Identify and describe What Are Fossils?, Conditions Required for Decay and What Fossils Tell Us About Evolution in the context of fossils.
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GCSE Biology Revision
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GCSE Biology revision
Fossils
The development of understanding of genetics and evolution
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AQA student objectives
Learning pathway
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Explain the relationships between What Are Fossils?, Conditions Required for Decay and What Fossils Tell Us About Evolution and how they contribute to fossils.
Apply and analyse knowledge of What Are Fossils?, Conditions Required for Decay and What Fossils Tell Us About Evolution to interpret unfamiliar information about fossils.
Revision summary
Key knowledge
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What Are Fossils?
- Fossils are the preserved remains of dead organisms, formed over millions of years when certain body parts do not decay and eventually turn to rock through weathering.
- Hard structures such as shells and bones are most commonly preserved, along with traces like footprints, rootlets, and burrows.
Conditions Required for Decay
- For decay to occur, three key conditions are needed: suitable temperature, oxygen, and water.
- When these conditions are absent — for example in peat, ice, tar, or amber — organisms can be preserved rather than decayed.
What Fossils Tell Us About Evolution
- Fossils of simpler organisms tend to be found in older rocks, whilst fossils of more complex organisms are found in newer rocks, reflecting Darwin's theory that life developed from simple to complex forms.
- Some of the oldest life forms had soft bodies, meaning very little physical material was left behind to fossilise.
- Geological activity such as tectonic plate movement and earthquakes has destroyed the majority of fossil evidence over time.
Limitations of the Fossil Record
- The fossil record is incomplete, making it difficult to build a full and accurate picture of how life has developed over time.
- Despite their limitations, fossils remain a valuable tool for tracking the broad development of life on Earth.
What Are Evolutionary Trees?
- Evolutionary trees (also called phylogenetic trees) are diagrams used to map the evolutionary relationships between different organisms.
- All organisms on an evolutionary tree share a common ancestor, shown by the single branch from which all others stem.
- Each branching point on the tree represents a speciation event, where two groups of the same species become so different they can no longer interbreed to produce fertile offspring.
Interpreting Evolutionary Trees
- Organisms that branch apart from each other more recently on the tree are more closely related and therefore more similar to one another.
- Organisms that branch apart from each other further back in the tree are more distantly related and therefore more different from one another, even though they share a common ancestor.
- The position of the branch points, not the position of the labels, is what determines how closely related two organisms are.