Inside the Earth
The Earth is divided into three layers – the crust, the mantle, and the core. The layers are based on the compounds that make
up each layer. Less dense compounds make up the crust and mantle and the densest compounds make up the core.
The Crust
The outermost layer of Earth is the crust. The crust is 5 to 100 km (3.1 – 62.1
mi) thick. It is the thinnest layer. There are two types of crust – oceanic and
continental. Oceanic crust is denser than continental crust.
The Mantle
The layer of the Earth between the crust and core is the mantle. The mantle is
thicker than the crust and contains most of the Earth’s mass. You cannot
reach the mantle because the crust is too thick to drill through. We can only
speculate what the composition and other physical properties of the mantle
are like. The mantle is 2,900 km (1,802 mi) thick.
The Core
The layer that extends from below the mantle to the center of the Earth is the
core. Scientists think that the Earth’s core is made mostly of iron and some
nickel. The core is roughly 1/3 of the Earth’s mass. The core has a radius of
3,430 km (2,131 mi).
Physical Structure of the Earth
The Earth is divided into 5 physical layers, - the lithosphere, asthenosphere, mesosphere, outer core, and inner core.
Lithosphere – This is the outermost, rigid layer of the Earth. It is made up of the crust and the rigid upper part of the mantle.
The lithosphere is divided into tectonic plates. It is 15 - 300 km (9.3 – 186 mi) thick.
Asthenosphere – This is a plastic layer of the mantle on which pieces of the lithosphere move. The asthenosphere is made of
solid rock that moves very slowly. It is 250 km (155 mi) thick
Mesosphere – This layer is beneath the asthenosphere. It is the strong lower part of the mantle. This layer extends from the
bottom of the asthenosphere to the Earth’s core. It is 2,550 km (1,585 mi) thick.
Outer Core – This is the liquid layer of the Earth that lies beneath the mantle and surrounds the inner core. It is 2,200 km
(1,367 mi) thick.
Inner Core – The inner core is the solid, dense center of the Earth. It extends from the bottom of the outer core to the center of
the Earth. It is 1,230 km (764 mi) thick.