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Earth Systems
6.E.2.1 Earth’s layers
Layers of the Earth
 The earth is composed of 4 main layers:
1. The crust
2. The mantle
3. The outer core
4. The inner core
 Layer Video
The Crust
 The earth’s crust is its outermost layer, and is
divided into two types:
1. 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.
2. 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:
1. Liquid outer core
2. 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 3.33.6 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.