• Geologists have only been able to drill to 3.8
• The center of the Earth is more than 6,000
Since Geologists cannot observe the Earth’s
interior directly, they must rely on indirect
• Seismic Waves are recorded and study how they
travel through the medium of the Earth.
•This information has shown that the Earth has
Crust: the layer of rock that
forms Earth’s outer skin.
• The crust includes rocks,
mountains, soil, and water.
• The outer rind of rock is
much thinner than what is
• The crust includes both dry land and the ocean floor.
• It is thinnest beneath the ocean and thickest under
•The crust can range from 5-40 kilometers.
•Oceanic crust is made up of basalt.
•Continental crust is made up of granite.
The mantle is a layer of hot rock that extends nearly 3,000
• The Lithosphere is the upper portion of the mantle and the
lower portion of the crust.
• It is approximately 100 kilometers deep and floats on top
of the Asthenosphere .
•The Asthenosphere is a soft layer of the mantle.
•This layer flows slowly.
•The Asthenosphere is approximately 350 kilometers deep.
•The Mesosphere is the solid lower part of the mantle
below the Asthenosphere .
Earth’s Magnetic Field
• Currents in the liquid outer core force
the solid inner core to spin. (planet
•The inner core spins slightly faster
than the rest of the planet.
•This movement creates the Earth’s
The theory that states that pieces
of Earth’s lithosphere are in
constant, slow motion, driven by
convection currents in the mantle.
• The theory of plate
tectonics explains the
subduction of Earth’s
Forces that causes Earth’s
plates to move.
• The plates of the lithosphere float on top of the
• Convection currents rise in the Asthenosphere and
spread out beneath the lithosphere.
• Convection current forces drag the overlying plates
along. The currents cool and sink deeper into the
• Scientists think that the downward movement may
provide the force that causes the subduction of plates
carrying oceanic crust.
Slab Push Hypothesis
• Magma rising along the mid oceanic
ridge exerts a force that pushes an oceanic
plate away from the ridge.
• The force of gravity causes plate
movement by pulling cooler, denser
oceanic plates down toward the mantle.
• Slab push and pull work together with
convection currents to move the plates.
The earth’s surface is
made up of about nine
large plates and several
• When divergent boundaries develop
on land, two of Earth’s plates slide
• A rift valley forms along the
• Ex. The Great Rift Valley in east
Africa is about 3,000 kilometers long.