2 - nature of fossil record Flashcards
What steps are required for a useful fossil to form and be found
an organism must:
1) Die and avoid destruction by biological processes
2) be transported into an environment where it is deposited and incorporated into sediment
3) organism can then be fossilised by a number of processes (traphonomy) - as sediment piles up squeezes out liquid +gas
4) The sediment must then avoid metamorphic processes or destruction via erosion
5) Fossil must become exposed at the surface and discovered
How reliable is the fossil record
The fossil record is incomplete and biased.
why is the fossil record incomplete
1) sediment only accumulate over a very small area of the planet
2) Only a tiny fraction of organisms that ever lived will be fossilised
3) most will be destroyed
4) tiny % of formed fossils are found + studied
Why is the fossil record biased
1) certain organisms + parts are preferentially preserved. anything without an endo/exoskeleton is unlikely to be preserved
2) certain environments preferentially preserve sediment and hence fossils
3) Older rocks are more likely to be destroyed
4) collector bias
What types of organisms leave a fossil record and which parts
1) Bacteria - certain bacterial sheathes and structures left by bacteria
2) Protists - those that form exo/endoskeletons
3) Plants - Woody tissues (lignin) , cuticle (cutan), spores
4) Funghi - chitonous spores and hyphae
5) Animals - those with recalcitrant exo and endoskeletons
Where does sediment accumulate
- Inland basins (not extremely common)
- Flood plain ( trapped en route from mountains to sea)
- sea shelf (all sediment from land piles out onto shelf)
How does fossil preservation on mountains work
No preserves on mountains - for mountain organism to be preserved it needs to fall/be eroded into flood plain or basin.
What can happen when sediment builds up on the continental shelf
- Sediment piles up on shelf and causes an avalanche into the deep ocean causing a turbidity current
How is sediment preserved in the deep ocean
- most sediment in deep sea is destroyed by plate tectonics
- Very poor fossil record of the deep ocean
- In middle of ocean you find red clay as there is no sediment present (i.e. no fossils)
what areas have a huge bias of fossil formation
1) inland basin
2) flood plain
3) continental shelf .
what is sediment
Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid.
Example of a long term environmental change that affects the fossil record
Sea level change
- the higher the sea level the larger the continental shelf is
- currently we have a small amount of shelf
What effect does continental configuration have
Affects:
1) area of shelf
2) tectonic activity
3) sediment production
i.e. when earth was Pangea it had a dramatically reduced amount of continental shelf
reduced shelf = reduced biodiversity and reduced sediment build up
How does atmospheric condition affect sediment
effects weathering rate and sediment production/ survival of fossils
what is the fossil record and how is it interpreted
- simply put , it is the spatial ( palaeogeographical) and temporal distribution of fossils
- to interpret the fossil we must understand the nature its incompleteness and bias
