Dating of rocks and geologic events

Earth is about 4. Geologists divide this age into major and minor units of time that describe the kinds of geological processes and life forms that existed in them. Earth's geologic record was formed by constant change, just like those that occur routinely today. Though some events were catastrophic, much of Earth's geology was influenced by normal weather, erosion, and other processes spread over very long geologic ages.

Dating , in geology , determining a chronology or calendar of events in the history of Earth , using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments. To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques. These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events. Radiometric dating and certain other approaches are used to provide absolute chronologies in terms of years before the present. The two approaches are often complementary, as when a sequence of occurrences in one context can be correlated with an absolute chronlogy elsewhere. Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.

Using relative and radiometric dating methods, geologists are able to answer the question: how old is this fossil? Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free. As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils. A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved. However, by itself a fossil has little meaning unless it is placed within some context.

Geologists count back more than 4 billion years to the oldest Earth materials. Have you ever tried to count to a million? Counting once per second easy at the start, but tough when you reach the hundred-thousand mark , 24 hours per day, seven days per week no weekends off , it would take you 11 days, 14 hours to count to one million! There are a thousand millions in a billion, so counting to a billion would take you approximately 32 years.