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.
What is a trace fossil?
A record of activity (e.g., tracks, burrows), not the organism itself.
What can dinosaur footprints reveal?
Size, behavior, and speed.
What do U-shaped burrows indicate?
Feeding or dwelling behavior.
What is catastrophism?
The theory that Earth’s features formed through short-lived, violent events like volcanic eruptions and earthquakes.
Who used fossil evidence to establish extinction as a fact?
Georges Cuvier (1769–1832).
How old did Archbishop Ussher calculate Earth to be, based on the bible
6,000 years old, based on the Bible.
What does gradualism propose?
Changes occur slowly over long periods, contrasting catastrophism.
Who is the “Father of Geology”?
James Hutton (1726–1797).
What concept did James Hutton develop?
The “great geological cycle.”
What is uniformitarianism?
The idea that “the present is the key to the past.”
What does uniformitarianism claim?
Geological processes observable today occurred at similar rates in the past.
What is the sedimentation rate for calcareous ooze?
0.01–0.1 mm/year.
What is the sedimentation rate for sandstones?
10–1,000 mm/year.
Which sediment type has the highest deposition rate?
Conglomerates: 50–50,000 mm/year.
Who created the first geological map of England and Wales?
william Smith (1769–1839).
What did William Smith recognize about rock layers?
They contained distinct fossils.
What is William Smith known as?
The “Father of English Geology.”
What are unconformities?
Gaps in the geological record where deposition stopped and erosion removed layers.
What is the rock cycle?
Interaction of processes like erosion, sedimentation, magma formation, and crystallization.
