Q:

Why are index fossils useful to geologists?

A:

Quick Answer

More than any other type of fossil, index fossils define geological time periods for geologists by providing the most useful information about the age of the rock they are found in. Index fossils are also called key fossils or type fossils.

  Know More

Full Answer

The best index fossils have four characteristics: They are unique, prevalent, plentiful and restricted in geologic time. Most fossils are from ocean rocks, so most major index fossils are from marine organisms. However, young rocks found in certain regions are useful for revealing the fossils of land organisms.

Many kinds of organisms are unique but few are widespread. Index fossils that began life as floating eggs and in infant stages are important because ocean currents helped them populate the world. The most successful ones became abundant, but this also exposed them to environmental change and extinction. This thrive-or-die characteristic makes the best index fossils.

Trilobites are excellent index fossils for Paleozoic rocks. These mobile animals lived across oceans and constantly evolved into new species from the Middle Cambrian time to the end of the Permian Period, which is almost the entire Paleozoic period. These organisms inhabited large, even global areas, and their large fossils can be studied without a microscope. Similar index fossils include rugose corals, crinoids, mollusks, ammonites, bryozoans and brachiopods.

Other index fossils such as floating plankton are very useful because of their small to microscopic size. Their tiny bodies rained down all over the ocean and are found in many kinds of rocks, even wellbore cuttings. Index microfossils are a great asset to the petroleum industry, and have enabled geologists to break down geologic time into fine detail.

Index fossils of terrestrial rocks formed on land reveal clues about quickly-evolving small rodents as well as larger animals that ranged over wide geographic ranges.

Index fossils define the ages, epochs, periods and eras in the formal architecture of geologic time. Related fossil types are the characteristic fossil, which belongs to a time period without defining it, and guide fossils, which narrow down but don’t specify a time period.

Learn more about Geology

Related Questions

  • Q:

    Why are rocks important?

    A:

    Rocks are important because geologists use evidence from them to learn about what the Earth was like in the past. They allow scientists to build a historical record of the planet to learn what events occurred before people lived.

    Full Answer >
    Filed Under:
  • Q:

    What are some examples of a stratigraphic column?

    A:

    Stratigraphic columns are illustrations made by geologists to represent the relative composition, thickness and scope of layers of rock, such as in a canyon, a volcano or a cliff. Some drawings are black and white with labeled layers, while others have colors that more closely resemble layers of rock described in the column. Each layer is distinct, and geologists label the general composition of each portion.

    Full Answer >
    Filed Under:
  • Q:

    How are fossils formed?

    A:

    Live Science explains that fossilization can occur in a number of ways, the most common of which is called petrification. Once the soft organic tissues such as skin and muscle decay, the bones and other hard parts remain intact. As water covers the remains, minerals dissolved in the water seep into the bones, causing crystallization and preservation.

    Full Answer >
    Filed Under:
  • Q:

    What are the five types of fossils?

    A:

    Five of the most common types of fossils include mold and cast, trace, body, compression and petrifaction. Each type of fossil forms differently and is preserved by more than one method.

    Full Answer >
    Filed Under:

Explore