Much of the most detailed and precise information that geologists have gleaned of earth's history comes from a branch of geology known as stratigraphy.
Stratigraphy studies stratified rocks, - layered rocks, in other words, which are either sedimentary or volcanic - establishes their age sequence based on principles of relative geologic age, and reconstructs, from the evidence in the rocks and from their field relations as depicted on maps and cross-sections, the geologic history that they represent.
This principle was based on applying other methods of determining which rocks are older and which rocks are younger, which verifies that there is indeed a faunal (or fossil, if you prefer) succession that occurs in the same order in the rock layers everywhere on earth.
Charles Lyell developed a key idea known as uniformitarianism, which also underlies the geological study of earth's history.
Geologic time covers the whole sweep of earth's history, from how and when the earth first formed, to everything that has happened on, in, and to the planet since then, right up to now.
Geologists analyze geologic time in two different ways: in terms of relative geologic age, and in terms of absolute (or numeric) geologic age.
You may have already completed introductory laboratory studies of igneous, sedimentary, and metamorphic rocks.