Earth's Interior

I. Earth’s Chemical Layers (Composition)

  • Crust: The outermost "skin."

    • Continental Crust: Thicker, made of Granite (less dense).

    • Oceanic Crust: Thinner, made of Basalt (denser).

  • Mantle: The thickest layer; made of hot silicate rocks.

  • Core: The center; made of Iron and Nickel (very dense).

II. Earth’s Physical Layers (Behavior)

  • Lithosphere: The "crust + top of mantle." It is rigid and brittle (this is what breaks into plates).

  • Asthenosphere: The "upper mantle." It is plastic/semi-liquid. It flows slowly, moving the plates.

  • Mesosphere: The "lower mantle." It is solid and strong due to high pressure.

  • Outer Core: The only liquid layer. Its movement creates Earth’s Magnetic Field.

  • Inner Core: The very center. It is solid metal because the pressure is so high it can't melt.

Image of Earth's internal structure layers

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III. Seismic Waves (How we "see" inside)

  • P-Waves (Primary):

    • Fastest (they arrive first).

    • Move like an accordion (Push-Pull/Compressional).

    • Can travel through solids and liquids.

  • S-Waves (Secondary):

    • Slower (they arrive second).

    • Move like a snake (Side-to-Side/Shear).

    • Can ONLY travel through solids. (They stop at the liquid outer core).

IV. Key Numbers & Boundaries

  • Moho Boundary: The line between the Crust and the Mantle.

  • 2,900 km: The depth where the Mantle ends and the Core begins.

  • 6,371 km: The total distance to the center of the Earth.

  • Shadow Zones: Areas on Earth where seismographs don't pick up waves because they were bent (refracted) or blocked by the core.

Would you like me to give you a 10-question "Rapid Fire" drill just on the wave behaviors?