Earth has several layers.Earth has several layers.

Unit A Section 1.1Unit A Section 1.1

What is the age of the Earth?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.

LayerComposition Temperature/Thickness

Inner Core Solid Metals 7,000- 8,000 ºC2,400 km diameter

Outer Core Liquid Metals 4,400- 6,100 ºC2,300 km thick

Mantle Heated Rock 870- 4,400 ºC2,900 km thick

Crust Cooler Rock 0-700 ºC6-7 km thick1- continental crust-thicker2- oceanic crust- thinner

Earth’s crust + top layer mantle=lithosphereEarth’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.

Discovery of Earth’s layers and tectonic plates led to new discoveries:

- continental drift

- sea floor spreading