September 16, 2013
I. Earth’s Interior
A. Exploring Inside Earth—throughout history, Earth’s surface has been lifted up, pushed
down, bent and broken.
1. Geologists have used 2 types of evidence to learn about Earth’s interior. They
use direct evidence from rocks and indirect evidence from seismic waves.
a. Rock samples from holes as deep as 12km (7.45 miles). These rocks can
tell us about the conditions inside of Earth.
b. Seismic waves created by Earthquakes move through the inside of Earth
in different paths and at different speeds depending on the material they are
moving through.
B. A Journey to the Center of Earth
1. The three main layers of Earth are crust, mantle, and core. They vary greatly in
size, composition, temperature, and pressure.
a. Temperature—as you dig deeper into Earth, the temp. continues to rise.
The heat is leftover from the formation of Earth, and from the breakdown of
radioactive elements.
b. Pressure—as you dig deeper, the weight of the rock above you creates
more and more pressure (like a swimming pool).
C. The Crust—the layer of rock that forms the Earth’s outer skin.
1. The crust is made up of the dry rock that makes up continents, and also the rock
at the ocean floor.
2. The crust is extremely thin (5-70km) compared to the other layers.
a. The thickest parts are under large mountains (up to 70 km thick).
b. The thinnest pars are at the ocean floor.
3. Oceanic Crust vs. Continental Crust
a. Oceanic crust is thin and dense. It is mostly made of basalt.
b. Continental crust is thick and low density. It is mostly made of granite.
September 16, 2013
D. The Mantle—the second layer of Earth made of very hot, solid material. The mantle is
nearly 3000km (1864 miles) thick.
E. Core—the innermost layer of Earth made up mostly of iron and nickel. It is about
3486 km (2166 miles) in thickness.
1. Movements in Earth’s liquid outer core create a magnetic field. This is why as
compass points north.
F. Compositional vs. Physical Layers
1. The 3 layers listed above (crust, mantle, and core) are divided based on their
composition, or what they are made up of.
2. We also can divide the layers based on their physical properties, or how they
behave.
a. Lithosphere—outermost rigid layer of Earth that is composed of the crust
and upper mantle. It is about 100 km (62 miles) thick. This layer is broken
into tectonic plates.
b. Asthenosphere—soft layer of the mantle on which the lithosphere moves.
This layer is softer, but still solid.
c. Mesosphere—The lowest layer of the mantle. It is hotter and under more
pressure than the previous layers.
d. Outer Core—The extremely hot, liquid layer made of nickel and iron. It
is under enormous pressure.
e. Inner Core—A dense ball of solid metal. The temp. is hot enough for it to
be a liquid, but the pressure is so great the atoms cannot spread to become a
liquid.