Evolution

fossils

any preserved remains of a once living organism→ allows scientists to build a sequence of evolution for a particular organism

Fossil types

Petrified, mould and cast, trace, carbon film and preserved remains

petrified

turn to stone, fully dissolved minerals in water seeps through layers of sediment and hardens when evaporated

mould and cast

mould is the hard part, cast is result of mould and fills empty space of mould

trace

shows activity of an organism, sediment becomes solid rock *no water allowed

carbon film

organism dies and buried in sediment, material that makes organism breaks down and carbon remains, thin layer can show a print

preserved remains

whole organism is preserved, amber, tar or ice

amber

organism trapped in trees sticky resin and dies, more resin covers sealing insect inside

tar

organism is trapped in tar pit and dies, tar soaked into bones and stops bones from decaying

ice

organism dies in cold region, body frozen in ice which preserves organism, even hair

fossil formation

buried by sand, mud and volcanic ash or other members of species, buried rapidly or conditions not ideal for decay then decomposition is slowed

not favourable conditions for fossilisation

wet, acidic soils dissolve minerals in bone, therefore no fossil formed

favourable conditions

soils with no oxygen (peat) result in complete preservation of soft tissue and bone, alkaline soils, new minerals in soil deposit in pores of bones

stages of fossilisation

1. death and decay, 2. deposition, 3. permineralisation, 4. erosion/exposure

discovery of fossils

erosion, earth movements and excavation can expose fossils and artefacts (made by humans)

absolute dating