Earth’s Composition

Formation of Layers of Earth

OBSERVATIONS:• The Earth is not uniform!• The layers generally become denser with

depth.THEORY:• Scientists think that Earth was once molten

and denser materials settled towards the core and low-density materials floated to the surface. (all due to gravity)

Layers of the Earth

Boundaries that mark density changes between layers are discontinuities.Ex: Mohorovicic discontinuity separates the crust from the mantle.

Project Mohole• 1958-1966• Attempt to dig to Mohorovicic Discontinuity

How do we know information about Earth’s interior?

• Scientists have studied seismic waves.• P-waves (primary) are longitudinal and can travel through

solids and liquids. They travel through liquids more slowly.• S-waves (secondary) are transverse and cannot travel through

liquids.

Elements Found in each Layer of Earth

• Core: Fe, Ni

• Mantle: O (44%), Mg (22%), Si (21%), Fe (6%)

• Crust: O (46%), Si (28%), Al (8%), Fe (5%)

• DENSITY TREND EXISTS FOR THE ELEMENTS