Scientific methods of dating the earth
Before the advent of absolute dating methods in the twentieth century, nearly all dating was relative.
The main relative dating method is stratigraphy (pronounced stra-TI-gra-fee), which is the study of layers of rocks or the objects embedded within those layers.
When carbon-14 falls to Earth, it is absorbed by plants.
Absolute dating methods are carried out in a laboratory.
Narrow rings grow in cold or dry years, and wide rings grow in warm or wet years.
The rings form a distinctive pattern, which is the same for all members in a given species and geographical area.
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.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.
When the organism dies, the supply stops, and the carbon-14 contained in the organism begins to spontaneously decay into nitrogen-14.