Fossils (AQA GCSE Biology)

How are Fossils Formed?

• Fossils are the ‘remains’ of organisms from millions of years ago, which are found in rocks

• Fossils may be formed in several ways:

How fossils are formed table

Gaps in the Fossil Record

• Many early forms of life were soft-bodied, which means that they have left few traces behind – soft tissues often decay fully, leaving no trace in the fossil record

• What traces there were have been mainly destroyed by geological activity (eg. tectonic plate movements may have crushed fossils that had already formed)

• This is why scientists cannot be certain about how life began on Earth

Changing Planet

• Evidence for early life forms on Earth can be found in the fossil record

• We can learn from fossils how much or how little different organisms have changed as life developed on Earth

Evolutionary trees

• Evolutionary trees are diagrams that show the relationship between species over evolutionary time

• A new branch in the tree shows where speciation has occurred (when a new species has evolved)

• In the evolutionary tree below, for example:

  • Chimpanzees and bonobos share a recent common ancestor. Chimpanzees are therefore most similar to bonobos (more similar than they are to any other primate species)

  • Humans share a more recent common ancestor with gorillas than they do with orangutans – this means we are more closely related to gorillas than we are to orangutans

  • All five primate species shown here share a common ancestor (from the distant past)

An evolutionary tree for five species of primate