Structure of the Earth

The crust and the solid upper part of the upper mantle together form the lithosphere, a rigid, solid layer. Below the lithosphere is the asthenosphere, a deformable, plastic solid or magma layer that is more fluid due to higher temperatures and lower pressure compared to deeper layers.

In the lower mantle, increased pressure makes the molten rock less fluid, or 'thicker,' compared to the asthenosphere. The deeper one goes, the more pressure is exerted by the overlying rock due to gravity.

The Earth's crust, divided into continental and oceanic crust, varies in thickness from 30 to 60 kilometers. The continental crust is generally thicker than the oceanic crust. The crust is chemically distinct from the mantle, primarily defined by its composition.

The mantle is approximately 2,900 to 3,000 kilometers thick, significantly deeper than the crust. It is subdivided into the upper mantle and the lower mantle, with the upper mantle extending about 700 kilometers down.

The core is composed mainly of nickel and iron, with heavier elements having sunk to the center during Earth's formation. The outer core is about 2,300 kilometers thick and is liquid due to high temperatures and relatively lower pressure. In contrast, the inner core, approximately 1,200 kilometers thick, is solid despite extremely high temperatures because immense pressure prevents its molecules from flowing, demonstrating a mechanical difference rather than a chemical one.