Structure of the Earth

Earth’s Structure  The Earth is made up of several layers with distinct properties:  Crust = outer layer  Mantle = middle layer  Core = inner layer

Earth’s Structure  The structure of the Earth is measured indirectly using data from earthqukes  We know how seismic waves move through different materials  Much of the evidence comes from shadow zones where no P or S waves are seen

The Crust  The crust is not even around the whole Earth  The crust is thinner under the oceans and thicker under the continents  Oceanic crust is made up of dense rocks and is from 5 to 8 km thick  Continental crust is made up of lighter rocks and is from 10 to 70 km thick

The Crust  Because oceanic crust is much denser than continental crust = ocean plates are subducted in plate tectonics  The boundary between the crust and the mantle is the Mohorovičić discontinuity (Moho)

The Mantle  The mantle is largely solid rock with localized chambers of melted rock in the upper mantle = magma  The rock in the mantle is thought to be made up of rock with olivine and pyroxene, and lacking feldspar  The uppermost portion of the mantle and the crust make up the lithosphere (70 – 250 km thick)

The Mantle  The asthenosphere is the part of the mantle up to 200 km deep where seismic waves travel more slowly  This layer is thought to behave as a plastic material (like silly putty) because the rocks are close to their melting point  The asthenosphere is likely the source of magma since its rock is close to melting

The Core  The core is made of metals (mostly iron)  The core has two parts:  Liquid outer core  Solid inner core  Currents in the liquid part of the core create Earth’s magnetic field