What is stratigraphy dating

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They did not know how many thousands, millions, or billions of years ago the Cambrian period began, but they knew that it came after the Proterozoic Eon and before the Ordovician Period, and that the fossils unique to Cambrian rocks were younger than Proterozoic fossils and older than Ordovician ones.In the 20th century, radiometric methods of absolute age determination were developed.How would today's sediments appear to a geologist millions of years in the future examining outcrops of sedimentary rock that originated in our time?What would the geologist be able to deduce about the world we live in, based on what was left in the strata?Unconformities separate chapters in the geologic history of a given region.For instance, an orogenic episode (a long geologic episode of mountain building) may finally come to end and the eroded mountains may be buried beneath a new sequence of sediments.There are no sedimentary strata to record what happened during the intervening interval.

By the end of the 19th century, geologists had used these principles to put together an outline of the geological history of the world, and had defined and named the eons, eras, periods, and epochs of the geologic time scale.Relative dating does not provide actual numerical dates for the rocks.Fossils are important for working out the relative ages of sedimentary rocks.Another essential concept in stratigraphy is the unconformity.An unconformity is a surface upon which no new sediments were deposited for a long geologic interval.

These methods allow the ages of certain types of rocks and minerals to be quantified in terms of years.

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