The earth is
made of rocks; we cannot dig much deeper about 10 km, our knowledge of
structure of the earth is derived from the study of seismic wave. The velocity
of these waves depends on the composition of the region through which they
travel. So by determining the velocity of the waves, we can infer the
composition of the region through which they pass. The earth has multiple
layers are crust, mantle and core.
Crust:
This is the outermost rocky layer. The
rocks consist mainly of silicates; they are compounds of silicon with silicon
oxide as the basic compound. The thickness of crust is about 50 km under the
continent. The thickness of crust is not same everywhere. Under the seafloor,
its thickness is much less.
Mantle:
The layer from 50 km to the depth of
about 3000 km is called the mantle. It is rich in iron and magnesium
silicates.
Core:
The innermost
layer of the earth is called core. It is divided into two regions. The inner
core is solid metal sphere radius about 1200 km. It is almost pure iron alloy
with small amount of nickel. The inner core is surrounded by liquid metal about
2200 km. The matter here is in the fluid
state. The movement of inner core is responsible for earth magnetic field.
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