THE EARTH'S INTERIOR
Compositional layering versus Physical layering
There are two types of concentric layers based on the method used to determine them:
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Chemical Composition and
Physical Properties.
COMPOSITONAL LAYERS OF THE EARTH'S INTERIOR
By composition, the layers from the surface to the interior are:
CRUST, MANTLE, CORE : 3LAYERS
The crust is the thin outer solid surface that makes < 1% of earth's volume. There
are 2 types: continental and oceanic. The continental crust has the composition of
granite rock and lower density (2.7 g/cm cubed). The ocean crust has basaltic
composition, and it is slightly denser (2.9).
The mantle is a very thick layer beneath the crust ~ 83% of earth's volume
(approximately, 2,900 km thick). The composition of the mantle is mainly:
magnesium, silicon, and oxygen, with 4.5 (g/cm cubed) average density.
The core is the innermost layer, thicker than the mantle (3,400 km, if you combine
inner and outer core), and much denser (13 g/cm cubed). The composition is mainly
Iron (90%) + 10% Nickel, Sulfur, Silicon + Heavy Elements.
PHYSICAL LAYERS OF THE EARTH'S INTERIOR
The physical layers were determined by using physical properties of materials such
as temperature, density, plasticity, stress tolerance, etc. In general, all physical
layers of the Earth were differentiated by density, in which case, the heavier
material settled below the lighter material in layers.
There are 5 physical layers: Lithosphere, Asthenosphere, Mesosphere, Outer Core,
and the Inner Core.
1.) The Lithosphere consists of the crust and uppermost part of the mantle (less
than or equal to 100 km). Generally, this layer shows low temperatures, low density,
and it is brittle and rigid.
2.) Below is the Asthenosphere which makes up a major portion of the upper
mantle, down to ~700 km. Hot (2,000 degrees), denser, and plastic under stress.
Solid rock that is like putty or asphalt and flows very slowly. Convection Currents
occur here.
3.) Below the asthenosphere is the lower mantle or the Mesosphere. This layer is
hotter, of slightly higher density, but more rigid than the asthenosphere.
4.) Physically, the Core has 2 layers : Liquid Outer Core - very dense liquid of ~ 12
g/cm cubed and very hot (~5,000 degrees Celicus).
5.) Solid Inner Core- Slightly hotter and denser than the Outer Core. Due to the
tremendous pressure from the overlying weight, the Iron-Nickel alloy composition
is prevented from melting (pressure cooker model), and therefore this layer remains
as a solid.
The flow of the liquid in the Outer Core as large convection currents creates
electrical currents which in turn creates the earth's magnetic field (Geomagnetic
Field).
Diagram of earth’s compositional and physical layers