The time units used by scientists to divide Earth's history are part of the

Geologic time scale

In the question "The time units used by scientists to divide Earth's history are part of the" the correct answer is the Geological Time Scale (GTS). The geological time scale (GTS) is a system of chronological dating that relates geological divisions to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history.