Unit 2: Earth's Interior and Systems

Interior of the Earth

We cannot drill to the center of the Earth. Our knowledge of its interior comes *indirectly* from studying seismic waves (earthquake waves), which change speed and direction as they pass through different materials.

The Earth's interior is divided into layers based on chemical composition and physical properties.

Chemical Layers (What it's made of)

• Crust: The outermost, very thin, rocky layer.
  • Continental Crust: Thicker (30-70 km), less dense, granitic composition.
  • Oceanic Crust: Thinner (5-10 km), denser, basaltic composition.
• Mantle: The thickest layer (~2900 km). Composed of hot, dense silicate rock (peridotite).
• Core: The center of the Earth. Composed of a dense iron-nickel alloy.

Physical Layers (How it behaves)

This is a more detailed view that explains processes like plate tectonics.

• Lithosphere: The rigid, brittle outer layer. It includes the crust AND the uppermost solid part of the mantle. This is the layer that is broken into tectonic plates.
• Asthenosphere: A weak, "plastic-like," semi-molten layer in the upper mantle, just below the lithosphere. The lithospheric plates "float" or move on this layer.
• Mesosphere: The rest of the mantle, which is solid but can slowly flow (convect) over geological time.
• Outer Core: Liquid iron-nickel. The flow of this liquid metal generates the Earth's magnetic field.
• Inner Core: Solid iron-nickel. It is solid (despite being hotter) because of the immense pressure.

Earth's Spheres

Earth is a complex system of interacting parts, which are often grouped into four "spheres".

1. Lithosphere

The "rock sphere." This is the solid, rocky part of the Earth, including the crust and upper mantle. It provides the foundation for life and is the source of all minerals and soils.

2. Hydrosphere

The "water sphere." This includes all of Earth's water, in all its forms:

• Liquid: Oceans, rivers, lakes, groundwater.
• Solid: Ice caps, glaciers, permafrost.
• Gas: Water vapor in the atmosphere.

3. Atmosphere

The "vapor sphere." This is the thin blanket of gases that surrounds the Earth, held in place by gravity. It is composed mainly of Nitrogen (78%) and Oxygen (21%). It protects life from harmful solar radiation and regulates climate.

4. Biosphere

The "life sphere." This includes all living organisms on Earth, from microbes and plants to animals. The biosphere exists in, and interacts with, all the other spheres (e.g., life in the soil, in the oceans, and in the air).

Interrelationship of Earth's Spheres

No sphere exists in isolation. They are all deeply interconnected, and a change in one will affect all the others. This is the basis of Earth System Science.

Examples of Interrelationships:

• Volcanic Eruption:
  • The Lithosphere (magma) erupts...
  • ...spewing gases (e.g., SO₂) into the Atmosphere (affecting climate)...
  • ...and ash which settles on land, affecting the Biosphere (plants/animals) and water quality (Hydrosphere).
• Formation of Soil:
  • Rain (Hydrosphere) and air (Atmosphere) chemically weather rock (Lithosphere).
  • Organisms (Biosphere) die and decay, adding organic matter to create fertile soil.
• The Water Cycle: The sun heats the Hydrosphere (oceans), causing evaporation. This water vapor (Atmosphere) condenses into clouds, moves over the Lithosphere, and precipitates as rain, where it is used by the Biosphere.

Exogenetic and Endogenetic Processes

These are the two main categories of geological processes that shape the Earth's surface.

Exogenetic (or Exogenic) Processes

Exogenetic Processes: Geological processes that operate on or near the Earth's surface. They are "external" processes powered primarily by energy from the Sun.

• Primary Function: To wear down the Earth's surface (a process called denudation). They are "destructive" forces that work to level the land.
• Examples:
  • Weathering: The in-place breakdown of rock (physical or chemical).
  • Erosion: The removal and transport of weathered material.
  • Agents of Erosion: Running water (rivers), wind, glaciers (ice), and gravity (landslides).

Endogenetic (or Endogenic) Processes

Endogenetic Processes: Geological processes that originate deep inside the Earth. They are "internal" processes powered by Earth's internal heat.

• Primary Function: To build up and create new landforms. They are "constructive" forces.
• Examples:
  • Volcanism (Igneous Activity): Magma rising to the surface to form volcanoes and lava flows.
  • Tectonics (Plate Tectonics): The movement of the lithospheric plates.
  • Mountain Building (Orogeny): Plates colliding to push up mountains.
  • Earthquakes: The sudden release of internal stress.
  • Metamorphism: Changing rocks with heat and pressure.