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Chapter 2, Section 1 The Earth Inside and Out • The earth is the 3rd planet in our solar system, which is part of the Milky Way galaxy. •The earth is 93 million miles away from the sun. •The earth is about 24,900 miles in circumference, and about 7,000 miles in diameter. Inside the Earth • The core is the center of the earth – made of iron and nickel. – Inner core is solid (760 mile radius). – Outer core is liquid (1,380 miles thick). • The mantle surrounds the core (1,800 miles thick) and makes up most of the earth’s mass. – Magma forms in the mantle and can break through the earth’s crust. • The crust is the thin layer of rock at the earth’s surface (19-37 miles thick). On and Above the Earth • Atmosphere – The layer of gases surrounding the earth; contains the oxygen we breathe, protects the earth from radiation and space debris, and provides the medium for weather and climate. • Lithosphere – The solid rock portion of the earth’s surface, the crust and the uppermost mantle. The continents and seafloor are found here. On and Above the Earth • Hydrosphere – All the water on the earth – oceans, seas, rivers, lakes, and water in the atmosphere. • Biosphere – The part of the earth where plants and animals live. Continental Drift • Continental Drift hypothesis was originated by Alfred Wegener of Germany in 1912. • Maintained that the earth was once a supercontinent – Pangea or Pangaea – that split and drifted away millions of years ago. • Surrounded by an ocean called Panthalassa.