The Earth crust Is the outermost layer of the Earth. It is formed by a thin layer of solid rock that contains a large amount of molten rock and is a part of the planet that has cooled and solidified.
The Earth consists of four concentric layers: inner core, outer core, mantle and bark. The latter is composed of tectonic plates, which are in constant motion.
The crust of the Earth is about 30 km thick, although in the ocean floor, the thickness of the crust may be 5 kilometers. The entire bark occupies only 1% of the Earth's volume and can be divided into: the continental crust and the oceanic crust.
Parts of the Earth's crust
The oceanic crust
The oceanic crust is the part of the earth's crust that covers the ocean basins. It is composed of dark colored rocks composed of basalt.
This stone is composed of silicon, oxygen and magnesium being the density of the oceanic crust of approximately 3.0 g / cm3, being its density lower.
This difference in average densities allows many natural phenomena to occur at and beneath the surface of the Earth. The oceanic crust barely floats in the mantle and suffers a peculiar phenomenon.
With age, the oceanic crust gathers a layer of chilled mantle at the bottom. This causes the two-layer structure to sink into the hot and molten mantle.
Once in the mantle, the oceanic crust melts and recycles itself and due to this process there is an absence of aged oceanic crust. This phenomenon is absent or rare in the continental crust.
In turn, the thickness of both barks also varies. But for the oceanic, the thickness is about 3 to 6 miles, (5 to 10 kilometers) being its crust thinner than the continental.
The continental crust
The continental crust accounts for 40% of the Earth's surface and is composed of granite rock that is light in color. This stone is rich in components such as silicon, aluminum and oxygen.
The density of the continental crust is much lower compared to the oceanic crust with a value of 2.6 g / cm3. Because of this difference in magma densities between the oceanic crust and the continental crust, the continents remain in their places, allowing both crusts to float in the magma.
However, the continental crust floats much freer in the magma. In this line, the continental crust is much thicker compared to oceanic.
It has a thickness that varies between 20 miles, (35 km). In the plains, up to 40 miles, which is about 70 km in the highest mountains.
Distribution
The earth's crust is divided into pieces called plates. The heat that rises and falls inside the mantle creates convection currents generated by the radioactive decay in the nucleus.
The function of the convection currents is to move the plates so that they diverge near the earth's crust. That is, where the currents of the convection converge, the plates move towards each other.
The movement of the plates, and the activity inside the Earth, is called tectonic plates and when moving originate earthquakes and volcanoes.
The point where two plates meet is called a plate boundary. Earthquakes and volcanoes are more likely to occur at or near the limits of these.
Also, Earth's plates move in different directions which are as follows:
In a tensional, constructive or divergent limit the plates are separated, in a limit of compression, destructive or convergent, the plates move towards each other, in a conservative limit or of transformation the plates glide each other and a destructive limit also Can be called collision limit.
Composition of the bark
The crust is composed of a variety of igneous, metamorphic and sedimentary rocks collected in tectonic plates.
These plates float on Earth's mantle, and it is believed that the convection of the rock in the mantle causes the plates to slide around. On average, rocks in the crust last about 2,000 million years before they slide under another plate and return to Earth's mantle.
New rocks are formed in the regions of the oceanic crust where new material is extracted from the earth between the separating plates. In comparison, rocks in the oceans are only 200 million years old.
The temperature of the crust increases as it deepens in the Earth. It begins at a cool temperature but can reach up to 400 degrees Celsius at the boundary between the bark and the mantle, while the bark is rich in some volatile elements such as alkalis (Na, K, Rb).
In general, the crust is enriched by incompatible elements (elements concentrated in melts). From its composition, we can conclude that the crust was created by the magmatism.
98.5% of the bark consists of only 8 elements and oxygen is the most abundant element of it. As a large atom, oxygen occupies ~ 93% of the volume of the crust.
The chemical elements present in the solar system, are the same that make up the earth's crust but in different proportions. The earth's crust does not have a uniform composition. On the one hand, the continental crust is much thicker with greater proportion of silica and is lighter than the oceanic crust.
In the continental crust, the radioactive isotopes are in greater proportion and the ratio of uranium / silicon is thousand times greater than that of the solar system. In the oceanic crust, the number of radioactive isotopes is smaller. Basalt contains a proportion of only 0.5 or 0.6 parts per million of uranium.
More than 90% of the crust is made up of silicate minerals. Most abundant silicates are feldspars (plagioclase (39%) and alkali feldspar (12%)). Other common silicate minerals are quartz (12%) pyroxenes (11%), amphiboles (5%), micas (5%) and clay minerals (5%).
The rest of the family of silicates comprises 3% of the bark, although only 8% of the bark consists of non silicates - carbonates, oxides, sulphides, etc. Plagioclase is the most important mineral in the bark. It is common in mafic igneous rock as the diabase sample above.
