Geology Reference
In-Depth Information
Every system needs energy to fuel its processes. Systems on earth's surface
are fueled by heat energy from the sun, while other systems (particularly those in
the geosphere) are fueled by heat energy from deep within the earth.
Because earth is one giant system, geologists study not only the rock materials on earth
but also how rocks in the geosphere interact with the other spheres.
Examining Earth's Geosphere
Many geologists study portions of the earth that can be seen. However, some of the
most fascinating unanswered questions about the earth have to do with what is going on
inside — beneath the rocks we can see and touch at the surface.
Humans do not yet have technology advanced enough to dig more than about 12 kilo-
meters (about 7.5 miles) into the earth's crust. So how do scientists know anything
about the inside of the earth? They combine their observations of rocks on the surface
with knowledge gained from laboratory experiments of temperature and pressure on dif-
ferent materials. Doing so gives them a pretty solid basis on which to make inferences
about what occurs in places that can't be directly observed.
Defining earth's layers
One way scientists separate the layers of earth's geosphere is by
physical properties,
or
whether the layers are liquid or solid.
Because geologists cannot see inside the earth, they make observations about earth's
internal properties by proxy: by interpreting information from earthquake waves that
can be used to make inferences about the physical properties of earth's interior.
When earthquakes occur, they send out waves. Two types of seismic waves,
called
S waves
and
P waves,
are used by scientists to learn about the interior of
the earth
.
These seismic waves are recorded by instruments called
seismometers,
which are buried underground all over the planet. When an earthquake occurs,
the seismometer sends a signal from underground to a machine in a lab (a
seismo-
