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Geology Facts

What is an ammonoid?

Ammonoids are frequently found as fossils in marine rock from the Devonian to the Cretaceous periods. Ammonoids date from 408 to 66.4 million years ago. Relatives to the modern-day pearly nautilus, ammonoids are extinct cephalopods. Ammonoid shells are either straight or coiled and serve as protective and supportive structures and also enabling the animal to compensate for varying water depths. Ammonoids are great index fossils due to their wide geographic distribution in shallow marine waters, their rapid evolution and their easily recognizable features.

Click here to view a picture of an ammonoid.

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What is a geologic time scale?

A geologic time scale represents the “calendar of events” in Earth’s history. The fossil forms that occur in rock strata provide the chief means of establishing a geologic time scale. Particular types of organisms are characteristic of particular parts of the geologic record. The geologic time units in descending order of duration are: Eons, Eras, Periods and Epochs.

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What is geologic time?

Geologic time is the segment of Earth history that is represented and recorded in rock strata.

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What is the Grenville Orogeny?

The Grenville Orogeny is a mountain-building episode that took place ~ 1 billion years ago.

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