Earth Systems 6.E.2.1 Earth’s layers

Layers of the Earth The earth is composed of 4 main layers: The crust The mantle The outer core The inner core Layer Video

The Crust The earth’s crust is its outermost layer, and is divided into two types: Continental crust: this forms the continents and extends to the continental shelves (shallow seas close to a continent’s coast). It is typically 20-30 miles thick. Oceanic crust: this is the outer layer of the earth under the seas past the continental shelf. It is typically 3-6 miles thick.

What’s the difference? Continental crust is made up of slightly less dense rocks than the oceanic crust.

The Mantle The mantle is the layer of the earth between the crust and the outer core. It has an average thickness of 1,793 miles. The mantle makes up about 84% of the earth’s volume. The mantle is more dense than the crust.

Mantle Structure The mantle is mostly solid, but flows in geological time where it behaves as a very slow-moving, thick fluid. It has two main parts and a transition zone. Upper mantle: 250 miles deep Transition zone: 250-410 miles deep Lower mantle: 410-1,793 miles deep

Lithosphere and Asthenosphere The lithosphere is solid outer section of the earth, including the crust and the rigid part of the upper mantle. It is 44-62 miles thick. The asthenosphere is a part of the upper mantle involved in plate tectonics. It is a highly viscous solid. The asthenosphere is 50-120 miles thick. Together, the lithosphere and asthenosphere make up the upper mantle.

The Core The core is composed of 2 parts: Liquid outer core Solid inner core Core Video

The Outer Core The outer core is a layer of fluid metal between the mantle and the inner core. It is mostly made up of iron and nickel. The outer core starts about 1,800 miles beneath earth’s surface and ends about 3,200 miles beneath the earth’s surface. This makes the outer core about 1,400 miles thick.

Outer Core Properties It is extremely hot: 7,280°F at the outer boundary, to 10,340°F at the outer core-inner core boundary. In comparison, a candle burns at about 2,600°F! Because of the heat, the metals are molten and flow like a thick liquid.

The Inner Core The inner core is Earth’s innermost layer. It is about 760 miles thick. It is estimated to be extremely hot- around 10,800°F! That is hotter than the surface of the sun!

Inner Core Properties Despite this heat, the pressure at the center of the earth squeezes the inner core into a solid ball. The pressure in the inner core is estimated to be 3.3- 3.6 million times atmospheric pressure at sea level. The inner core is mostly made up of nickel-iron alloy, but contains other heavy elements in trace amounts. The inner core is the most dense layer of the earth.

Review The earth has 4 layers: the crust, the mantle, the outer core, and the inner core. Pressure, density, and temperature all increase as you go deeper into the earth. Each layer has different chemical and mechanical properties.