Geology is the scientific study of the Earth. It includes figuring out how the Earth was formed, interpreting what sort of things have happened throughout Earth's history, and analyzing how the Earth is structured. So, this includes rocks, minerals, volcanoes, earthquakes, plate tectonics, and fossils, among other things. I spent about 10 years studying this science in college and graduate school.

Earth History

Earthquakes

NASA's Visible Earth

Incredible images of the Earth, taken from space. Includes all sorts of close-ups too, as well as distance shots.

See what sand from around the world looks like under a microscope. Pick your sample to analyze from a world map.

United States Geologic Survey

This gets you to the home page of the USGS. This is the research group run by the US government to study all things geologic.

Volcanoes

As always, I can be reached at askmrc@earthlink.net.