Fossils Flashcards
what are fossils
remains or traces of organisms from a past geological age embedded in rocks or other substances by natural processes
what is fossilisation
when an organism or its traces are buried quickly so that weathering and total decomposition does not occur
what is a transitional fossil
a fossil or organism that shows the intermediate state between an ancestral form and that of its descendants, also known as a ‘missing link’
how are fossils dated simply
sedimentary rock forms layers of silt or mud on top of each other the deeper the layer, the older the rock
what is absolute dating
a method that uses the amount of radioactivity remaining in the rock surrounding the fossil to determine its age
what is a living fossil
existing species of ancient lineages that have not changed form for a very long time
why are there living fossils
the selection pressures for these organisms have not changed and therefore there is no pressure for the organism to change
how are fossils formed
organism dies at bottom of water, organism is covered by sediment, soft tissues decompose and hard body becomes fossilised, sedimentary layers accumulate - pressure forms sedimentary rock, earths movements raise layers of rock to the surface, rock erodes
what are the conditions for fossilisation
areas of rapid sediment accumulation, constant cool temps, low light, physical protectors from scavengers and decomposers
how do index fossils determine fossils age
If your target fossil is found in the same sedimentary layer as this index fossil, then the age of the two fossils are approximately the same.
If your fossil is found in a higher or lower sedimentary layer it will be younger or older respectively
what is carbon dating
a type of radiometric dating the uses The ratio between carbon-12 and carbon-14 can be used to determine the absolute age
how does carbon dating work
Most of the carbon contained in living things is carbon-12, but there is also a small amount of the radioactive isotope carbon-14. When an organism dies, the unstable carbon-14 decays, but the carbon-12 does not.
