Earth's Internal Structure

Overview

This lecture explains the internal structure of the Earth, the properties of each layer, and how scientists have determined these features using different methods.

Earth's Layers Overview

• The Earth is structured in layers: crust, mantle, outer core, and inner core.
• The crust is the outermost and thinnest layer, followed by the thick mantle, then the core (outer and inner).

The Crust

• The crust ranges from 6 to 70 km thick, much thinner compared to other layers.
• There are two types: continental crust (forms land, thicker, older, less dense, mostly granite) and oceanic crust (under oceans, thinner, younger, more dense, mostly basalt).
• Continental crust is made mainly of silicates and aluminum (SIAL), while oceanic crust is silicates and magnesium (SIMA).

The Mantle

• The mantle is about 2,900 km thick and is the thickest layer.
• Composed of semi-solid (viscous) magma that moves in convection currents.
• Convection currents in the mantle drive movement of crustal plates, leading to continental drift and geological activity.

The Core

• The outer core is 2,260 km thick, liquid, mainly iron and nickel, and temperatures reach 4000-5000°C.
• Movement in the outer core creates Earth's magnetic field.
• The inner core has a radius of 1,220 km, is solid due to high pressure, and reaches 5200°C, close to the temperature of the sun's surface.

How We Know Earth's Structure

• Surface methods: drilling, studying rocks, volcanoes, and lava composition, though drilling only reaches the crust.
• Main method: analyzing seismic waves from earthquakes, which change speed/direction in different materials, revealing layer properties.

Key Terms & Definitions

• Crust — The Earth's outermost, thinnest solid layer.
• Continental Crust — Thick, less dense, older crust forming continents.
• Oceanic Crust — Thin, denser, younger crust under oceans.
• Mantle — Thick, semi-solid layer beneath the crust with convection currents.
• Core — Central part of the Earth, divided into a liquid outer core and solid inner core.
• Convection Currents — Circular magma movements in the mantle caused by heat from the core.
• Seismic Waves — Vibrations from earthquakes used to study Earth's internal layers.

Action Items / Next Steps

• Review the differences between continental and oceanic crust.
• Study diagrams showing Earth's layered structure.
• Read about how seismic waves are used to investigate Earth's interior.