8.3 evidence from fossils

evidence that can be obtained from fossils

• changes that have occurred in the types of organisms living on this planet

• supports the theory of evolution

ways the fossil record can be interpreted

• time scale represents millions of years

• species that are further down on the record are older

faunal succession

the principle that fossilised flora and fauna in sedimentary rock strata are arranged vertically in a specific order

index fossils

fossils with known ages that can be used to relatively date other fossils by comparison

must be distinctive, abundant, distributed worldwide and have existed for only a short period of time

transitional fossils

shows traits of both its ancestral group and its descendants, acting as evidence of an intermediate form

two main ways of dating fossils

absolute age: a precise, numerical age of a fossil

relative age: a comparative age of a fossil in relation to other fossils

process of relative dating

stratigraphic method

• determining relative age by its position within rock strata

use of index fossils

process of absolute dating

radiometric dating that depends on the known rate of decay of a radioactive parent isotope to a stable daughter product, measured in half-lives (eg. carbon dating)

carbon dating

• carbon 14 (parent isotope)

• nitrogen 14 (daughter product)

• 5730 years half life

• dating organic remains

• only used for ages up to 50,000-60,000 years