fossils Flashcards
fossils
are the preserved remains or traces of once living organisms
mould
a hollow area of a rock that is in the shape of an organism or part of an organism
Cast
a solid copy in the rock of the shape of an organism
body fossils
show us what an organism looked like. they are the fossilised remains of an organism, eg bones, leaves, shells
trace fossils
provides evidence of the activities of once living organisms eg footprints, coprolites, burrows, teeth marks
fossil formation stages
- organism dies and is covered by sediment
- soft parts decay leaving just the hard parts. pressure turns sediment into hard rock
- hard parts dissolve, leaving a mould in the shape of the organism
- mineral rich water fills the hollow part. cast is formed when minerals crystallise
conditions required for fossilisation
- quick burial as it means that the organism or the parts of it are less likely to be scattered or eaten
- suitable body parts - hard body parts are easier to fossilise than soft parts
- little geological disturbance - rock cycle is destructive, and when sedimentary rock is altered or destroyed, the fossils are likely to be too
what can fossils tell us?
fossils form in sedimentary rock, which forms in layers underwater. thus, by the law of superpostion, whereby the oldest rock layer is at the bottom and the youngest at the top, we can determine the relative age of fossils.
principal of uniformitarianism
the assumption that the processes that operate in our present scientific observations also operated in the past in the universe, and also apply everywhere in the universe.
relative dating
used for determining whether an object or event is older or younger than other objects/events
law of superpostion
in an undisturbed stack of sediment layers, the oldest layer is at the bottom and the youngest at the top
original horizontality
when it is first deposited, sediment is always laid down in horizontal layers, however these can be tilted or bent into folds by subsequent geological activities
law of cross cutting relationships
any continuous geological structure that cuts across another is the younger structure eg igneous dykes
law of inclusions
a large piece of material included within a rock layer is older than that layer
unconformity
a missing layer of rock that forms a gap in the geological record. is formed when rock layers are eroded or when sediment is not deposited for a long time
