Earth’s Interior and Plate Tectonics

Earth’s Composition: Not just solid rock Distinct layers Each layer has certain physical properties

3 Main Layers when dividing them by their composition Crust Mantle Core

Crust Outermost layer 5 – 100 km thick Thinnest layer High in Silicon and Oxygen (makes rocks called silicates) < 1% of Earth’s mass

Average thickness of 30 km Composition similar to granite Continental Crust Average thickness of 30 km Composition similar to granite

Average thickness from 5-8 km Composition similar to basalt Oceanic Crust Average thickness from 5-8 km Composition similar to basalt

Oceanic crust is more dense than Continental crust

Mantle Between crust and core Extremely thick and 66% (2/3) of Earth’s mass Large amounts of Calcium and Magnesium

33% (1/3) of Earth’s mass 2 separate layers Mostly Iron and Nickel The Core 33% (1/3) of Earth’s mass 2 separate layers Mostly Iron and Nickel

There are 5 layers when we divide them up by their physical properties Lithosphere Asthenosphere Mesosphere Outer Core Inner Core

Made of the Crust and Upper Mantle Rigid, solid, cool Lithosphere Made of the Crust and Upper Mantle Rigid, solid, cool About 150 km thick

Lithosphere is broken into tectonic plates

Asthenosphere Upper part of the mantle 1-5% liquid rock Flows like putty, or plastic (very viscous) Lithosphere (tectonic plates) slide around on the asthenosphere

Mesosphere The middle layer when dividing them up into 5 parts Same as the mantle About 1% liquid High viscosity Flows very slowly

Hot, but not as hot as the inner core Outer Core Liquid layer Hot, but not as hot as the inner core

Inner Core Solid and most dense layer 6,000o Celsius (hotter than Sun’s surface) So why is it solid?

Some plates contain both continental and oceanic crust

How do we know what the Earth’s interior looks like?

12.2 km into the earth Kola Pennisula, Russia 1984 Deepest hole drilled: 12.2 km into the earth Kola Pennisula, Russia 1984

Seismic Waves From earthquakes There are 3 different types Travel through earth’s layers Transmission depends on phase (density) of the layer

But why do tectonic plates move?

Convection Currents The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. The crust gets a free ride with these currents, like the cork in this illustration.

Dynamics of the mantle…