This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks.Geologists have established a set of principles that can be applied to sedimentary and volcanic rocks that are exposed at the Earth's surface to determine the relative ages of geological events preserved in the rock record.
Relative dating methods do not tell archaeologists exactly how old things are, but only how old things are relative to each other.
Archaeologists work on the principle that objects at the bottom of an undisturbed were put there before objects that are above them, so objects found in the lower levels of a site are usually older than objects found in higher levels.
This method is useful for archaeologists working in areas where volcanic eruptions have left layers of ash above and below an archaeological deposit.
The volcanic layers can be dated, and the archaeological material will date to the period between those two volcanic eruptions.
As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.