Sponge: List the layers of the Earth’s atmosphere.

Earth’s Interior - Crust - ~15 km thick, 8 km under oceans, 20-50 km under continents, density of 3 g/cm3

Mantle - dense, but rocky material, 80% of Earth’s volume, density 5 g/cm3

Outer core - liquid density ~ 8 g/cm3 Inner core - solid density is compressed to 12 g/cm3

The inner and outer core are both the same temperature and are made of the same material: nickel and iron.

This separation of the parts of a planet (or moon) by density is called differentiation.

The Earth was molten in the past which allowed differentiation to occur. The Earth was molten due to the bombardment by other materials and radioactive decay.

The upper mantle is made of basalt (3 The upper mantle is made of basalt (3.5 g/cm3); the continents are made of granite (3 g/cm3) which can float on the mantle.

The Earth’s central core temperature is nearly equal to the Sun’s surface temperature. 5000K 8500°F

Surface Changes Plate Tectonics - the Earth is covered by surface plates which move individually. This movement was detected by comparison to quasars.

The plates are not necessarily the continents themselves The plates are not necessarily the continents themselves. Some are continents plus ocean floors (Indian plate). Some are all ocean floor (Nasca plate).

All of the plates together form the Lithosphere All of the plates together form the Lithosphere. The lithosphere is the portion of the Earth that undergoes tectonic activity. It is made up of the crust and a small part of the upper mantle.

The semisolid part of the mantle over which the plates slide is called the Aesthenosphere.

One of the largest divisions between plates is the Mid-Atlantic Ridge which separates the North American Plate from the Eurasian Plate and the South American Plate from the African Plate.

Collisions between plates cause (1) mountain ranges (like the Himalayas) or (2) subduction zones where one plate slides under the other, ultimately to be destroyed. This is responsible for most deep ocean trenches.

Not all plates collide, some “shear” past each other (San Andreas Fault). Sudden, jerky slippages of these faults cause earthquakes.

Some plates move apart (as in the Atlantic Ocean) Some plates move apart (as in the Atlantic Ocean). In these cases, the mantle material wells up forming ridges (Mid-Atlantic Ridge).

What moves the plates? Probably convection currents in the mantle.

Continental drift was proposed in 1912 by Alfred Wegener.

What evidence is there for continental drift?

1. Geographical evidence - the continents fit together. 2 1. Geographical evidence - the continents fit together. 2. Fossil evidence - Fossils of an extinct reptile are found only on the Brazilian coast and the west coast of Africa.

3. Ocean floor age - The ocean floor close to the Mid-Atlantic Ridge is young, farther away on either side gradually gets older.

4. Paleomagnetism - the Mid-Atlantic Ridge shows matching reversals of the Earth’s magnetic field on either side of the ridge.