photo by Erica Marshall at flickr.com
Dating fossils can be an exciting process. The most important steps involve recording the rocks from which the fossil was harvested with as much detail and accuracy as possible. Using the information collected with existing research, it is possible to get a fairly accurate date.
Instructions
Investigation
1. In order to date a fossil, it is most essential to know where the fossil came from. When you are at the outcrop from which you plucked or chiseled out the fossil remains, record the location as precisely as is in your means. Using a GPS to mark the geographic coordinates is recommended.
2. Observe the rock from which the fossil came. First, take notes on the area in closest proximity to the found fossil. Do you see other fossils nearby? Do you see lots of shells, or does the rock feel smooth and sandy? What is the color of the rock? Record the size of grains present---do you see chunky, angular rocks cemented together or a surface so smooth you would need a microscope to investigate? Is it easy to break off rocks, or would you need a hammer? Do you see any tiny crystals poking out? Use your hand lens and rock hammer.
3. Look above and below the place where you found your fossil. Again, write down brief descriptions of your findings. Are there clear layers present, and if there are, what color are they? Do you see peachy, sandy units or thin, dark layers? Are the layers horizontal like table-tops, or do they cut each other at angles? Draw a rough sketch of what you see.
4. Give your fossil a number or code for easy identification. Once you have your fossils assigned with numbers and descriptions and have recorded the location and area from where they were found, it's time to do some research.
5. Find a field book describing the general geology of your area, and look for pictures and discussions of common fossils found. Do your fossils match? Does your description of the rocks match? Field books can be found at state geological surveys or national park bookstores. If you find your fossil and the rock descriptions match, the field book will provide the date of the rock unit and fossils within.
6. Use a fossil manual or collector handbook to search for a fossil match. Especially in this case, be sure to follow up with a geological map verification. Geological maps can be found online and at surveys, and show what rock unit is exposed at the surface. Using the geographic coordinates you recorded, find the location where the fossils were found on the map. Identify the rock formation using the map's legend. Once you have a rock formation name, you will have a range of time in which your fossil was formed. If your range is within a few thousand years, you've done well. Remember, in geology, plus or minus a millions years can be considered accurate.
7. Getting an "absolute" date, with a lower margin of error, will require more extensive dating techniques. It is not common for surveys or universities to date fossils for the public because of the great cost and time involved. Absolute dating requires detailed knowledge of the rock, expertise of which dating methodology to use, the equipment and ability to count tiny levels of radioactive isotope proportions, sophisticated mathematical modeling, and the means to repeat the process for confirmation.
However, if you'd like to know more about your fossils, take your specimens, notes, sketches and research to the local university, geological survey or park. With these materials, an expert will be delighted to confirm your findings and narrow your dating range even further.
Tags: your fossil, from which, your fossils, field book, fossil came
