Angular unconformity – tilted rocks are overlain by flat-lying rocks b. William Smith (late1700s–early 1800s) noted that sedimentary strata in widely separated areas could be identified and correlated by their distinctive fossil content 2.
Disconformity – strata on either side are parallel c. Principle of fossil succession – fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content a.
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.
Geologist are often trying to learn more about Earth and its history.
From the beginning of this course, we have stated that the Earth is about 4.6 billion years old.
How do we know this and how do we know the ages of other events in Earth history?
Crosscutting Relations are those where one rock literally cuts across another, such as for example when igneous dikes and sills are emplaced in fractures within a pile of sedimentary rocks (see picture at left).
Radiometric dating is a complex procedure that requires precise measurement 2.
Geologists analyze geologic time in two different ways: in terms of relative geologic age, and in terms of absolute (or numeric) geologic age.
The combination of these two types of geologic ages makes a complete record of earth's geologic history in terms of the order of events and in terms of how many years ago each event occurred.
Principles of Stratigraphy Stratigraphy is the study of strata (sedimentary layers) in the Earth's crust.
Geologist in the 1800s worked out 7 basic principles of stratigraphy that allowed them, and now us, to work out the relative ages of rocks.