Great Index Fossils Tell a Tale

Index Fossils tell TaleWhat is an index fossil and why should we care about them? Well, index fossils are very important to geologists because they help to tell the tale of our Earth’s history. Geologists use these specific fossils to determine the relative age of rock layers and to correlate those rock layers worldwide. Sound far-fetched? It isn’t really. Some fossils have such unique characteristics that if you find them, you know exactly where you are in the age of Earth. Good index fossils lived for only a short period of time but lived all over the world.

Easy to Identify
One key of a good index fossil is that it is easy to recognize in the field without the use of specialized equipment. Field geologists like to identify a specimen quickly and move on the next sampling area with confidence. A great example of a unique-looking fossil is the trilobite, pictured above. These marine arthropods were characterized by rounded heads and segmented bodies. There were many varieties of trilobites; however, their appearance was similar, thus making them easy to identify in the field.

There Were Lots and Lots of Them
Good index fossils were very abundant while they lived. It is easy for a field geologist to correlate a rock layer if the fossils are easy to spot in the rock. Animals and plants that were not abundant have a small chance of actually becoming a fossil. For example, trilobites were a prevailing marine animal during their lifetime. The odds that they would become a fossil were more likely than less dominant animals. Of all living plants and animals only small percentage become fossils, which makes it more likely to find the most abundant organisms of their time.

Homes Throughout the World During a Specific Time Period
In order for geologists to correlate a rock between continents; the animal or plant must have lived all over the world during a short time period. Our friends the trilobites lived all over the world during a specific time period, the Cambrian and Ordovician periods of the early Paleozoic Era, which was 443 to 543 million years ago. Therefore, if you find trilobites on different continents, you can be sure that the rocks formed during this time frame. The USGS has a list of index fossils for different time periods.

Mini Me Geology has a great selection of fossils that are sure to add some fun to your collection. Visit our fossil section today to choose your favorite!




One Response to “Great Index Fossils Tell a Tale”

  1. Thanks for posting some clear and concise information about index fossils. Most other sites are either too technical, or just not very well written. But this article perfectly delivers the information in a way that isn’t boring.

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