How to Tell a Fossils Age

If fossils could talk, they could tell us exactly where they came from and how and when they ended up becoming fossilized. Unfortunately, this isn't the case. However, fossils do leave certain clues in the environment that can help determine their age. In fact, the age of the very ground or rock it was unearthed from may indicate how long a fossil was laid to rest before taking up residence in a museum. Still, dating the specific age of fossils can be a tricky business. That's why paleontologists use a variety of other methods to tell a fossil's age.

Instructions

Difficulty: Moderately Challenging

Learn How Scientists Can Tell a Fossil's Age

1. Understand that you can't tell the age of a fossil by simply looking at it, especially with an untrained eye. A bone fragment found in a farmer's field, for instance, could have been left behind by a dinosaur, or it could be a chicken bone tossed aside at last summer's family picnic.
2. Know that there are two methods of dating fossils employed by the scientific community: absolute and relative.
3. Follow the relative method, a dating technique that's been in use for about 200 years, to tell a fossil's age. By this method, the age of the sedimentary rock surrounding the fossil is estimated based on its correlation to the geologic column. This simply means that if a layer of rock that housed the fossil is known to belong to the Cambrian Period, then the fossil likely deposited around that time.
4. Be aware that not all fossils can be dated using the relative method, nor is the method itself without flaw. For instance, environmental disturbances may not allow for the exact placement of certain regions in the geologic column.
5. Learn that absolute dating, also known as carbon-14 dating, relies upon the availability of enough organic material being present in the fossil to measure a radioactive isotope and its by-product, carbon-14. Since the rate of expiration of the isotope is known to be constant, the scientist can tell a fossil's age by comparing the amount of isotope present to the amount of the by-product. This method can be used to date fossils up to 40,000 years old. Older specimens are dated by measuring other by-products, such as uranium-235.
6. Learn more about how the age of fossils is determined and view sample specimens from the American Museum of Natural History (see Resources below).

Tips & Warnings

• If you think you may have a rare fossil in your possession, contact the science department head of a reputable university or natural history museum.