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Identify Index Fossils
Transcript of Identify Index Fossils
On your 4.5 meter geological timeline, about where would trilobites first appear? (You may need your notes.)
Trilobites appeared toward the beginning of the Cambrian period, which was at the start of the Paleozoic era. They would be near the heavy line between the Paleozoic era and Precambrian time, on the today side of the line.
Relative Scale and Magnification
Which one of these fossils is wider at its widest point? Composita trilobata or Ovatia. (Use the scales)
Composita trilobata is larger. Even though Ovatia is drawn larger, it is at a higher level of magnification.
* Some fossils also provide evidence for the age of rock layers.
Fossils provide geologists with important evidence about prehistoric environments.
* These fossils are called
Not all fossils are index fossils.
must have lived for a relatively short period of time an in many place
They know it is about the same age as any other rock layers that contain the same index fossil.
If geologists identify an index fossil in a rock layer, they can be pretty sure of the age of the rock layer in which it was found.
A fossil that lived for only a million years or so would be a good index fossil.
You would know that any rocks containing that fossil are no more than a million years different in age.
For example, some of the same index fossils are found in rocks of Devonian age in both the Grand Canyon and in the Midwest.
An index fossil should be distributed over a wide geographical area to be useful.
Which would make a better index fossil, a fern that has lived on Earth since the Pennsylvanian period, 300 mya, or a trilobite that lived for only a few million years during the Cambrian period?
The trilobite would make a better index fossil because it lived for a relatively short time over much of Earth.
The rock layers at the Grand Canyon and a sample of the fossils that have been found in each layer.