AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Fossils: Fossils may be formed:
This statement introduces the different ways fossils can form.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 2 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This statement introduces the different ways fossils can form. Fossils form when an organism or its traces are preserved before they decay completely. Common routes include: rapid burial in sediment, so decay is limited and hard parts remain; preservation of an impression or mould when an organism dissolves and leaves a cavity that may later fill with minerals to make a cast; replacement of hard parts by minerals, turning bone or shell into rock-like material; and preservation in amber, tar or ice, where decay is prevented. Fossils can also be traces such as footprints, burrows or droppings. The method depends on conditions: hard parts, quick burial, low oxygen and stable temperatures all help.
For example: A shell buried in mud may dissolve and leave a mould, while an insect trapped in amber may survive almost unchanged.
What earns the marks
- Identifies rapid burial in sediment as a route to fossil formation, limiting decay and scavenging.
- Describes preservation of hard parts such as bones, shells, teeth or wood, which resist decay better than soft tissue.
- Explains moulds, casts or impressions, where an organism leaves a cavity or shape that may later be filled by minerals.
- Recognises preservation in amber, tar or ice, where decay is prevented and even soft parts may survive.
- Includes trace fossils such as footprints, burrows or droppings as evidence of organism activity.
Common mistakes and how to put them right
Listing only one method when the question asks how fossils may be formed.
Put it right by giving at least two distinct routes, such as rapid burial and preservation in amber.
Confusing a mould with a cast.
Put it right by stating that a mould is a cavity left by a dissolved organism, while a cast forms when that cavity fills with minerals.
Claiming soft parts always decay before fossilisation.
Put it right by noting that amber, tar and ice can preserve soft parts because decay is prevented.
Exam tips
- Use the command word ‘may be formed’ to justify giving more than one method, each with a brief explanation.
- Name the material or condition involved, such as sediment, minerals, amber, tar or ice, to show precise knowledge.
- Link each method to why decay is prevented or limited, for example rapid burial, low oxygen or low temperature.
Try the lesson
The start of the Fossils: Fossils may be formed: lesson, made from checked teaching notes for this specification point.
Have a go first
Which process can form a fossil?
Listen
This statement introduces the different ways fossils can form. Fossils form when an organism or its traces are preserved before they decay completely. Common routes include: rapid burial in sediment, so decay is limited and hard parts remain; preservation of an impression or mould when an organism dissolves and leaves a cavity that may later fill with minerals to make a cast; replacement of hard parts by minerals, turning bone or shell into rock-like material; and preservation in amber, tar or ice, where decay is prevented. Fossils can also be traces such as footprints, burrows or droppings. The method depends on conditions: hard parts, quick burial, low oxygen and stable temperatures all help. For example, a shell buried in mud may dissolve and leave a mould, while an insect trapped in amber may survive almost unchanged. A strong answer earns marks for these points. Identifies rapid burial in sediment as a route to fossil formation, limiting decay and scavenging. Describes preservation of hard parts such as bones, shells, teeth or wood, which resist decay better than soft tissue. Explains moulds, casts or impressions, where an organism leaves a cavity or shape that may later be filled by minerals. Recognises preservation in amber, tar or ice, where decay is prevented and even soft parts may survive. A common slip: Listing only one method when the question asks how fossils may be formed. Instead, giving at least two distinct routes, such as rapid burial and preservation in amber. Exam tip: Use the command word ‘may be formed’ to justify giving more than one method, each with a brief explanation.
See it
Key words
Say what each word means before you turn the card.
Rapid burial and decay prevention
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Hard part preservation
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Moulds, casts and impressions
Try answering aloud or in your head before turning the card.
Preservation in amber, tar and ice
Try answering aloud or in your head before turning the card.
See every definition
- Rapid burial and decay prevention
- Quick burial in sediment limits decay and scavenging, so hard parts remain.
- Hard part preservation
- Bones, shells, teeth or wood resist decay better than soft tissue and may be preserved.
- Moulds, casts and impressions
- A dissolved organism leaves a cavity or shape that may later be filled by minerals.
- Preservation in amber, tar and ice
- Decay is prevented, so even soft parts may survive almost unchanged.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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