Earth and Moon

Earth's crust

Earth's crust

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Earth is one of the solid planets or, at least, solid crust, since not all layers are.

If we make a cut that crosses the Earth through the center we will find that, under the crust, there are several layers whose structure and composition varies greatly.

Above we have the atmosphere, a layer of gases we call air, formed in turn by a series of layers, which functions as a protective shield of the planet, maintains the temperature and allows life. Water, lots of liquid water accumulates in the slits and low areas of the crust and, at the poles, frost.

Inner layer Approximate thicknessPhysical state
Cortex7-70 kmSolid
Upper mantle650-670 kmPlastic
Lower mantle2,230 kmSolid
External nucleus2,220 kmLiquid
Internal core1250 kmSolid

As seen in the table, below the crust there are a series of layers in a pasty state, very hot, and with an increasing density until reaching the Earth's core, again, solid, metallic, dense, ...

Earth's crust

The earth's crust has a variable thickness that reaches a maximum of 75 km below the Himalayas and is reduced to less than 7 km in most of the deep areas of the oceans.

The surface layer is formed by a set of sedimentary rocks, with a maximum thickness of 20-25 km, which forms at the bottom of the sea at different stages of geological history. The oldest age of these rocks is up to 3.8 billion years. Below there are granite type rocks, formed by cooling magma.

It is estimated that, under mountain systems, the thickness of this layer is more than 30 km. The third rock layer is formed by basalts and has a thickness of 15-20 km, with increases of up to 40 km.

The continental crust is different from the oceanic. Unlike the continental crust, the ocean is geologically young in its entirety, with a maximum age of 180 million years.

Here we also find three layers of rocks: the sedimentary, of varying width, formed by the constant accumulations of rock fragments and organisms in the oceans; that of the basalt 1.5 to 2 km thick, mixed with sediments and with rocks of the lower layer and a third layer consisting of rocks of the type of the gabbro, similar to the basalt in composition, but of deep origin, which has about 5 kilometers of thickness.

It seems that the oceanic crust is due to the cooling of magma from the upper mantle.

On the next page we will see the mantle and the core of our planet.

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Earth: hydrosphere and atmosphereThe mantle and the core of the Earth