the geologic time scale a. began when earth formed and ended when humans first appeared. b. began when life first appeared and still continues today. c. began when life first appeared and ended when humans first appeared. d. began when earth formed and still continues today.

The geologic time scale began when earth formed and still continues today. Geologists measure "geologic time" by starting at the Earth's surface and working their way down via younger surficial deposits and older rocks.A depiction of time based on Earth's rock record is called the geologic time scale, or GTS. It is a method of chronological dating that makes use of geochronology and chrono stratigraphy, which relate strata to time (scientific branch of geology that aims to determine the age of rocks).It is largely employed to explain the time and linkages of events in geologic history by Earth scientists, such as geologists, paleontologists, geophysicists, and geochemists. The study of rock strata, observation of their correlations, and identification of elements like lithologies, paleomagnetic characteristics, and fossils have all contributed to the development of the time scale.Learn more about Geology here:https://brainly.com/question/28369999#SPJ4