Glossary

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

    The interval of geologic time between 33.9 million and 23 million years ago.

  • Ordovician Period

    The interval of geologic time between 485 million and 443 million years ago.

  • organic

    Made from or derived from living matter. Coal is made from plants, which are organic.