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Earth’s Interior
Structure
Layers of the Earth
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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.