1. Earth has several layers.
Unit A Section 1.1

2. What is the age of the Earth?
Scientists estimate the age of the Earth to be approximately 4.6 billion years old.
They theorize that Earth began as a spinning mass of rock and dust.
Explosions from comets and asteroids, along with intense gravity and pressure produced the heat to melt materials inside the Earth.

3. Temperature/Thickness
Layer
Composition
Temperature/Thickness
Inner Core
Solid Metals
7,000- 8,000 ºC
2,400 km diameter
Outer Core
Liquid Metals
4,400- 6,100 ºC
2,300 km thick
Mantle
Heated Rock
870- 4,400 ºC
2,900 km thick
Crust
Cooler Rock
0-700 ºC
6-7 km thick
1- continental crust-thicker
2- oceanic crust- thinner

5. Earth’s crust + top layer mantle=lithosphere
Lithosphere sits atop soft, hot rock layer (magma) in the mantle= asthenosphere.
The lithosphere is made up of many plates- slabs of rock called tectonic plates, which fit together like a puzzle.

7. Discovery of Earth’s layers and tectonic plates led to new discoveries:
- continental drift
- sea floor spreading