GEOLOGY

Detailed explanation-1: -The oldest fossils are between 3 billion and 3.5 billion years old. These are fossil bacteria, and for most of Earth history, life was simple. More complex animals appeared in the oceans about 565 million years ago, and became much more common about 542 million years ago.

Detailed explanation-2: -RELATIVE AGE OF ROCKS Index fossils are commonly used to match rock layers in different places. You can see how this works in Figure. If two rock layers have the same index fossils, then they’re probably about the same age.

Detailed explanation-3: -Using the principle of faunal succession, if an unidentified fossil is found in the same rock layer as an index fossil, the two species must have existed during the same period of time (Figure 4). If the same index fossil is found in different areas, the strata in each area were likely deposited at the same time.

Detailed explanation-4: -If the same index fossil is found in different strata far apart, the layers likely formed around the same time. By studying strata, geologists have determined the relative order of major events in Earth’s history. The timeline of these events is called the geologic time scale.