Chapter 9

an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom

unit of geologic time that includes two or more periods

a unit of geologic time that is longer than an epoch but shorter than an era

a subdivision of geologic time that is longer than an age but shorter than a period

the process of change by which new species develop from preexisting species over time

the interval of time in the geologic time scale from earths formation to the beginning of the Paleozoic era from 4.6 billion to 542 million years ago

the geologic era that followed Precambrian time and that lasted from 542 million to 251  million years ago

an episode during which large numbers of species become extinct

the geologic era that lasted from 251 to 65.5 million years ago age of the reptiles

the current geologic era which began 65.5 million years ago also called the age of mammals