It is conceptually important that each rock has an origin in concepts of place, time, and physical and chemical conditions. These changes may be rapid (such as a volcanic explosion) or gradual, taking place over millions or billions of years, and involving movement over great distances, both at the surface or to deep within the Earth's crust below us.

The science of geology is founded on basic principles that are useful for making observations about the world around us.

This chapter presents a mix of information that is essential (fundamental) to all following chapters.

Everything around us is made of chemical compounds that have testable and identifying characteristics, allowing them to be classified, and their age determined.

This also applies to rocks, minerals, and derivative materials (such as sediments and soil).

I this case, the isotope is considered a radioactive form of an element.

Many elements have both stable and radioactive isotopes.

Rock form in a variety of geologic setting ranging from locations on or near the earth surface, deep underground, or even in outer space.

Most of the rocks we see on the surface of the planet formed by processes that happened long ago, but we can see these processes actively taking place in many places.

In "nature,"here are at least 254 stable isotopes that have never been observed to decay.