Fossils Flashcards
what is the fossil record
changes in organism over time can be observed in fossils
What is the main issue with the fossil record
not all animals create fossils
ie. soft-bodied organisms do not create fossils
What is the Law of Superposition?
depending on their position in the rock layer, you can determine the age of the fossil (similar aged fossils are near each other)
define stratigraphy
analysing rock sequences in strata (rock layer)
define fossil
any evidence of a once-living organism from the distant past
what are the types of fossils
4 types
- original fossils (eg. preserved remains)
- indirect fossils (eg. traces and imprints)
- replacement fossils (eg. petrified ‘replica’ of bone or shell - minerals have slowly replaced the original material during decay)
- carbon film fossil (just the carbon part of the fossil)
how do fossils form?
form when an organism died
1. it is quickly covered in sediment so that…
2. no other creature can eat it and…
3. no oxygen or micro-organisms get in to cause decay
where can fossils form?
- river bed, sea bed, lake bed
- swamps
- some extreme environments (hot dry deserts, frozen environments)
what type of rock do fossils form in?
sedimentary rock
igneous and metamorphic are subject to heat, which destroy fossils
how are fossils discovered?
old sedimentary rock is pushed up from underground through faults or folds
* weathering and eroison expose the fossil
what is relative dating?
comparing the age of fossils to determine which is older
does not determine the actual age of the fossil
for what 2 places is relative dating used?
- rock layers
- index fossils
how is relative dating used in rock layers?
the deeper the strata in sedimentary rock, the older it is (Law of Superposition)
fossils in the same layer are the same age
how is relative dating used in rock layers?
the deeper the strata in sedimentary rock, the older it is (Law of Superposition)
fossils in the same layer are the same age
how is relative dating used in index fossils?
index fossils are fossils that are used to compare the age of rock layers at different locations