Fossils

Question 1

what is the fossil record

Answer 1

changes in organism over time can be observed in fossils

Question 2

What is the main issue with the fossil record

Answer 2

not all animals create fossils

ie. soft-bodied organisms do not create fossils

Question 3

What is the Law of Superposition?

Answer 3

depending on their position in the rock layer, you can determine the age of the fossil (similar aged fossils are near each other)

Question 4

define stratigraphy

Answer 4

analysing rock sequences in strata (rock layer)

Question 5

define fossil

Answer 5

any evidence of a once-living organism from the distant past

Question 6

what are the types of fossils

4 types

Answer 6

1. original fossils (eg. preserved remains)
2. indirect fossils (eg. traces and imprints)
3. replacement fossils (eg. petrified ‘replica’ of bone or shell - minerals have slowly replaced the original material during decay)
4. carbon film fossil (just the carbon part of the fossil)

Question 7

how do fossils form?

Answer 7

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

Question 8

where can fossils form?

Answer 8

1. river bed, sea bed, lake bed
2. swamps
3. some extreme environments (hot dry deserts, frozen environments)

Question 9

what type of rock do fossils form in?

Answer 9

sedimentary rock

igneous and metamorphic are subject to heat, which destroy fossils

Question 10

how are fossils discovered?

Answer 10

old sedimentary rock is pushed up from underground through faults or folds
* weathering and eroison expose the fossil

Question 11

what is relative dating?

Answer 11

comparing the age of fossils to determine which is older

does not determine the actual age of the fossil

Question 12

for what 2 places is relative dating used?

Answer 12

1. rock layers
2. index fossils

Question 13

how is relative dating used in rock layers?

Answer 13

the deeper the strata in sedimentary rock, the older it is (Law of Superposition)
fossils in the same layer are the same age

Question 14

how is relative dating used in rock layers?

Answer 14

the deeper the strata in sedimentary rock, the older it is (Law of Superposition)
fossils in the same layer are the same age

Question 15

how is relative dating used in index fossils?

Answer 15

index fossils are fossils that are used to compare the age of rock layers at different locations

Question 16

what must an organism be to be used as an index fossil?

Answer 16

• have lived for a short period of time when alive
• be found in many locations
• have been abundant
• be easily identifiable

Question 17

what are 2 examples of index fossils?

Answer 17

trilobites, ammonites

Question 18

What is absolute dating?

Answer 18

any method of determining the actual age of a fossil
* there are different methods, but the most helpful is radioactive dating

Question 19

What is radioactive dating?

Answer 19

scientists working out the age of a fossil by measuring the proportion of the initial and final elements present in the fossil
* scientists know the rate of decay

rocks contain some radioactive elements that decay into a diff. element

Question 20

How does carbon dating work?

Answer 20

• the amount of carbon-12 in an organism stays the same even after death
• by measuring the difference between carbon-12 and carbon-14 in an organism, we can see how long it has been dead for

Question 21

What is the half life of carbon-14?

Answer 21

5730 years

Question 22

Why is carbon dating sometimes not helpful?

Answer 22

it only works for fossils up to about 60,000 years old