Chapter 11 - Fossils

fossils

preserved trace left by organisms

fossil formation

rapid burial of dead organisms in suitable conditions slow down decomposition, leading to fossil formation

rapid burial

• fossils of human ancestors often found in places where rapid burial can occur

• EG: caves, volcanically active areas

• limeatone found in caves consist of calcium carbonate, so chemical deposits around dead organisms or cave will collapse covering animal bodies

importance of fossil record

• provide physical evidence of past species

• allow scientist to create evolutionary links

• indicates increase in complexity and diversity of species

active sedimentation sites(help in rapid burial)

• drifting sand

• mud deposited by river

• volcanic ash

effect of soil type on fossilization

• we acidic soil

• alkaline soil

wet acidic soil

• minerals in bone dissolved, no fossilization occurs

• no oxygen in peats(wetland), complete preservation of soft tissues and bones may occur

alkaline soil

• produces best bone fossils because minerals in bone not dissolved

• new minerals(lime or iron oxide) are deposited into pores of the bone, replacing organic material

• thus, bone become petrified(turn into rock) while details of structure still preserved

types of fossilization

• fully preserved organisms

• hard parts remaining

• moulds

• casts

• petrification

• trace fossils

fully preserved organism

entire body preserved, including soft tissues

hard parts remaining

soft body parts decay, leaving only bones, teeth, shells

moulds

organism body leave an impression, the cavity it made may form mould

cast

mould cavities filled with minerals

petrification

when minerals enter tissue of dead organism and replace them, turning organism to stone

trace fossil

details preserved in rocks that are an indirect evidence of life

discovery of fossils

• found by chance at ground surface because they got uncovered by erosion

• usually due to slow, careful excavation/digging on likely sites

• when human ancestor fossils found, artefacts usually found in association

artefacts

• objects deliberately made by humans

• EG: stone tools, carvings