The association of strata and fossils arises because the rocks or sediments that make up the soil are stacked in layers that contain fossils. The oldest fossils are found in the deepest layers and the youngest or most recent ones, near the surface. It is as if the rock layers represent a vertical timeline.
In the background there are no fossils of modern animals or plants, but they are all already extinct. On the contrary, closer to the surface there are fish, amphibians and reptiles, then mammals and birds, and finally modern mammals including humans..
1- Fossils are the remains or traces of prehistoric organisms. They are more common in sedimentary rocks and in some pyroclastic materials such as ash.
They are extremely useful in determining the relative age of the strata. They also provide information on organic evolution.
2- Most of the fossils are the remains of extinct organisms, or species of which individuals are no longer alive..
3- The kinds of fossils found in rocks of different stages differ because life on earth has changed over time.
Science says that dust, mud, sand, and other sediments settle in horizontal layers. As they are stacked vertically they harden and form rocks.
If we start to examine the oldest rock layers we get to a level where there are no human fossils.
If we continue, at a certain level there are no fossils of flowering plants or birds, no mammals or vertebrates, no land plants, no oysters and no animals..
These concepts are summarized in the general principle called the law of fossil succession..
William Smith (1769-1839), an English engineer, discovered the fossil superposition principle. This principle states that the kinds of animals and plants found as fossils change over time..
When we find the same kinds of fossils in rocks from different places, we know that they are the same age..
The changes in the forms of life are recorded in the fossils of the rocks. Natural disasters or catastrophes destroy life periodically. Plant and animal species disappear and other forms of life are born.
In this way, fossils help geologists calculate the age of rocks. The groups of fossils succeed each other in a regular and determined order.
Today the marine fauna and flora is very different from the terrestrial one, and they also differ from one place to another. Similarly, fossilized animals and plants in different environments are different.
Just as animals help identify the environment, rocks help gather information about the environment in which that animal or fossil lived. Fossils in rocks follow the principle of superposition, they are consistent in different places.
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