3 laws of relative dating
(relative geologic timescale) (b) Absolute Dating Following the discovery of radioactivity in 1895, radiometric dating techniques were developed to determine the absolute ages, i.e. In the succession of strata, each layer represents the geographical conditions that occurred over that area at the time the layer was deposited.
In each period of earth's history different fauna and flora evolved with similar faunas being characteristic of similar beds.
Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.
This matching process is called correlation, which has been an important process in constructing geological timescales.
The table below summarises key features: Gastrioceras listeri is a particularly good example of a ZONE fossil.
As it is free swimming it could have travelled a considerable distance.
Relative dating is used to arrange geological events, and the rocks they leave behind, in a sequence.
The method of reading the order is called stratigraphy (layers of rock are called strata).
Strata X to Z were laid down horizontally on top of the older beds.
Throughout the history of life, different organisms have appeared, flourished and become extinct.
Many of these organisms have left their remains as fossils in sedimentary rocks.
Some of the most useful fossils for dating purposes are very small ones.
For example, microscopic dinoflagellates have been studied and dated in great detail around the world.