Earth’s Interior
The Zones of Earth’s
Interior
Much of our knowledge of
the Earth’s interior comes
from the study of
earthquake (seismic)
waves.
Seismic waves seem to
change speed, direction
or disappear as they pass
through the Earth.
These changes suggest
that different zones of the
Earth exist due to
differences in states of
matter and/or density.
The zones of the Earth
include: the crust,
mantle, outer core and
inner core.
The Crust
The crust and
upper part of the
mantle are known
as the lithosphere.
The outermost portion of the Earth is known as
the crust.
The crust includes the solid bedrock upon
which we live, as well as, the soil and
weathered/eroded sediments from bedrock.
Two types of crust exist: continental crust and
oceanic crust. Continental crust makes up the
large continents that exist. It is thicker and
made up of largely light-colored, less dense
granitic rock.
Oceanic crust makes up the crust under the
oceans. It is thinner and made up of largely
dark-colored, more dense basaltic rock.
The crust is broken into large pieces called
plates.
The Mantle
The largest portion of the Earth is
known as the mantle. The mantle is
located beneath the crust.
The mantle is composed of many sublayers. Just below the crust is the
Moho – a thin interface between the
crust and mantle. Just below the Moho
is the Upper Mantle – a very dense
section of rock. These layers along
with the crust make up the lithosphere.
Another portion of the upper mantle is
known as the asthenosphere. The
asthenosphere is believed to be
“plastic-like” or partially molten.
Convection currents within the
asthenosphere allow the crustal plates
to move.
The Lower Mantle (stiffer mantle) is
located below the asthenosphere and
is more rigid .
The Outer
Core
The Outer Core of the Earth is located
beneath the mantle.
The dimensions of the outer core have
been determined by the behavior of
seismic waves that pass through it.
Some seismic waves slow down and
are refracted when they move through
the outer core (P-waves). Other
seismic waves are absorbed when
they pass through the outer core (Swaves).
Due to these observations, it is
theorized that the outer core is liquid.
It is theorized that the outer core is
composed of iron and nickel.
The Inner
Core
The Inner Core is located beneath the outer core.
The inner core is believed to be a solid due to tremendous pressure
surrounding it. Some seismic waves increase in velocity when passing
through the inner core. The inner core has the highest density of all
zones within the Earth.
It is theorized that the inner core is composed of iron and nickel.