Download Earth`s Interior Key Concept Summaries 8.1 How Do Geologists

Earth’s Interior
Key Concept Summaries 8.1
How Do Geologists Learn About Earth’s Interior?
Processes that affect Earth’s surface are
often a result of what’s going on
inside Earth. Geologists have used two
main types of evidence to learn about
Earth’s interior: direct evidence from
rock samples and indirect evidence
from seismic waves.
Geologists have studied rock
samples that were taken from holes
drilled up to 12.3 kilometers deep.
They also study rocks from volcanoes
that originated around 100 kilometers
under the surface. These rocks give
geologists clues about Earth’s
structure and conditions deep inside
Earth.
Geologists also use an indirect
method of studying Earth’s interior.
When earthquakes occur, geologists
can study their seismic waves.
Seismic waves are vibrations that carry
the energy released during an
earthquake. The speed and paths of
seismic waves give geologists clues
about the structure of the planet.
What Are the Features of Earth’s Crust, Mantle, and Core?
The three main layers of Earth are the
crust, the mantle, and the core. These
layers vary greatly in size, composition,
temperature, and pressure. The
deeper inside Earth, the greater the
mass of the rock is that is pressing
down from above. Pressure results
from a force pressing on an area. The
deeper down inside Earth, the greater
the pressure. Pressure inside Earth
increases much like pressure in a
swimming pool increases at greater
depths. The temperature inside Earth
increases as depth increases.
The surface of Earth is known as
the crust, the layer of rock that forms
Earth’s outer skin. The crust is a layer
of solid rock that includes both dry
land and the ocean floor. About 40
kilometers beneath dry land, the rock
in Earth’s interior changes. The rock
below the boundary is the solid
material of the mantle, a layer of hot
rock. The mantle is made of rock that
is very hot, but solid. Scientists divide
the mantle into layers based on the
physical characteristics of those layers.
Overall, the mantle is nearly 3,000
kilometers thick. The uppermost part
of the mantle is brittle rock, like the
rock of the crust, so geologists often
group the crust and uppermost mantle
into a single layer called the
lithosphere. Below the lithosphere, the
material is a softer, solid layer called
the asthenosphere. Below the mantle
lies Earth’s core. The core is made
mostly of the metals iron and nickel. It
consists of two parts—a liquid outer
core and a solid inner core. The outer
core is a layer of molten metal
surrounding the inner core. Despite
enormous pressure, the outer core is
liquid. The inner core is a dense ball
of solid metal.
How Does Convection Occur in Earth’s Mantle?
The flow that transfers heat within a fluid is
called a convection current. Heating
and cooling of a fluid, changes in the
fluid’s density, and the force of gravity
combine to set convection currents in
motion. Inside Earth, large amounts of
heat are transferred by convection
currents within the core and mantle.
Heat from the core and the mantle
itself causes convection currents in the
mantle.
Over millions of years, the great
heat and pressure in the mantle have
caused solid mantle rock to warm and
flow very slowly. Many geologists
think that plumes of mantle rock rise
slowly from the bottom of the mantle
toward the top. The hot rock
eventually cools and sinks back
through the mantle. Over and over,
the cycle of rising and sinking
takes place.
Earth’s Interior
Review and Reinforce 8.1
Understanding Main Ideas
1. What two types of evidence do geologists use to learn about Earth’s interior?
_____________________________________________________________________
___________________________________________________________________
2. Name the three main layers of Earth.
___________________________________________________________________
3. The flow that transfers heat within a fluid is called a _________________________
_____________________. The heating and cooling of the fluid, changes in the
fluid’s density, and the force of gravity combine to cause convection currents.
4. What causes convection currents in Earth’s mantle?
_______________ from Earth’s core and mantle causes convection currents in Earth’s
mantle.
Building Vocabulary
If the statement is true, write true. If the statement is false, change the underlined
word or words to make the statement true.
5. ______________________ Convection currents give geologists clues about the
structure of Earth.
6. ______________________ The flow that transfers heat within a fluid is called a
convection current.
7. ______________________ Geologists often group the crust and uppermost mantle
into a single layer called the mesosphere.
8. ______________________ Scientists think that movements in the liquid outer core
create Earth’s seismic waves.
9. ______________________ Density is a measure of how much heat there is in a given
volume of a substance.