| 7. Evidence of the events in Earth's history is found within the rocks. |
Fossils buried within the rock layers are evidence for the events in Earth’s history.
Click on each of the fossils shown to find out what they are.
We can apply the Law of Superposition to the fossils as well as to the
rocks. Which of the fossils is the earliest (oldest)?
| a.) Brachiopod |  |
| b.) Eurypterid |  |
| c.) Trilobite |  |
| d.) Ammonite |  |
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Trilobites ("three lobes") are so called because their bodies are
divided into three lobes: a middle lobe and one on either side. They first
appeared about 540 million years ago. |
Ooops! Remember that the Law of Superposition means that the oldest rocks and fossils will be at the bottom! Try again.
Great! You remembered that the Law of Superposition means that whatever fossil is at the bottom of the sequence of rocks is the earliest or oldest. That’s the trilobite!
These
are ammonites, a chambered mollusc not unlike the living Nautilus.
Ammonites went extinct at the same time as the dinosaurs, about sixty-five
million years ago.
The eurypterids
were one of the fiercest predators in ancient seas. Some reached more than
two meters (six feet) in length, making them the largest arthropods that ever
lived. The last ones went extinct about 245 million years ago.
Brachiopods
are marine animals that look a bit like clams. They are still common in cold
waters today, but the height of their diversity occurred about 400 million
years ago.