The Earth is composed of four main layers from outermost to innermost: the crust, mantle, outer core, and inner core. The crust is the top layer and is divided into continental and oceanic crust of varying thicknesses and compositions. Below the crust is the mantle, which makes up over 80% of the Earth's volume and contains silicate rocks. The mantle is divided into the lithosphere, asthenosphere, and mesosphere. The outer core is made of liquid iron and nickel, while the inner core is solid due to extreme pressure.

1. Layers of the Earth
Crust
Mantle
Outer Core
Inner Core

2. Crust
•Avg. thickness- 35 km
•2 kinds
1. Continental
20-90 km thick; known as
sial; contains older rock,
primarily granite; less
dense than oceanic crust
2. Oceanic
5-10 km thick; known as
sima; younger rock,
primarily basalt; more
dense crust

3. Crust Cont.
•All life exists in the crust of the
Earth.
•Approximately 90 different
elements are found in the crust,
but 5 make up 90% of the crust-
oxygen, silicon, aluminum,
iron, & calcium
•Sodium, potassium, &
magnesium are the most
common elements in the
remaining 10%

6. Mantle
Earth’s mantle contains 80% of
Earth’s volume & 67% of Earth’s
mass.
Common elements found in the
mantle are: silicon, oxygen,
aluminum, iron, & magnesium.
The mantle consists of solid rock,
except for the asthenosphere.
Density increases in the mantle as
depth increases

7. Layers of the Mantle
The mantle is divided into 3
sections.
1. Lithosphere- consists of the
uppermost part of the mantle
(rigid rock) & the crust.
Average thickness is 100 km.
- Moho’s discontinuity- boundary
separating crust from mantle;
discovered in 1909 using
seismic data; found
approximately 30 km from
Earth’s surface

8. Layers of the Mantle cont.
2. Asthenosphere- 100-250 km
deep; more fluid layer, but not liquid
3. Mesosphere- lowest layer; rigid
rock; 660-2900 km deep
-temperature increases with depth,
as does density

10. Core
Diameter of the total core is 6960
km = to approximately the diameter
of Mars
The core is 1/6 of Earth’s volume &
1/3 of its total mass

11. Outer Core
•Approximately 2270 km thick
•Temperature approximately 4000-
5000º Celsius
•Liquid; very dense molten iron &
nickel
•Believed to create Earth’s
magnetic field; similar to the
magnetic field around a magnet

12. Inner Core
•Temperature is about 5000º Celsius
•Believed to be solid; very dense iron
& nickel
•Remains solid due to immense
pressure (may be 2 million times
stronger than normal pressure
exerted on Earth’s surface);
molecules can not spread out &
become liquid