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Heat in the Earth's Interior

Overview

  • Group 1 - Astell discusses the internal heat dynamics of the Earth.

Objectives

  1. Causes of Heat: Explain what causes heat in the Earth's interior.

  2. Different Strata: Evaluate the different layers and their characteristics.

  3. Heat Distribution: Explain how Earth's internal heat is distributed.

Layers of the Earth

Structure

  • Inner Core:

    • Extremely dense, consists of solid iron, very hot (close to sun's surface temperature).

    • Immense pressure keeps the outer core liquid.

  • Outer Core:

    • Composed of liquid iron and nickel.

    • Heavily influenced by radioactive decay with turbulent currents.

  • Mantle:

    • Thickest layer composed of iron, magnesium, and silicon.

    • Dense, hot, semi-solid; partially melted rock near the surface.

  • Crust:

    • Extremely thin, cold, and brittle compared to lower layers.

    • Broken into tectonic plates along with the upper mantle.

Earth's Sources of Heat

Primordial Heat

  • Formation Heat:

    • Generated during the accretion of materials from planetesimals, converting kinetic energy to thermal energy.

  • Adiabatic Compression:

    • Increased gravitational load compresses particles at the center.

  • Core Formation:

    • Settling of iron generates significant heat during differentiation.

  • Decay of Short-lived Radioisotopes:

    • Examples: Beryllium-10, Aluminum-26 - these were significant in the early solar system.

Radiogenic Heat

  • Long-lived Radioisotopes:

    • Examples include Uranium-235, Uranium-238, Potassium-40, and Thorium-232.

    • Major contributors to heat, especially in early Earth's history.

Gravitational Pressure

  • Increases with depth, leading to significant pressure (3-4 million times atmospheric pressure).

  • Rocks act as insulators, trapping heat, leading to melting of materials.

Dense Core Materials

  • Density rises towards the center, containing heavy elements like gold and platinum.

  • Iron-rich material descending generates about 2,000 Kelvin of heat.

Distribution of Earth's Internal Heat

Mechanisms of Heat Transfer

  • Convection:

    • Efficient heat transport in the fluid outer core and mantle.

    • Dominant in zones of molten rock; minimal in transition zones.

  • Conduction:

    • Governs thermal conditions in solid portions of the Earth.

    • Heat is transmitted through atomic or molecular collisions, transferring heat from the core to the surface.

Formation of Magma

Magma Characteristics

  • Composed of molten rocks beneath Earth's surface.

  • Creates igneous rocks once solidified; found in volcanic magma chambers.

Magma Formation Processes

  1. Partial Melting:

    • Occurs as different minerals melt at varied temperatures due to rock composition.

  2. Decompression Melting:

    • Happens as rock moves to lower pressure zones near the surface without temperature changes.

  3. Flux Melting:

    • Introduces water or carbon dioxide to lower melting points, thereby facilitating partial melting.

Assessment Questions

Multiple Choice

  1. Temperature Trend: a. Increases from crust to core.

  2. Source of Heat: a. Decay of radioactive elements.

  3. Magma Movement Process: A. Decompression melting.

True or False

  1. Convection Relation: False, convection does not occur between mantle and core.

  2. Magma vs Lava: True, lava is erupted; magma is stored.

  3. Pressure in Crust: False, greatest pressure is found deeper than the crust.

  4. Partial Melting Temperature: False, the temperature increases.

  5. Melting Influences: True, they affect the melting of rocks.