Relative and Absolute AgeLaw of Superposition

Relative and Absolute Dating

There are two major ways to date geologic events:

Relative dating-how old a rock is compared to surrounding rocks

Absolute dating-actual number of years since the rock was formed

Relative Dating

The various relative dating methods tell you whether a specific rock or layer of rocks is younger or older as compared to surrounding rocks

This type of dating does not give an exact age for the rock

• The Law of Superposition states that in an undisturbed sequence of sedimentary rock:Each layer is older than the one aboveEach layer is younger than the one below

Law of Superposition

• a vertical set of strata (layers) is a chronological record of the geologic history of that strata

• Youngest layers are on top and oldest on bottom

Law of Superposition

• Absolute Dating

– Absolute dating can give you the exact age of a rock

– This is accomplished using radioactive dating, which is also referred to as radiometric dating

– Based on the regular radioactive decay of certain elements