fossils Flashcards
(10 cards)
1
Q
fossils
A
the ‘remains’ of organisms from millions of years ago which are found in rocks
2
Q
gradual replacement by minerals
A
- things which don’t decay easily e.g teeth and bones are eventually replaced by minerals as they decay, forming a rock-like substance shaped like original part
- surrounding sediments turn to rock but fossil stays distinct inside the rock and eventually someone digs it up
3
Q
from casts and impressions
A
- an organism is buried in a soft material e.g clay / mud
- clay later hardens around it and organism decays, leaving a cast of itself e.g footprints, burrows, rootlet traces
4
Q
from preservation in places where no decay happens
A
- in amber and tar pits there’s no oxygen or moisture so decay microbes can’t survive
- in glaciers its too cold for decay microbes to work
- peat bogs are too acidic to work
5
Q
why can’t scientists be certain about how life began?
A
- many early forms of life were soft-bodied, which means that they have left few traces behind - traces there were have been mainly destroyed by geological activity
6
Q
what can we learn from fossils?
A
how much or how little different organisms have changed as life developed on Earth
7
Q
3 ways fossils can be formed
A
- from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
- when parts of the organism are replaced by minerals as they decay
- as preserved traces of organisms, such as footprints, burrows and rootlet traces
8
Q
how can scientists estimate when organisms were alive?
A
- compare to other fossils of known age
- by the age of the rocks where the fossil was found
9
Q
give three reasons why the fossil record is not clear for older species
A
- oldest organisms were soft-bodied so most of the tissue
decayed - more likely to be destroyed by geological activity
- fossils buried deeper so harder to find
10
Q
how do most fossilisations occur?
A
- organism dies buried in sediment
- only soft parts decayed
- mineralisation occurred
