These radioactive isotopes are parent isotopes, which decay slowly to daughter isotopes, changing the rock’s isotopic character.
The rate at which the isotopes decay is in effect our "geological clock".
Consider a lake that dries out or somehow contains older sediments that are washed into it.
These sediments are deposited on top of younger sediments currently being deposited in the lake.
For example, archaeologists might date materials based upon relative depth of burial in a site.
The archaeologists record and analyze the changes in types and styles of human-made items from different levels according to the principle explained below.
Perhaps the most widely used evidence for the Theory of Evolution through Natural Selection is the fossil record.
The fossil record may be incomplete and may never fully completed, but there are still many clues to evolution and how it happens within the fossil record.
These techniques are often combined together to get the most detailed dating information from a rock sequence.
Methods of dating rocks Absolute dating involves determining a rock’s actual age as a number of years, whereas relative dating methods provide an estimate of the age of a rock by comparing it to rocks of a known age The Geological Time Scale has been created by combining both absolute and relative dating methods.
By measuring the amount of the parent and daughter isotopes in a crystal, and then applying the decay rate, the actual age in years since the rock crystallized can be calculated.
Check out this video on the Uranium – Lead dating method: Biostratigraphy is a relative dating method that correlates rock ages using the fossils contained within rock units.
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