Fossils (AQA GCSE Biology: Combined Science)

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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

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Lára

Author: Lára

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.