Composition of Earth
Table below shows the layers of the Earth :
Layer
Composition
Depth
Properties
Crust Oceanic crust Continental crust
Basalt
Granite
7-10 km
20-70 km
Cool, rigid, and brittle
Cool, rigid, and brittle
Lithosphere Lithosphere includes the crust and the uppermost portion of the mantle
Varies; the crust and the mantle have different compositions About 100 km
Cool, rigid, and brittle
Mantle Uppermost portion of the mantle included as part of the lithosphere Asthenosphere
Remainder of upper mantle
Lower mantle
Entire mantle is ultramafic rock. Its mineralogy varies with depth
Extends from 100-350 km
Extends from 350-670 km
Extends from 670-2900 km
Hot and plastic, 1% or 2% melted Hot, under great pressure,
And brittle
High pressure forms minerals different from those of the upper mantle
Core Outer core
Inner core
Iron and nickel
Iron and nickel
Extends from 2900-
5150 km
Extends from 5150 km to the center of the Earth
Liquid
Solid
The rate of pressure increase with depth is called the pressure gradient, and depends on the density of the overlying rock. The pressure gradient is linear in the crust, mantle and inner core because they are (mostly) composed of solids, but non-linear in the outer core because it is a liquid. A good approximation of the rate of pressure increase with depth is: 30 MPa/km in the crust and 35 MPa/km in the mantle.
The rate of temperature variation with depth is called the geothermal gradient and varies greatly with location and depth. Temperature increases at a rate of approximately 20oC/km in the upper crust (first 10 km) but then the rate decreases to only approximately 0.3oC/km below 200km due to the homogenizing effect of mantle convection. These values are highly approximate and vary widely, for instance: the mantle beneath Hawaii is significantly hotter than the mantle beneath the rest of the Pacific Ocean. To a
Layer
Composition
Depth
Properties
Crust Oceanic crust Continental crust
Basalt
Granite
7-10 km
20-70 km
Cool, rigid, and brittle
Cool, rigid, and brittle
Lithosphere Lithosphere includes the crust and the uppermost portion of the mantle
Varies; the crust and the mantle have different compositions About 100 km
Cool, rigid, and brittle
Mantle Uppermost portion of the mantle included as part of the lithosphere Asthenosphere
Remainder of upper mantle
Lower mantle
Entire mantle is ultramafic rock. Its mineralogy varies with depth
Extends from 100-350 km
Extends from 350-670 km
Extends from 670-2900 km
Hot and plastic, 1% or 2% melted Hot, under great pressure,
And brittle
High pressure forms minerals different from those of the upper mantle
Core Outer core
Inner core
Iron and nickel
Iron and nickel
Extends from 2900-
5150 km
Extends from 5150 km to the center of the Earth
Liquid
Solid
The rate of pressure increase with depth is called the pressure gradient, and depends on the density of the overlying rock. The pressure gradient is linear in the crust, mantle and inner core because they are (mostly) composed of solids, but non-linear in the outer core because it is a liquid. A good approximation of the rate of pressure increase with depth is: 30 MPa/km in the crust and 35 MPa/km in the mantle.
The rate of temperature variation with depth is called the geothermal gradient and varies greatly with location and depth. Temperature increases at a rate of approximately 20oC/km in the upper crust (first 10 km) but then the rate decreases to only approximately 0.3oC/km below 200km due to the homogenizing effect of mantle convection. These values are highly approximate and vary widely, for instance: the mantle beneath Hawaii is significantly hotter than the mantle beneath the rest of the Pacific Ocean. To a