Notes on Layers of the Earth

Layers of the Earth

  • The Earth is divided into three main layers:
    • Crust
    • Mantle
    • Core

Learning Targets

  • Understand and describe each of the three important layers of the Earth.
  • Explain the distinctive characteristics of each layer.
  • Relate convection currents to the movement of magma in the mantle.

The Earth’s Composition

  • Geosphere is made up of:
    • Crust
    • Mantle
    • Outer Core
    • Inner Core

Crust

  • General Characteristics:

    • The outermost layer, composed of light materials.
    • Thin compared to other layers (like the skin of an apple).

  • Types of Crust:

    • Continental Crust:
    • Composed mainly of granite.
    • Thicker (about 30-50 km).
    • Oceanic Crust:
    • Composed mainly of basalt.
    • Thinner (about 5-10 km).
    • Denser than continental crust.

  • Plate Dynamics:

    • Earth’s crust is broken into lithospheric plates that float on the semi-rigid asthenosphere.
    • Plates can move, leading to geological activity such as earthquakes and volcanism.

Mantle

  • Characteristics:
    • Largest layer of the Earth, made of hot, dense rock.
    • Flows like asphalt due to temperature differences.
  • Convection Currents:
    • The movement within the mantle causes tectonic plate motion.
    • Hot mantle material rises, cools, and then sinks back, creating a cycle.

Core

  • Outer Core:

    • Made of liquid iron and nickel.
    • Extremely hot and dense.

  • Inner Core:

    • Composed of solid iron and nickel due to extreme pressures.
    • Temperature is high, but the metals are in a solid state.

Convection Currents and Plate Movement

  • Convection currents in the mantle are instrumental in plate tectonics:
    • They operate like a boiling pot of soup - heated material rises, spreads, cools, and sinks back.
    • This flow moves the lithospheric plates above it.

Evidence of Plate Tectonics

  • Continental Drift Theory:
    • Proposed by Alfred Wegener, suggesting continents were once connected.
    • Evidence includes:
    • Similar fossils found on separated continents.
    • Some mountain ranges across continents match in shape and structure.

Types of Plate Boundaries

  1. Divergent Boundaries:

    • Plates move apart, creating new crust.
    • Example: Mid-Atlantic Ridge.

  2. Convergent Boundaries:

    • Plates collide, leading to mountain formation or subduction.

  3. Transform Boundaries:

    • Plates slide past each other, often causing earthquakes.

Earthquake and Volcano Activity

  • Earthquakes are common at plate boundaries due to the movement of tectonic plates.
  • Volcanoes typically form along divergent and convergent boundaries.

Plate Movement Rate

  • Lithospheric plates move at a rate of 1-10 centimeters per year (similar to fingernail growth).