Notes on Basic Geology
Notes created & information organization based on the book:
The Dynamic Earth - an introduction to physical geology"
Brian Skinner & Stephen C. Porter   (further book information here)
also look at for additional resource information
Introduction - A First Look - Page 3

The Internal Structure of the Earth

As the earth grew in its early stages, it added mass from accretion. Eventually enough heavy elements were added and radioactive materials began to aid in the planet heating.

This internal heating provided the energy necessary to begin the migration of the internal elements and chemical compounds. The heavier elements, like iron and nickel sank to the center, and the lighter materials, silicon, potassium, sodium, and aluminium rose to the surface.

As the internal heating continued, gases (oxygen, water, nitrogen, and sulphur) were released from volcanoes and eventually created the atmosphere and the oceans. Oxygen combined with many of the lighter elements and formed SiO2 (silica) and other aluminium, and lighter-metal oxides. These were the building blocks of the crust.

The earths layers

At the center of the earth is a dense body called the CORE. It is a dense body composed mainly of dense metals including iron, nickel and other heavy elements.

The next layer out is the MANTLE, and is less dense than the core, but more dense than the crust. At the outside of the planet is the CRUST. It is the least dense.

1.) Crust

2.) Upper Mantle
3.) Lower Mantle

4.) Outer Core
5.) Inner Core

Rock Strength
Crust + 100 km
Upper Mantle

Upper Mantle -
top 100 km

Lower Mantle



This layer floats on the upper mantle and is the lightest and most rigid of the layers. Oceanic crust (5-8 km) is much thinner than continental crust (25 -70 km).
100 Km of Upper Mantle The first 100 km of mantle make up a stable zone for rocks that is less pliable and more rock like than the mantle below.

Upper Mantle -100 km

100 km - 350 km

This layer appears to have the same general chemistry as the lower mantle, but the combination of temperature and pressure produces a non-stable zone for rocks. It is far more pliable. "Asteno" means weak. This layer is easily deformed.

Lower Mantle

350 km - 2880 km

At these depths, pressure takes over from heating and once again forms a stable rock phase with good strength. "Meso" means middle. (Between the core and the surface)