1. The Early Earth “Mr. Montgomery’s Early Earth PowerPoint redefines PowerPoint excellency” - PPTA

2. Formation of Earth

3. Earth’s Heat Sources 1. Heat of Formation a) The Great Bombardment – Impacts of asteroids and meteors created huge amounts of thermal energy. b) Gravitational contraction – as the Earth formed it accumulated more and more rocky bodies, growing in size and mass. ▪ More mass = increased gravity = increased temperature 2. Radioactivity – decay of radioactive isotopes such as Uranium-238 releases energy in the form of heat.

4. Early Earth Differentiation – process of heavy materials sinking toward the center and lighter materials staying near the surface of a planet.

5. Early Earth About 4 billion years ago semi-permanent crust formed

6. Earth’s layers: Composition ▪ Crust: Made of Oxygen, Silicon, Aluminum ▪ Mantle: More magnesium, less aluminum & silicon than the crust ▪ Core: Mostly Iron

7. Earth’s layers: Physical Properties The Lithosphere ▪ The crust & rigid upper mantle: thin layer of light elements floating on top of the Earth. The Asthenosphere ▪ Viscous (thick, sticky) upper mantle. The Mesosphere ▪ Lower mantle: More dense and rigid than the upper mantle. Outer core: Liquid Inner core: Solid

8. Relative thickness of Earth’s layers

9. Convection ▪ Convection currents help distribute heat from the core to the surface.

10. So, how do we know what the mantle and core are made of?

11. 1. Core - Composition of meteorites Iron-nickel alloy Magnesium- silicate rocks

12. 2. Inclusions of the mantle in volcanic rocks The mantle

13. 3. Fragments of the upper mantle trapped in mountain belts The mantle in Oman

14. 4. Behavior of sound waves from earthquakes & large explosions Structure of Earth modeled from seismic waves Structure of fetus modeled from sound velocities