Glossary

A B C D E F G H I J L M N O P Q R S T U W
  • natural gas

    Hydrocarbons that exist as a gas or vapor at ordinary pressures and temperatures. Methane is the most important, but ethane, propane, and others may be present.

  • Neogene Period

    The interval of geologic time between 23 million and 2.6 million years ago.