How to Date Fossil Remains

Fossils are some of the most useful things in the geologic record for telling the ages of rocks. However, the rocks can also help to tell the ages of the fossils. But, to tell how these relate to one another is a challenging exercise. Fossils are dated "absolutely" through chemistry of the fossils and the rocks they are found in and "relatively" using the fossils themselves. Use these steps to date fossil remains.

Instructions

Difficulty: Challenging

Things You’ll Need:

• Guidebook of fossil identification
• Hand lens

Relative Dating

1. Identify the fossils from a deposit that you are interested in. It is typically easier to determine the age of a group of fossils found together than one isolated fossil. Use a guidebook to help you do so. A good example of a guidebook that can help you identify most fossils is the "National Audubon Society Field Guide to North American Fossils," published by Alfred A. Knopf. Other, more specialized guidebooks can help you in identification, as well.
2. Take note of the age ranges of the fossils that you have identified. Your guidebook will give you the age ranges of the fossils. Once you have identified the fossils from your guidebook, the age ranges during which these fossils lived can help you figure out during which time period your fossils were buried. An example of an age range of a fossil might be Middle Devonian to Late Devonian.
3. Make a chart of the age ranges of all of the fossils that you have identified in steps 1 and 2 above. Put a standard geologic time scale along the top of your chart. Below this, put a row showing the age range of each fossil.
4. Determine the age of the group of fossils by locating the overlap in age ranges. The precision of the age of the fossil group may vary depending on the fossils involved.

Absolute Dating

5. Determine which dating technique is best for the fossils that you want to date. Different dating techniques require different methods for data collection and sampling. Consult a book on the absolute dating of fossils, such as Historical Geology: Evolution of Earth and Life Through Time, published by Brooks Cole. Examples of dating include radiometric dating, paleomagnetic dating and the dating of biological markers such as amino acids.
6. Collect samples that are appropriate for the dating technique selected for your fossil. Take careful note of how your rock samples relate to your fossils of interest.
7. Talk to technicians at the laboratory where you'll have your fossils dated. Often, local colleges and universities will have labs that will date fossils for you. Make sure you talk about where your samples came from and what you are trying to date and accomplish.
8. Send your samples to the laboratory you have chosen as per their instructions.
9. Assess the findings. If possible, compare your absolute dating to the relative dating.

Tips & Warnings

• If you find that your fossils have age ranges that do not overlap, you may have misidentified one or more of your fossils. Try consulting a different fossil identification guidebook.
• When dating a fossil, you are in actuality dating the layer of rock in which it was found.