Officially, the current epoch is called the Holocene, which began 11,700 years ago after the last major ice age. The study of this correlation is called stratigraphy. From examining these fossils, scientists know that certain organisms are characteristic of certain parts of the geologic record. These units are classified based on Earth’s rock layers, or strata, and the fossils found within them. These divisions, in descending length of time, are called eons, eras, periods, epochs, and ages. Earth’s history is divided into a hierarchical series of smaller chunks of time, referred to as the geologic time scale.
