Evidence for Evolution: Fossils

Fossils

Fossils are the preserved remains of organisms, often from millions of years ago, which are found in rocks. There are different ways that fossils can be formed:

1. When certain parts of the organism have not decayed. This can happen when the conditions required for decay are not present. For example, fossils can be preserved in ice, as the temperature is very low.

2. When hard body parts (e.g. bones and shells) are slowly replaced by minerals as they decay.

3. From preserved traces of organisms; for example, animals might leave behind footprints and burrows, while plants can leave spaces where their roots once were. These traces eventually become covered with layers of sediment.

The Fossil Record

Fossils of simpler organisms are found in older rocks, while those of more complex organisms are found in newer rocks. This supports the idea that simple organisms have evolved gradually over time into more complex organisms. By studying fossils, scientists can see how organisms have evolved over time.

Many early forms of life were soft-bodied organisms, which means they didn’t have a shell or a skeleton. As soft tissues often decay completely, soft-bodied organisms rarely form fossils. However, many of the fossils that did form from these soft-bodied organisms have been destroyed by geological activity, such as the movement of tectonic plates.

As there are not many fossils of the early forms of life, scientists cannot be certain about how life on Earth began.

Evolutionary Trees

Evolutionary trees are diagrams showing how different species are interconnected. The tree is organised based on information such as DNA sequences, fossil records and physical characteristics. The more similar species are, the more closely related they are.

A new branch in the tree is the point at which speciation occurred.

For example, in this evolutionary tree, species F and G share a recent common ancestor. This means that species F is more similar to species G than any other species. In contrast, species E and G are less closely related.

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