Radiometric dating is used to tell the age of rocks
Droughts and other variations in the climate make the tree grow slower or faster than normal, which shows up in the widths of the tree rings.
These tree ring variations will appear in all trees growing in a certain region, so scientists can match up the growth rings of living and dead trees.
Using logs recovered from old buildings and ancient ruins, scientists have been able to compare tree rings to create a continuous record of tree rings over the past 2,000 years.
This tree ring record has proven extremely useful in creating a record of climate change, and in finding the age of ancient structures. The thick, light-colored part of each ring represents rapid spring and summer growth.
Today scientists know his estimate was too young; we know that this occurred about 530 million years ago.These thick layers alternate with thin, clay-rich layers deposited during the winter.The resulting layers, called varves, give scientists clues about past climate conditions.In regions outside the tropics, trees grow more quickly during the warm summer months than during the cooler winter.This pattern of growth results in alternating bands of light-colored, low density "early wood" and dark, high density "late wood".