fossils - unit 4 AOS 2

Question 1

fossil

Answer 1

the preserved remains of a dead organism

Question 2

fossilisation

Answer 2

• an organism dies and is quickly buries in sediment, protecting it from scavengers and oxygen which could cause decay.
• over time, sediment compressed, turining it into rock
• permineralisation occurs where minerals replace the organic material, preserving the organisms remains as a fossil
• techtonic movement and esosion can expose the fossils

Question 3

types of fossils

Answer 3

• trace fossil fossil or structure indicating the presence of organisms, rather than the organisms themselves (e.g. nests, footprints, and burrows)

Question 4

the fossil record

Answer 4

• the information derived from fossils. The fossil
  record is arranged in chronological order and helps us map the history of life on Earth, placing species
  in the appropriate geologic time frame

Question 5

index fossils

Answer 5

• fossils that represent defined geological periods and can be used as reference to easily determine the age of other unknown fossils
• they existed for a short period of time and were widespread geographically
• their presence in a certain strata can provide an indication of the rock layers age.

Question 6

transitional fossils

Answer 6

• fossils that that exhibits traits common to both an ancestral group and its derived descendant group(s) and demonstrate the intermediary evolutionalry stages
• they help to provide evidence of how one species evolved into another

Question 7

relative dating

Answer 7

• a measurement system that uses rock layers to assign comparative ages to fossils
• Fossils are identified as older or younger depending on the strata in which they are found
• the law of fossil succession tells us that sedimentary rock layers develop in chronological order, scientists are able to assign each separate stratum to a particular period of time.

Question 8

absolute dating

Answer 8

• Absolute dating uses the rate of radioisotope decay to determine the exact age of a fossil sample or rock strata
• Radioactive isotopes decay at a constant rate and the time taken for half the original radioisotope to decay is known as the half life
• Different radioisotopes have different half lives and are thus useful for dating different types of fossilised remains

Question 9

using radioisotopes

Answer 9

• Regardless of the radioisotope used, scientists will measure how much of it is present in the fossil versus how much of its breakdown product is present.

Question 10

carbon dating

Answer 10

• When an organism dies, the ratio no longer remains fixed but changes as 14C breaks down into 14N
• Scientists can measure the amount of 14C remaining in a sample to determine how long ago it died

Question 11

other radioisotope methods

Answer 11

1 million to 4.5 billion: uranium to lead

100 000 years +: potassium to argon