3. Continental and oceanic earth’s crust
THE CRUST. The crust covers the mantle and is the earth's hard outer shell, the surface on which we are living. Composition includes oxygen, silicon, aluminum, calcium, iron, sodium, potassium, and magnesium. Relative Temperature varies from air temperature to 870C. Density: 2.5 to 3.0 times denser than water.
What does the crust consist of? Oceanic crust is below the oceans. There, the crust is 4-7 miles (6-11 km) thick. The rocks of the oceanic crust are very young compared with the rocks of the continental crust. The rocks of the oceanic crust are not older than 200 million years.
Continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores. You can divide this land into six big pieces, which are called continents. (Eurasia (Europe and Asia together), Africa, North-America, South-America, Antarctica and Australia).
Earth's crust is divided into 15 major tectonic plates: the North American, Caribbean, South American, Scotia, Antarctic, Eurasian, Arabian, African, Indian, Philippine, Australian, Pacific, Juan de Fuca, Cocos, and Nazca plates. Tectonic plates actually slide around on the mantle, causing earthquakes, mountain formation, continental drift, volcanoes, and other geologic activity on the crust.
The earth's crust is the thickest below the continents. The continental crust is older than the oceanic crust. Some rocks are 3.8 billion years old.
Layer of the sedimentary rock is situated in the top part of the earth’s crust, and below there are granitic and basaltic layers. There is no granitic layer in the oceanic earth’s crust; layer of the sedimentary rock is rather thin. The Earth’s crust has a transitional character in the border regions of continental and oceanic crust. Such structure of the Earth’s crust occurs in the border part of Eurasia with the Pacific Ocean. Island arcs and deep oceanic channels that are situated along this arc serve as proof of it. Plain and platform regions occupy about 53% of land. The largest world plains are – East European, West Siberian, the Great Plain of China, the Great and Central plains of America, Amazonian, La Plata in South America and others.
Most mineral resources are derived from the Earth’s crust. The crust is composed of minerals that are crystalline solids with specific and rather simple composition. Minerals in the Earth’s crust are concentrated into specific groups which are called rocks. The oceanic floor consists largely of minerals rich in calcium, magnesium, iron and silicon, and it is formed by the cooling of floor to form a type of rock called basalt. It is subjected to the same forces of erosion and weathering. The continental crust contains less iron and magnesium than the oceanic crust, but relatively more silicon, aluminium, sodium and potassium. The continental crust is more complicated and has a more variable thickness and a less well defined structure.
There are two principal types that predominate:
1) Igneous rocks which are formed by the cooling and crystallization of liquids from deep in the crust called magma;
2) Sedimentary rocks which are formed by sedimentation and gradual cementation of sediments by the action of water, ice, wind and organisms. They are layered and stratified. Continental crust contains extremely varied types of rock. The oceanic crust shows little variation in composition.
Thin Crust. Earth's crust is only 40 kilometers (25 miles) thick on average, making it the thinnest of Earth's three layers of crust, mantle, and core. This thin band contains all known life in the universe.
Lesson 2
Тheme 2: Atmosphere and climate
Plan:
Structure of atmosphere
Atmospheric circulation
Climate and its classification