The Earth’s Interior
Notes
No one has been to the center of the Earth. Scientists know about the structure
of the Earth’s interior because they have studied vibrations (seismic waves)
generated by earthquakes.
I. Earth’s Layers by Composition (layers made of different mixtures of
elements)

Crust
o
o
o
o
o
o
o
Outermost layer
5-30 kilometers (km) thick
thinnest layer
We live on this layer
Makes up less than 1% of Earth’s mass
We know more about this layer than any other
Two types of crust
 Continental Crust
 Made up of mostly granite
 Averages 30 km thick
 Thickest under mountains
 Oceanic Crust
 Made up of mostly basalt
 Averages 5-8 km thick
 More dense than Continental Crust
o Oceanic Crust slides below Continental Crust
 A subduction zone is where this occurs
 See diagram of a subduction zone below


Mantle
o Dense layer made up of hot, semi-solid rock
o Extremely thick (the thickest layer)
o Contains most of Earth’s mass
o No one has ever seen it
o Tectonic forces (convection currents) push the mantle up to the
surface
 Convection currents – warm material rises because it is
less dense, cooler material sinks because it is more
dense
o Ocean floor volcanoes are the best place to look at the material
in the mantle
 The composition shows large amounts of iron and
magnesium which is called olivine
Core
o Mostly iron with small amounts of nickel and possible small
amounts of sulfur and oxygen
o Begins at the bottoms of the mantle to the center of the Earth
o Earth’s core is similar to the diameter of Mars
o Separated into the Outer Core and Inner Core
II. Earth’s Layers by Physical Properties (temperature, density, and ability
to flow)
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Lithosphere
o Outermost, rigid “rock”
o Two parts of the lithosphere
 Crust
 Upper part of the mantle
o Divided into tectonic plates
Asthenosphere (weak sphere)
o Soft layer on which the pieces of lithosphere (tectonic plates)
move
o Solid rock that flows like “silly putty”, plasticity
Mesosphere/mantle
o Middle sphere
o Strong lower part of the mantle that extends from the bottom of
the asthenosphere to the Earth’s core
Outer Core
o Believed to be mostly liquid iron and some nickel
o Because it is iron, it is very dense
o High temperatures and pressure
o Between the mesosphere and the inner core
o Movement of the liquid metal in the outer core is responsible for
the Earth’s electromagnetic field
Inner Core
o Believed to be solid iron and nickel because the 5000 km of
rock above it exert enough pressure to change the liquid rock
into a solid
o The solid, inner core spins in the same direction as Earth spins,
but more quickly
o As hot as the Sun’s surface
o Very dense
o Approximately 6400 km beneath the surface