Absolute dating methods are used to determine an actual date in years for the age of an object.
Before the advent of absolute dating methods in the twentieth century, nearly all dating was relative.
Stratigraphy: Study of layers of rocks or the objects embedded within those layers.
The age of the remains of plants, animals, and other organic material can be determined by measuring the amount of carbon-14 contained in that material.
The successive layers of rock represent successive intervals of time.
Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Correlation with them has helped geologists date many New Zealand rocks, including those containing dinosaurs.
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.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.
If a certain kind of pollen is found in an archaeological site, scientists can check when the plant that produced that pollen lived to determine the relative age of the site.