LESSON-2-EARTHS-INTERNAL-HEAT-LAYERS-OF-THE-EARTH

Earth's Internal Heat

• Understanding of Earth's internal heat is crucial as it leads to volcanic activity, continent movements, mountain formation, and earthquakes.

Source of Internal Heat

Overview

• The heat within the Earth is derived from three primary sources:

  • Primordial Heat: leftover heat from Earth's formation.

  • Radiogenic Heat: heat from the decay of radioactive elements.

  • Gravitational Pressure: heat generated due to pressure at deeper layers.

Formation and Heat Distribution

Geological History

• Earth formed approximately 4.6 billion years ago.

• The temperature of the Earth varies across its layers, increasing from the crust down to the inner core.

Layered Structure and Heat Retention

• Earth's layers manage heat differently:

  • Primordial heat stems from gravitational energy attracting gas and dust which formed planetesimals.

  • Initially, Earth was molten, which resulted in heat being trapped in the core.

  • The primordial heat is preserved as it takes time for heat to escape to the surface.

Types of Internal Heat

1. Primordial Heat

• Definition: Heat released during Earth’s early formation.

• Result of accretion, where gravitational energy compacted gas and dust.

• Initially leads to a molten state in the Earth's core.

• Retained heat contributes to current temperature within the Earth.

2. Radiogenic Heat

• Key Isotopes:

  • Potassium-40 (K40)

  • Thorium-232 (Th232)

  • Uranium-235 (U235)

  • Uranium-238 (U238)

• Formed from the decay of these isotopes, producing heat that prevents the Earth from completely cooling.

• Heat release from radioactive decay is a continuous process, adding to internal energy.

3. Gravitational Pressure

• Effect of Pressure: Increased pressure leads to higher temperatures at greater depths.

• Center experiences pressure up to 364 GPa.

• Rocks are good insulators, minimizing heat loss from the inner Earth, leading to heat accumulation within.

• At high temperatures, material may melt, acquiring solid-like properties under pressure.

Earth's Layers

Crust

• Thin outermost layer (1% of Earth's total mass).

• Contains the brittle, fractured upper portions where earthquakes frequently occur.

Mantle

• Thickness: Largest layer, divided into upper and lower sections.

• Upper mantle: Contains the asthenosphere, where magma is stored and can flow.

• Lower mantle: Very thick, with molten rocks moving in convective patterns.

Core

• Comprised of a fluid outer core and a solid inner core.

• Outer core generates Earth’s magnetic field due to the movement of iron.

• Inner core's extreme pressures prevent iron from being in a liquid state, resulting in solid metals under high temperatures.

Thermal Properties of Layers

• Temperature, pressure, and density increase with depth:

  • Crust: solid and brittle; relatively cool.

  • Mantle: gradients from 200°C to 4000°C as you progress deeper.

  • Outer Core: liquid, with extreme temperatures (over 4000°C).

  • Inner Core: solid, very dense due to pressure (12,600 - 13,000 kg/m³).

Conclusion

• The interconnected processes of heat retention, radioactive decay, and gravitational pressure shape the dynamic nature of Earth’s internal heat. Understanding these factors is essential in explaining geological phenomena and the planet's evolution.