fossils and time Flashcards
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What is a fossil?
Traces or remains of past life, including body fossils (hard parts like shells, skeletons) and trace fossils (footprints, burrows)
What is taphonomy?
The study of fossilisation processes
What’s the difference between a mould and a cast?
- Mould: A void left after dissolution of a shell/body
- Cast: In-filling of a mould by another mineral
Name five factors that affect fossilisation
- Original Composition
- Energy Levels
- Transport Distance
- Size of Sediment
- Diagenesis
What are the main types of fossil preservation?
- Replacement
- Silicification
- Carbonisation
- Pyritisation
- Mould and Cast Formation
What is carbonisation?
The process where organic matter decomposes under heat and pressure, leaving a carbon film. Common in plants and soft organisms.
What is pyritisation?
Replacement of fossil material by iron pyrites in anaerobic environments with high sulfur content
What’s the difference between aragonite and calcite?
Both are CaCO₃ polymorphs but:
* Aragonite: Unstable, alters to calcite over time
* Calcite: More stable, often translucent
What are benthonic organisms?
They live on the sea floor or sediment.
What’s the difference between planktonic and nektonic organisms?
Planktonic float with currents, while nektonic swim actively.
What is a life assemblage?
Fossils preserved in life positions (e.g., burrowers in burrows).
What is a death assemblage?
Fossils transported away from their life positions.
What do robust fossils indicate?
High-energy environments.
What do thin-shelled fossils suggest?
Low-energy environments.
Where are trace fossils most commonly found?
In low-energy, fine-grained sediments.
