Absolute Dating

Relative and Absolute Dating There are two major ways to date geologic events: 1) Relative dating-how old a rock is compared to surrounding rocks 2) Absolute dating-actual number of years since the rock was formed

Absolute Dating Absolute dating can give you the exact age of a rock This is accomplished using radioactive dating A.K.A radiometric dating Based on the regular radioactive decay of certain elements

Radiometric Dating of Rocks 1896-1898 Radioactivity discovered by: Henri Becquerel and Marie and Pierre Curie.

Phenomenon of Radioactivity Some elements, such as uranium (U) and thorium (Th), are unstable: They decay spontaneously.

To estimate the age of a rock: P = amount of parent (original atom ex. Uranium) D = amount of daughter product (new atom ex: Lead) For a particular radioactive element in a rock, determine the present ratio = D/P. D P

Half Life = Number of years for 1/2 of the original number of atoms to decay

The Principle of Uniformitarianism Radiometric Dating Assume: Rate of decay (half life) of long-lived elements has not varied since the Earth was formed. This is an example of uniformitarianism. The Principle of Uniformitarianism The physical, chemical and biological laws that operate today have also operated in the geologic past.