1. Earth’s Structure

2. The layers of Earth Earth is divided into 3 layers based on chemical composition. 1)Core: Dense metallic center, made up of mainly metal iron. 2)Mantle: Liquid middle layer made up of silicon, oxygen and magnesium. 3)Crust: The solid outer layer made up of silicon, oxygen and aluminum.

3. Continental and Oceanic Crust There are two types of crust: 1.Continental: is thicker 2.Oceanic: is thinner and heavier. Compared to the other layers, both types of crust are rocky, thin and fractured.

4. The Physical Structure of Earth Earth is divided into five layers based on physical properties. 1.Lithosphere 2.Asthenosphere 3.Mesosphere 4.Outer core 5.Inner core

5. Lithosphere 1.Lithosphere: cool rigid layer, made up of the crust and upper layer of the mantle. Lithosphere is divided into pieces called tectonic plates.

6. Asthenosphere 2. Asthenosphere Below the lithosphere. Made up of slow flowing solid rock. The moving rock allows for tectonic plates to move.

7. Physical Structure cont. 3.Mesosphere: Slow flowing layer beneath the Asthenosphere 4.Outer core: Layer of liquid Iron and Nickel. 5.Inner core: Solid iron and nickel, temperature is estimated to be between 4000ºC to 5000ºC

8. Mapping Earth’s Interior How can we know so much about Earth’s interior if no one has ever drilled through the crust? Earthquakes produce seismic waves, and travel thru materials at different speeds. Scientists use these waves to determine the density of each of Earth's layers

9. Continental Drift In the 1900’s,Scientist Alfred Wagner, viewed the continents as puzzle pieces. Had a hypothesis that our continents used to be one large continent. He named his hypothesis the Continental Drift Theory.

10. Evidence for Continental Drift Fossils of same plant can be found on continents that are far from each other. Location of mountain ranges with similar rocks show a pattern.

11. The Breakup of Pangaea A single continent Pangaea (many thousands of years ago). Split into two continents – Laurasia and Gondwana (thousands of years ago). Split into today's continents. Continents sometimes collided, forming mountain ranges and volcanoes.

12. Sea-Floor Spreading. When Wagner introduced his hypothesis, many scientists did not accept it because the strength needed to move Earth’s crust seemed impossible. In the 1960’s Scientist studying the ocean floor discovered identical patterns of magnetism on both sides of the mid ocean ridge. This was proof that continental drift was possible.

15. Sea-Floor Spreading cont. At a mid-ocean ridge, magma rises through fractures in the sea floor. As the magma cools it forms new sea floor. As this continues to happen, new floor is made and older floor is pushed away from the fracture. Sea-floor spreading was proven to cause continents to move.