Earth's Internal Structure Overview

Overview

This lecture explains Earth's internal structure through two perspectives: compositional (chemical layers) and mechanical (physical properties), highlighting key layers and their characteristics.

Compositional Layers of Earth

• Crust is the thin, outermost solid layer, composed of oceanic (5–10 km thick) and continental (10–70 km thick) crust.
• Oceanic crust is thinner and denser; continental crust is thicker and less dense.
• Mantle lies beneath the crust and extends to about 2,900 km deep, making up most of Earth's volume.
• Core is Earth's deepest, densest layer, mainly made of metals such as iron and nickel, beneath the mantle.

Mechanical Layers of Earth

• Lithosphere is the rigid, outer layer combining the crust and the cool, uppermost mantle (10–200 km thick).
• Lithospheric plates move on top of underlying mechanical layers.
• Asthenosphere lies below the lithosphere (up to 660 km deep), has putty-like, partially molten rock that can flow slowly.
• Mesosphere is the solid, lower mantle beneath the asthenosphere (660–2,900 km deep), made rigid by high pressure.
• Outer core (2,900–5,100 km deep) is liquid metal due to high temperatures.
• Inner core (from 5,100 km to Earth's center at ≈6,400 km) is solid metal because extreme pressure overcomes temperature.

Key Terms & Definitions

• Crust — Earth's outermost solid layer; divided into oceanic and continental types.
• Mantle — Thick, rocky layer between crust and core; different composition from crust.
• Core — Central, metallic layer of Earth, mostly iron and nickel.
• Lithosphere — Rigid layer made of the crust and uppermost mantle.
• Asthenosphere — Hot, semi-fluid mantle layer beneath lithosphere, allowing plate movement.
• Mesosphere — Solid, high-pressure region of the lower mantle.
• Outer Core — Liquid metal layer beneath mantle.
• Inner Core — Solid metallic center of Earth.

Action Items / Next Steps

• Review the differences between compositional and mechanical Earth layers.
• Prepare for discussion on plate tectonics and lithospheric plate movement.