A fossil is the preserved remains of a dead organism from millions of years ago. Fossils are found in rocks and can be formed from:
Fossil remains have been found in rocks of all ages. Fossils of the simplest organisms are found in the oldest rocks, and fossils of more complex organisms in the newest rocks. This supports Darwin's theory of evolution, which states that simple life forms gradually evolved into more complex ones.
Evidence for early forms of life comes from fossils. By studying fossils, scientists can learn how much (or how little) organisms have changed as life developed on Earth.
There are gaps in the fossil record because many early forms of life were soft-bodied, which means that they have left few traces behind. What traces there were may have been destroyed by geological activity. This is why scientists cannot be certain about how life began.
Fossils provide a snap shot of the past and allow us to study how much or how little organisms have changed as life developed on Earth.
Evolutionary trees are used to represent the relationships between organisms. Branches show places where speciation has occurred, and a new species has evolved.
In this evolutionary tree, species A and B share a recent common ancestor. Species A is therefore most similar to species B.
Species F and G also share a recent, yet different, common ancestor, which itself shared a common ancestor with species E. All seven species share a common ancestor, probably from the distant past. The information is collected from a variety of sources such as fossil records to DNA sequences.