Some organisms have structures that record their ages.

For example, annual wood rings are formed as a tree trunk grows.

The growth rings tell us how long an individual has lived.

This is a cross section of a fossil tree trunk.

Notice each of the annual growth rings.

By counting the number of rings (one per year), we can determine how many years the tree lived before it died.

Count the number of growth rings. How long do you think this tree lived?

a) Fewer than 6 years
b) 6 to 10 years
c) More than 10 years

This tree seems to have been about 14 years old when it died.

Try looking at this picture again. Notice how wide each of the growth rings is.