The Structure of Earth

 The Earth's Structure: Simple Notes

• Why study Earth's insides? To understand landforms on the surface, we need to know what's inside the Earth.

• How do we know about Earth's insides? We can't dig that deep, but we learn from:

  • Volcanoes: They bring up stuff from inside.
  • Earthquake waves: How they travel tells us about different layers.
  • Deep mines: Going down into the Earth.
  • Crustal borings: Drilling into the Earth's crust.

• Earth's Layers (like an onion!): Earth is made of layers, one inside the other. Think of Figure 15.

  1. Crust (Lithosphere): The outermost layer, the "skin" of the Earth. It's made of two parts:

     • Upper Crust (Sial):
       • Makes up the continents (land we live on).
       • Made of granitic rocks.
       • Main minerals: Silica and Alumina (that's why it's called "sial").
       • Lighter - density about 2.7.
     • Lower Crust (Sima):
       • Makes up the ocean floors.
       • Made of basaltic rocks.
       • Main minerals: Silica, Iron, and Magnesium (that's why it's called "sima").
       • Denser - density about 3.0.
     • Crust Thickness: Not the same everywhere.
       • Thin under oceans: 3-4 miles.
       • Thick under continents: up to 30 miles.
     • Continents "float" on Sima: Because sial is lighter than sima, continents are like they are floating on a sea of sima (see Figure 16).

  2. Mantle (Mesosphere): Layer under the crust.

     • Thickness: About 1,800 miles thick.
     • Made of very dense rocks.
     • Rich in a mineral called olivine.

  3. Core (Barysphere): The innermost layer, at the very center.

     • Radius: About 2,160 miles wide (from center to edge).
     • Made mostly of Iron (Fe) and some Nickel (that's why it's called "nife").
     • Temperature: Super hot, maybe 3,500°F!
     • Pressure: Extremely high.
     • State: Scientists used to think it was liquid because of heat and pressure.
     • New idea: Earthquake studies suggest the very center (innermost part) of the core might actually be solid (crystalline).

• Other parts around the Earth:

  • Hydrosphere: Oceans and seas that cover parts of the Earth's crust. All the water on Earth.

  • Atmosphere: Mass of gases that surrounds the Earth like a blanket, going up over 15 miles into the sky. The air we breathe.

In Simple Words: Earth is like a layered ball. It has a thin outer "skin" called the crust (made of lighter continents and denser ocean floors). Under the crust is a thick layer called the mantle. In the very center is the core, which is mostly iron and nickel and super hot. Oceans cover parts of the crust, and air surrounds the whole thing as the atmosphere.