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Topic 2.2 Learning Goals

• Describe the dynamic process in the mantle.

• Consider mantle convection in terms of Rayleigh Numbers.

• Describe the dynamic process in the core.

• Account for Earth’s magnetic field, its changes over time, and how it is recorded in rocks and sediments.

• Describe magnetic fields on other planets.

Topic 2.2 Rationale / Sample Questions / Midterm Focus Areas

• Rationale: To analyze dynamic activity in Earth's interior.

• Sample Quiz Questions: Available for practice (does not count towards course points).

• Midterm Focus: Use this section to concentrate studies for the midterm 2 exam.

Topic 2.2 Outline

• 2.2.1: The Mantle

  • 2.2.1.1: Convection

  • 2.2.1.2: Convection Models

  • 2.2.1.3: Mantle Plumes

• 2.2.2: The Core

  • 2.2.2.1: The Outer Core

  • 2.2.2.2: The Inner Core

  • 2.2.2.3: Earth's Magnetic Field

• 2.2.3: Summary

Internal Dynamics: Mantle

2.2.1 Convection

• Heat from Earth’s core warms the base of the mantle, primarily through convection.

• Convection illustrated using the example of heating soup: hot, less dense liquid rises, cools, then sinks.

• Convection can be slow: mantle moves at rates of 1-2 cm/year.

2.2.1.1 Convection Models

• Whole-Mantle Convection Model: Suggests the entire mantle undergoes convection.

• Layered Convection Model: Upper and lower mantle convect independently, due to differences in viscosity.

2.2.1.2 Mantle Plumes

• Mantle plumes are thought to originate from the lower mantle and rise as hot material, creating volcanism.

• Hawaiian Islands formed by a mantle plume associated with the core-mantle boundary.

2.2.2 The Core

2.2.2.1 The Outer Core

• The outer core, heated by the inner core, drives convection complicated by the Earth's rotation and the Coriolis effect, critical for generating Earth's magnetic field.

2.2.2.2 The Inner Core

• Solid sphere composed of iron-nickel alloy; grows slowly due to cooling.

• Inner core rotates with the Earth but can experience oscillations affecting magnetic fields.

2.2.2.3 Earth's Magnetic Field

• Generated by the movement of molten metal in the outer core.

• Protects Earth's biosphere and influences phenomena such as the Aurora.

• Magnetic field lines behave counterintuitively, emerging from the southern pole at the surface.

2.2.2.4 Magnetic Fields on Other Planets

2.2.2.4a) Venus

• Lacks a magnetic field due to slow rotation and cooler core temperature.

2.2.2.4b) Mars

• Had a global magnetic field which collapsed about 4.1 billion years ago, leading to loss of atmosphere.

2.2.2.4c) The Outer Planets

• Jupiter and Saturn possess strong magnetic fields due to rapid rotation and metallic hydrogen in their interiors.