree that grew millions of years ago. A peat and is now produced in marshes of herbaceous plants. Organic origin and are oil, flammable gases, amber.
Chemical species - Is a consequence loss of substances in the sediment from water solutions. This fall and accumulate on the bottom stone reservoirs and potassium salts. Are formed from aqueous solutions as gypsum, flint, dolomite and others.
Space aliens sedimentary
Interestingly, that some sedimentary rocks on Earth have cosmic origins. According scientists, every day on the surface of our planet from space settles from 1000 to 1910 000 tonnes of cosmic dust. Thus, recruitment firm crust matter from space carried out continuously.
Metamorphic breed.The word "Metamorphism" means "transformation". Conversion from rocks occurs when conditions change in their occurrence compared with those of which they formed. Yes, because of the slow arching sedimentary crust and magmatic rocks are buried under new layers thickness. They find themselves at a great depth under high temperatures and pressures. Then breed heated, compressed and transformed (metamorfizuyutsya) - Acquire new properties. For example, loose sand becomes hard quartzite, fragile limestone - a solid marble, granite - gneiss. Rocks that have undergone these changes are called metamorphic.
At raising the earth's crust metamorphic and igneous rocks end up on the surface. Then they collapse and become loose sedimentary rocks.
Types the crust.Different rocks originally deposited layers and form like "floors" the crust. However, their ratio in it different. According distinguish between two types of crust: continental and oceanic.
Inland terrestrial barkhas a "three-storey 'structure of sedimentary, granite and basalt layers. Sedimentary layer (thickness of 1 mm to 20 km) forms a surface on which we walk. Species layers are deposited in it, changing each other. Granitic layer (10-20 km) than magmatic rocks (granites) and metamorphic form (gneiss, marble etc.).. Among them the oldest rocks of our planet - gneiss, aged about 4 billion years. In the basalt layer (15-25 km) is dominated magmatic rocks: basalts occur along with labradorite, gabbro.
Oceanic Earth barkformed only two layers - sedimentary (1 km) and basalt (5-10 km). Layer of granite there is almost no sedimentary and less powerful. This type of bark is only when zapadynamy oceans.
Thus, Earth crust is a complex and diverse. This is different conditions for its formation and the different processes that occur in it.
Fig. Types of Earth crust
Questions and Tasks
1. What substances prepared crust?
2. Which groups share the Origin rocks?
3. How do igneous rocks formed?
4. Which groups are divided sedimentary rocks?
5. What is called metamorphic rock?
6. Select two major markers that continental crust is different from the ocean.