Earth's Internal Layers Overview

Overview

This lecture explains the Earth's internal layers, detailing both their chemical composition (crust, mantle, core) and physical properties (lithosphere, asthenosphere, mesosphere, outer core, inner core).

Layers by Chemical Composition

• The Earth is divided into crust, mantle, and core based on chemical composition.
• The crust is the outermost layer; it includes continental (thicker, less dense) and oceanic (thinner, denser) types.
• The continental crust contains granite; the oceanic crust contains basalt.
• The crust is divided into about 15 tectonic plates with activity (earthquakes, volcanoes) mainly at plate boundaries.
• The mantle lies beneath the crust, is about 1,800 miles thick, and is made of silicate minerals rich in magnesium and iron.
• The core, mostly iron and nickel, is the densest layer and makes up about one-third of Earth’s mass.
• The outer core is liquid, mainly iron and nickel, about 1,400 miles thick, and extremely hot (7,200–9,000°F).
• The inner core is solid iron, even hotter (9,000–13,000°F), about 755 miles thick, kept solid by very high pressure.

Layers by Physical Properties

• Physical layers include: lithosphere, asthenosphere, mesosphere, outer core (liquid), inner core (solid).
• The lithosphere is the rigid outer layer (includes crust and upper mantle) and forms tectonic plates (~100 km thick).
• The asthenosphere, beneath the lithosphere, is solid but plastic and can slowly flow; tectonic plates move atop it.
• The mesosphere is the strong lower mantle; its rocks flow slower than in the asthenosphere.
• The outer core is liquid and surrounds the solid inner core at Earth's center.

Key Terms & Definitions

• Crust — Earth’s outermost, solid chemical layer.
• Mantle — Layer beneath the crust, composed of silicate minerals with more magnesium and iron.
• Core — Central layer of Earth, mostly iron and nickel, includes outer (liquid) and inner (solid) sections.
• Lithosphere — Rigid outer physical layer, includes the crust and upper mantle.
• Asthenosphere — Soft, slowly flowing layer beneath lithosphere; tectonic plates move on it.
• Mesosphere — Strong, lower portion of the mantle below the asthenosphere.
• Tectonic Plates — Large, moving sections of the lithosphere causing geological activity.

Action Items / Next Steps

• Review the differences between chemical and physical layers of the Earth for the next quiz.
• Memorize key layer properties and definitions.