The white elongated phenocrysts in finer basaltic masses are plagioclase crystals. Black crystals belong to pyroxene (mineral augite). Both augite and plagioclase also occur in the mass of fine-grained soil. The large crystals formed slowly before the magma erupted and the rest solidified rapidly.
Plagioclase is so common because basaltic rocks and their metamorphic equivalents are widespread. Most of the oceanic crust is composed of basaltic rocks.
Olivine (green) is denser than plagioclase and pyroxene (both are present in the ground mass) and therefore sinks to the bottom of the lava flows where the accumulated olivine rocks form.
Clay minerals are too small to be shown individually, even with a light microscope you will only see mud or dust depending on whether these minerals are moist or dry.
Clay minerals are silicates that are the product of the erosion of other silicate minerals, mostly feldspars. Biotite is one of the two major mica minerals. The other is light muscovite.
Types of rock in the Earth's crust
There are three basic types of rock: igneous, sedimentary and metamorphic. Extremely common in the Earth's crust are the igneous rocks that are volcanic and are formed from molten material.
They include not only lava thrown from volcanoes but also rocks like granite, which are formed by magma that solidifies very underground. Typically, granite makes up large parts of all continents.
The seabed consists of a dark lava called basalt, the most common volcanic rock. Basalt is also found in volcanic lava flows, such as those in Hawaii, Iceland, and large parts of the northwestern United States.
Granite rocks can be very old. It is believed that some granites in Australia are more than four billion years old, although when rocks become so old, they have been altered sufficiently by geological forces that it is difficult to classify them.
Sedimentary rocks are formed from eroded fragments of other rocks or even from plant or animal remains. Fragments accumulate in low areas, lakes, oceans or deserts, and then compressed into rock by the weight of the materials that cover them.
Sandstone is formed of sand, lodolites and limestone from sea shells, diatoms, or layers of minerals that precipitate out of water rich in calcium.
Fossils are most often found in sedimentary rock, which comes in layers, called strata. Metamorphic rocks are sedimentary or igneous rocks that have been transformed by pressure, heat or the intrusion of fluids.
Heat may come from nearby magma or hot water penetrating through hot springs but may also come from subduction, as tectonic forces draw rocks deep beneath the surface of the Earth.
Marble is metamorphosed limestone, quartzite is metamorphosed sandstone, and gneiss, another common metamorphic rock, which sometimes begins as granite.
The most abundant types of rock in the crust
The rocks are divided into three large groups: igneous, metamorphic and sedimentary rocks. The oceanic crust is composed mostly of igneous basaltic rocks that are covered by a thin layer of sediments that are thicker near the margins of the continental masses.
The continental crust is much thicker and older because it is in turn much more variable and structurally very complex.
Virtually all types of rocks known to man are found in the continental crust. Even meteorites, mantle xenoliths and ophiolites (a fragment of the ancient oceanic crust) are constituents of the continental crust.
Almost three quarters of the continental crust is covered by sedimentary rocks, and almost all are covered by loose sediments (earth, sand, earth, etc.).
It is important to understand that despite being so ubiquitous on the surface, they make up only about 8% of the entire mass of the crust. The sediments are consolidated in the sedimentary rocks and the sand becomes sandstone, mud from clay to limestone, clay to clay.
Sedimentary rocks are stable only in the upper parts of the crust. The bulk of the continental crust is made of metamorphic rocks. Igneous rocks are also common on the surface in volcanically active regions, but are also found deeper in the crust as granite (mostly) intrusions.
The most important sediments are sand, clay, mud (wet clay mixture and fine sand) and calcareous mud. The generalized sedimentary rocks are limestone (2% of the crust by volume), sandstone (1.7%), clay (4.2%) that are lithic versions of the previously mentioned loose sediments.
Chemical sediments such as halite and gypsum are also important, but their total volume is clearly less than 1% of the bark. Important igneous rocks are granite, granodiorite, gabbro, basalt, diorite, andesite, etc.
It is very difficult to say what the percentage of these rocks is but important metamorphic rocks are metamorphosed from extensive sedimentary and igneous rocks.
In this line, common metamorphic rocks are shale (metamorphosed clay), shale (metallized clay, grade higher than slate), quartzite (sandstone), marble (limestone), gneiss (igneous rock or sedimentary rocks), Amphibolite (basaltic rocks).
Global Distribution
The map of terrestrial masses shows that the oceanic crust occupies most of the Earth's surface, and that the continental crust is found in the northern hemisphere.
The continental crust (sial) is much thicker under mountain ranges than under flat areas and believes that the oceanic crust (sima) lies, on the contrary, beneath continents also forming oceanic floors.
References
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