AQA GCSE Combined Science: Biology

Revision Notes

6.3.5 Fossils

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

How fossils are formed table, downloadable IGCSE & GCSE Biology revision notes

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)

Evolutionary tree primates, downloadable IGCSE & GCSE Biology revision notes

An evolutionary tree for five species of primate

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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