Notes: Layers of the Earth
Crust
Outer layer; covers the whole earth; varies in thickness from 5 to
60 Km. Together with the upper mantle, is part of a zone called
the lithosphere.
There are 2 kinds of crust: continental crust and oceanic crust.
Continental Crust
Exists under continents
Average thickness is 30-50 Km (thickest under mountains),
although it can be as thin as 10 Km in places
Chemical composition: rocks rich in calcium and aluminum
silicates
**Note: a silicate contains the molecule, SiO2
Common rock types: granite and rhyolite
Rocks are less dense, lighter in color than oceanic crust
Oceanic Crust
Exists under oceans
Average thickness is 7 Km
Chemical composition: rocks rich in iron and magnesium silicates
Common rock types: basalt, obsidian, gabbro
Rocks are more dense, darker in color than continental crust
Mantle (Chemical Composition: iron & magnesium silicates)
Lies underneath the crust
2900 Km thick
The lithosphere is a zone made of the upper mantle and entire
crust. It is made of cool, hard rock.
Most (but not the very upper part) of the mantle is plastic rock: is
both solid and molten at the same time. This zone is called the
asthenosphere.
Underneath the asthenosphere is the mesosphere, which is solid.
