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Earth’s Structure
Section 22.1
Science of Geology
• Geology- Study of planet
Earth, including its
composition and
structure.
• Scientists who study Earth
and processes that have
shaped Earth over time
are called geologists.
Science of Geology (Cont.)
• Modern science of geology began in
1700’s with James Hutton.
• Hutton was a Scottish physician and
farmer who made observations of
rocks and explained Earth was far
older than most people had
imagined.
• Also observed that some rocks came
from particles from older rocks, thus
realizing that Earth changed gradually
over time.
Science of Geology (cont.)
• Hutton developed the
principle of uniformitarianism,
an idea that the geologic
processes that operate today
also operated in the past.
• Dramatic features such as
mountains and canyons are
the result of geologic process
that work very slowly over
long periods of time.
A Cross Section of Earth
• Earth’s surface and interior can
be compared to a hard-boiled
egg.
• Earth is divided into 3 main
layers:
1) Crust
2) Mantle
3) Core
• Layers are divided based on
material of each layer.
The Crust
• Rocky outer layer of the Earth
is the crust
• Thinner compared to other
layers
• Most of crust is made of
silicates, rocks made of
compounds of silicon and
oxygen. Often contain metals
such as aluminum, iron, or
calcium.
The Crust (cont.)
• 2 different types of crust:
continental crust and
oceanic crust.
• Continental- Rock that
makes up continents,
consists mainly of less-dense
rocks such as granite.
• Averages 40 km in thickness,
although ranges about 8 to
75 km
The Crust (cont.)
• Oceanic Crust- composed
of mostly dense rocks like
basalt.
• Oceanic Crust is about 7
km thick on average, and
it much thinner than
continental crust
The Mantle
• Beneath the crust is the mantle, a thick
layer of hot but solid rock.
• Mantle extends about 2850 km from
beneath the crust to the top of the core.
• Pressure and temperature increase
tremendously the deeper you go into
the mantle.
• Mantle is composed mainly of silicates,
and is rich in iron and magnesium.
The Mantle (cont.)
• Geologists divide mantle into 3 layers
based on physical properties of rock:
1) Lithosphere
2) Asthenosphere
3) Mesosphere
• Lithosphere- Layer of relatively cool, rigid
rock that includes the uppermost part of
the mantle as well as the Earth’s crust.
• Lithosphere measures about 100 km,
although it is thicker below the
continents and thinner beneath the
oceans.
The Mantle (cont.)
• Asthenosphere- Layer of
softer, weaker rock that
can flow slowly
• Mesosphere- Lower part
of the mantle; stiffer rock
of mesosphere extends all
the way down to the
upper surface of Earth’s
core.
The Core
• Beneath mantle is the core; a
large sphere of metal that
occupies Earth’s center.
• Scientists think that core is
composed mostly of iron,
with lesser amounts of nickel
and some lighter elements.
• Within the core, pressure
increases greatly with depth.
The Core (cont.)
• At Earth’s center, pressure is
estimated to be 3.6 million times
the pressure of Earth’s surface!
• Temperature at center of Earth is
estimated to be about 5500
degrees Celsius (nearly temp. of
sun’s surface)
• Core is divided into 2 parts:
1) Outer Core
2) Inner Core
The Core (cont.)
• Outer Core- High temperatures
keep the meta liquid.
• Because of Earth’s rotation,
flowing iron of the outer core
produces an electric current
and creates Earth’s magnetic
field.
• Inner Core- Very high pressure
is a more important factor than
temperature. Inner core is solid.