Earth's Layers Overview

Overview

This lecture explains the Earth's layers based on both chemical composition and physical properties, describing key features of each.

The Earth is divided into the crust, mantle, and core based on chemical composition.
The crust is the outermost layer and includes continental (thicker, less dense, granite) and oceanic (thinner, denser, basalt) types.
The crust is 25 miles (40 km) thick on average and forms 15 tectonic plates.
The mantle lies beneath the crust, is 1,800 miles (2,900 km) thick, and is composed of silicate minerals richer in magnesium and iron.
The core, Earth's innermost layer, is mostly iron and nickel, extremely dense, and makes up about 1/3 of Earth's mass.
The outer core is liquid (iron and nickel), about 1,400 miles (2,300 km) thick, and very hot (7,200–9,000°F).
The inner core is solid, primarily iron, about 755 miles (1,200 km) thick, and even hotter (9,000–13,000°F).

The five physical layers are the lithosphere, asthenosphere, mesosphere, outer core, and inner core.
The lithosphere (crust + upper mantle) is rigid, about 100 km thick, and divided into tectonic plates.
The asthenosphere lies below the lithosphere, is semi-elastic, and allows plates to move above it.
The mesosphere is the lower mantle, where rock flows more slowly than in the asthenosphere.
The outer core is liquid, and the inner core is solid and extends to the Earth's center.

Crust — Earth's outermost, rocky shell; divided into continental and oceanic types.
Mantle — Thick, solid, silicate rock layer beneath the crust, rich in magnesium and iron.
Core — Central layer of Earth, mainly iron and nickel; includes liquid outer core and solid inner core.
Lithosphere — Rigid outer layer (crust and upper mantle), forming tectonic plates.
Asthenosphere — Semi-elastic, slow-flowing solid rock beneath the lithosphere.
Mesosphere — Lower mantle where rock flow is slower.
Tectonic Plates — Large, rigid pieces of the lithosphere moving over the asthenosphere.