Start Dating looking for examples

Dating looking for examples

Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence.

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.

The same margin of error applies for younger fossiliferous rocks, making absolute dating comparable in precision to that attained using fossils.

To achieve this precision, geochronologists have had to develop the ability to isolate certain high-quality minerals that can be shown to have remained closed to migration of the radioactive parent atoms they contain and the daughter atoms formed by radioactive decay over billions of years of geologic time.

It is only by correlations that the conditions on different parts of Earth at any particular stage in its history can be deduced.

In addition, because sediment deposition is not continuous and much rock material has been removed by erosion, the fossil record from many localities has to be integrated before a complete picture of the evolution of life on Earth can be assembled.

This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.

For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.

In addition, they have had to develop special techniques with which to dissolve these highly refractory minerals without contaminating the small amount (about one-billionth of a gram) of contained lead and uranium on which the age must be calculated.

Since parent uranium atoms change into daughter atoms with time at a known rate, their relative abundance leads directly to the absolute age of the host mineral.

Similarly, in geologic studies, vast quantities of information from widely spaced outcrops have to be integrated.