Various methods exist differing in accuracy, cost and applicable time scale.All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances.It is our principal source of information about the age of the Earth and a significant source of information about rates of evolutionary change.This is shown below: The Angular Unconformity The strata A to E was deposited first, tilted, subjected to erosion (peneplained) and submerged.Strata X to Z were laid down horizontally on top of the older beds.After one half-life has elapsed, one half of the atoms of the substance in question will have decayed.
In each period of earth's history different fauna and flora evolved with similar faunas being characteristic of similar beds.
The diagram right shows two distinct faunal assemblages.
What can be deduced from our two distinct faunas in terms of their usefulness in the relative dating of rocks?
The laws of physics and chemistry that governed geologic processes in the past are the same as those that govern processes now and in the future.
The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.