Download Inner Core - Net Start Class

CRUST
The brittle, rocky outer layer of the Earth is called the crust. It is much thinner than the other
layers, like the shell of a hard-cooked egg. It is the least dense layer. It is made mostly of
elements of low mass, such as silicon and oxygen.
Crustal rocks are under oceans and on land. The crust under oceans is called oceanic crust. It is
made of dense rocks that contain iron and magnesium. The crust on land is called continental
crust. It is about four times thinker than oceanic crust. Continental crust is thickets under tall
mountains.
There is a distinct boundary between the crust and the layer beneath it. When earthquakes
cross this boundary, they speed up. This indicates that the lower layer is denser that the crust.
MANTLE
Earth’s mantle is immediately below the crust. The mantle is the thick middle layer in the solid
part of Earth. It contains more iron and magnesium than oceanic crust does. This makes it
denser than either type of crust. Like the crust, the mantle is made of rock. The iron-rich rocks
of this layer are peridotite and eclogite. Scientists group the mantle into four layers according
to the way rocks react when forces push or pull on them.
Uppermost Mantle
The rocks in the uppermost layer of the mantle are brittle and rigid, like rocks in the crust.
Because of this, scientists group the crust and the uppermost mantle into a rigid layer called the
lithosphere.
ASTHENOSPHERE
Below the lithosphere, rocks are so hot that tiny bits melt. When this happens, the rocks are no
longer brittle. They begin to flow. Scientists use the term “plastic” to describe rocks that flow in
this way. The plastic layer within the mantle is called the asthenosphere. The word plastic refers
to materials that are soft enough to flow. The asthenosphere flows very slowly. Even if it were
possible to visit the mantle, you could never see this flow. Rocks in the asthenosphere move
about as slowly as your fingernails grow.
UPPER MANTLE AND LOWER MANTLE
The rock below the asthenosphere is solid, but it is hotter than the rock in the asthenosphere.
How can this be? The pressure at this depth is so great that no melting occurs. While increased
temperature tends to melt rock, high pressure tends to prevent melting. High pressure
squeezes the rock into a solid. This solid rock of the upper mantle and the lower mantle forms
the largest layer of Earth.
OUTER CORE
The outer core is a liquid layer that is makes up part of Earth’s dense metallic center. If you
imagine Earth as a hard-cooked egg, the core is the yolk. If Earth’s crust and mantel are made of
rock why is the core made of metal? Recall that in Earth’s early history, the planet was much
hotter than it is now. Earth materials flowed, like they do in the asthenosphere today.
Scientists do not know how much of Earth melted, but they do know that it was soft enough for
gravity to pull the densest material down to the center. This dense material is metal. It is mostly
iron with small amounts of nickel and other elements. The mantle and core are made of
different materials, and have different melting temperatures. Just like in the asthenosphere,
the effects of temperature outweigh the effects of pressure in the outer core.
INNER CORE
The inner core is a dense ball of solid iron crystals. The pressure in the center of Earth is so high
that even at temperatures of about 6,000°C, the iron is in a solid state. Because the outer core
is liquid, it is not rigidly attached to the inner core. The inner core spins a little faster than the
rest of the Earth.