Palaeontology and Historical Geology
Palaeontology and Historical Geology tests fossilisation, index fossils, major evolutionary events and the use of fossils for correlation and dating.
Fossilisation
- Petrification (mineral replacement), moulds and casts, carbonisation, trace fossils, amber and ice preservation.
- Index fossils are short-ranging, wide-spread and abundant: trilobites (Paleozoic), ammonites (Mesozoic), nummulites (Paleogene).
Historical events
- Precambrian: stromatolites and first life.
- Cambrian explosion; vertebrates in Ordovician.
- Permian-Triassic extinction about 252 Ma, the greatest mass extinction.
- Cretaceous-Paleogene extinction about 66 Ma, ending dinosaurs.
- Gondwana flora: Glossopteris; Gondwana fauna includes Lystrosaurus.
Worked example
A limestone contains coiled, chambered shells with sutures and is asked its age. Reasoning: coiled chambered shell with complex sutures is an ammonite; ammonites are restricted to the Mesozoic. Answer: Mesozoic.
Traps
Ammonites are not nautiloids; nautiloids have simple sutures and survive today. Glossopteris indicates Gondwana (Permo-Carboniferous), not Cretaceous. A trace fossil records behaviour, not the body.