Geologic age dating sequence
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.An unconformity is a buried erosional surface or non-depositional surface, a contact between the rocks below and the layer of stratified rock above that is missing a significantly large interval of geologic time.For example, deep in the Grand Canyon in Arizona, there are places where a layer of rock of Devonian age is right on top of a layer of rock of Cambrian age.You may have already completed introductory laboratory studies of igneous, sedimentary, and metamorphic rocks.If so, you have already practiced interpreting details of earth's history from the evidence contained in rocks.The idea of uniformitarianism is that the laws and principles that nature follows in today's world, such as gravity, also applied in the geologic past; in other words, "the present is the key to the past." The idea of uniformitarianisms is commonly misinterpreted in two different ways.The first incorrect interpretation is that it states that only slow changes occur on earth, the second misinterpretation is that it states that catalclysmic events cannot have happened in the past.
Because these units are used according to the rules of the metric system, the M in Ma and the G in Ga must be capitalized, and the k in ka must not be capitalized.
Relative geologic age is established, based on such evidence as the order in which layers of sediment are stacked, with the younger layer originally on top.
By using the principles of relative geologic age, the sequence of geologic events -- what happened first, what happened next, what happened last -- can be established.
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.