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.
A unit of geologic time that includes two or more periods.
A unit of geologic time that is longer that 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.
Yhe geologic era that followed precambrian time and that lasted from 542 to 251million years ago.
Large numbers of species become extinct
The geologic era that lasted from 251 million to 65.5 million years ago also called the Ages of Reptiles
The current geologic era, from which began 65.5million years ago also called ages of Mammals.