Earth’s Interior Structure

Layers of the Earth Crust Mantle Outer Core Inner Core

Layers of the Earth Crust: The outermost layer of the Earth is the crust. This comprises the continents and ocean basins. The crust has a variable thickness, being 35-70 km thick in the continents and 5-10 km thick in the ocean basins.

Layers of the Earth Mantle: The next layer is the mantle. It is about 2900 km thick, and is separated into the upper and lower mantle. Large convective cells in the mantle circulate heat and drive plate tectonic processes.

Layers of the Earth Outer Core & Inner Core: The last layer is the core, which is separated into the liquid outer core and the solid inner core. The outer core is 2300 km thick and the inner core is 1200 km thick. Both the outer core and the inner core are composed of iron-nickel.

Layers of the Earth Asthenosphere & Lithosphere The topmost layer is the lithosphere, which is comprised of the crust and solid portion of the upper mantle. The lithosphere is divided into many plates that move in relation to each other due to tectonic forces. The lithosphere essentially floats atop a semi-liquid layer known as the asthenosphere. This layer allows the solid lithosphere to move around since the asthenosphere is much weaker than the lithosphere.

Lithosphere Uppermost layer Crust and upper mantle Cooler, moves as a rigid block

Lithosphere Broken into plates that move due to convection currents

Asthenosphere Molten rock with fluid qualities; flows very slowly, like stiff liquid Contains minerals such as magnesium, silicon oxides, garnets & olivine.

Convection Currents The force responsible for plate movement is convection.

Density Density- the mass per unit volume of material or substance. -Refers to how concentrated the mass (atoms and molecules) in an object or material is. -Less dense materials tend to rise upward and “float” on more dense material.

Density Rocks in the Earth’s crust are less dense than the underlying mantle. The crust “floats” on the more dense interior material. In other words, the lithosphere “floats” on the asthenosphere.

Convection Currents Temperature affects the density of materials. As rocks in the interior of the Earth are heated enough, their density decreases. The less dense rock rises slowly over time. The most likely source of the Earth’s internal heat is the decay of radioactive elements in the core.

Convection Currents The transfer of heat from Earth’s interior to its surface drives the movements of the Earth’s crust and mantle. The Earth can be thought of as a massive heat engine. Convection currents in Earth’s mantle occur because material is heated (becoming less dense) at the core mantle boundary. It rises upward, spreads out horizontally, cools (becoming more dense) and sinks back into the interior.

Convection Currents Material rises (density decrease) to the surface at places where lithospheric plates spread apart from one another. Material sinks (density increase) back into the Earth where plates converge. Thermal convection currents are like a conveyor belt, moving the lithospheric plates. These extremely slow-moving convection cells provide the driving force that moves the lithospheric plates.