The Structure of the Earth

Earth’s Layers are divided into three layers ***Add Earth’s Layers Composition picture *** Whole page Earth’s Layers are divided into three layers based on their composition. The composition is based on the compounds that make up each layer. ***a compound is a substance made up of two or more elements. The three compositional layers from least dense to most dense are : mantle Crust, Mantle, core Core crust

The composition of the Earth The Crust: *the outer most layer * 5-100 km thick is the thinnest layer of the Earth only 1% of its mass * there are two types of crust: continental crust is about 30-100 km oceanic crust is about 5 km thick * both are made mainly of the elements oxygen, silicon, and aluminum *oceanic crust is denser and has twice as much iron, calcium, and magnesium which form minerals that are denser ** insert picture of oceanic and continental crust

The composition of the Earth The Mantle: the layer of the Earth between the crust and the core Is thicker than the crust and contains most of the Earth’s mass 67% and is 2,900 km thick It is too thick to drill through but Scientists know about the composition based on observations on Earth’s surface from rock pushing on to the surface (ex: underground volcanoes) Scientists have drilled about 12km (7.5 mi) into the crust The mantle has more magnesium and less aluminum than the crust so it is denser.

The Mantle The Mantle is the largest layer of the Earth. The middle mantle is composed of very hot dense rock that flows like asphalt under a heavy weight. The movement of the middle mantle (asthenosphere) is the reason that the tectonic plates of the Earth move.

Convection Currents The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again… repeating this cycle over and over.

Convection Currents Hot rock deep within the Earth rises Cooler rock near the surface sinks These currents cause the middle mantle to flow

The Core The center part of the Earth below the mantle About 33% of Earth’s mass Mostly made of iron and contains small amounts of nickel

Earth’s Layers are also classified by: Physical Structure Lithosphere solid Asthenosphere Viscous (means “syrupy”) Mesosphere viscous Outer Core liquid Inner Core

The Earth’s Structure Mesosphere

Lithosphere litho- means “rock” Cool, stiff outer layer of the Earth Made up of two parts The crust The rigid upper layer of the mantle (asthenosphere) It is divided into pieces called tectonic plates

The Lithospheric Plates The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere.

Asthenosphere astheno- means “weak” A layer of the mantle on which the tectonic plates move Made of hot, solid rock that flows very slowly

The Asthenosphere The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy weight.

Mesosphere meso- means “middle” The lower part of the mantle Flows more slowly than the asthenosphere

The Outer Core The core of the Earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron.

The Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together. They are not able to move about like a liquid. They are forced to vibrate in place like a solid.

The Core Outer Core Inner Core About 2,240 km (1400mi) thick Made of liquid iron and nickel Inner Core 2,440km (1540 mi) in diameter A ball of solid iron and nickel due to intense pressure Very hot 6,000 C (11,000 F)

How do we know about Earth’s layers? Scientists have learned about the composition of the Earth’s layers by recording and analyzing the seismic waves that travel through the Earth during an earthquake (see textbook page398) Studying Volcanoes