The Earth -- What is it?

The Earth has a radius of about 6371 km, although it is about 22 km larger at equator than at poles.


Internal Structure of the Earth:

Density, (mass/volume), Temperature, and Pressure increase with depth in the Earth.

Compositional Layering

Crust - variable thickness and composition
Continental 10 - 50 km thick

Oceanic 8 - 10 km thick

Mantle - 3488 km thick, made up of a rock called peridotite

Core - 2883 km radius, made up of Iron (Fe) and small amount of Nickel (Ni)




Layers of Differing Physical Properties

Lithosphere - about 100 km thick (deeper beneath continents)


Asthenosphere - about 250 km thick to depth of 350 km - solid rock, but soft and flows easily.


Mesosphere - about 2500 km thick, solid rock, but still capable of flowing.


Outer Core - 2250 km thick, Fe and Ni, liquid


Inner core - 1230 km radius, Fe and Ni, solid

All of the above is known from the way seismic (earthquake waves) pass through the Earth as we will discuss later in the course.

Surface Features of the Earth

Oceans cover 71 % of Earth's surface -- average depth 3.7 km. Land covers remaining surface with average of 0.8 km above sea level




Ocean Basins

Continental Shelf, Slope, and rise
Abyssal Plains
Oceanic ridges
Oceanic Trenches