Glossary Starting with the letter: R


The spontaneous emission of energetic particles and/or radiation (including alpha particles, nucleons, electrons, and gamma rays) from either unstable atomic nuclei or as the consequence of a nuclear reaction.

Radiocarbon Dating

A dating method used to quantitatively measure the age of organic matter (such as bone, shell, or wood). The method can by applied to materials formed within the last 50,000 years or so.

Radiometric Dating

Determining the absolute age of rocks by measuring the decay of naturally occurring radioactive isotopes like carbon-14 or long-life isotopes of potassium, thorium, and uranium.


A fine-grained volcanic igneous rock usually light in color. Rhyolites commonly contain high amounts of silica, and low amounts of iron and magenesium. The fine-grained nature is a result of rapid cooling at the surface of Earth.

Richter Scale

An exponential scale ranging from 1 to 9 that measures the amount of energy released during an earthquake.

Ring of Fire

The name of the extensive area of volcanic and seismic activity that roughly coincides with the borders of the Pacific Ocean.


Any naturally formed aggregate of one or more minerals, such as granite, shale, or marble.


The free falling of detached bodies of bedrock from a cliff or steep slope.