Chp 11 - Evidence for Evolution Human Bio

Define fossil

• any preserved remains or trace left by an organism that lived long ago

• Eg: bones, shells, teeth, footprints, faeces, impressions

What do fossils do?

• allow scientists to determine exactly what extinct specifies were like

• Develop picture of life in past

• Build up sequence of evolution of particular plant or animal

What parts would normally be fossilised?

• hard body parts (shell, teeth, bones) bcs take longer to decay

• → chance to fossilise very small bcs decay by micro-organisms

• Must be buried rapidly to be become fossilised (so decomposition slowed or prevented)

How does soil type effect fossilisation?

• wet, acidic soils minerals in bone dissolved no fossilisation occur

• Oxygen deprived acidic soils okay bcs slows decomposition

• Presence of mineral (iron oxide, limestone) deposited in pores of bone & replace organic matter causing petrification

How does the location affect fossilisation?

• quick burial in drifting sand, mud deposits by river, volcanic ash & by other members of species = predators & decomposes don’t remove parts

• Edges of lakes, river system areas = build up sediments during flooding

• Caves = when collapse over bodies (quick burial)

• Volcanically active areas = ash buried body (But normally too hot & destroys body)

• Freezing= subsequent dehydration preserve body

What conditions precept fossilisation?

• soft body parts

• Wet acidic soils minerals = minerals in bone dissolved

• Volcanic rock (igneous & metamorphic) = heat destroy organism

How are fossils discovered?

• chance = erosion

• Excavation likely sites (digs)

How does excavation work?

• slow, painstaking

• Area survey & marked out in sections

• Small hand tools used to remove soil gently = material not destroyed

• Soil sieved = small materials not overlooked

• Photographs taken every step = detail studies of positions of uncovered material carried out later

• Each item labelled & catalogued = prolonged study

• In lab, bones scraped & cleaned, broken parts pieced tgt, measurements ,made & plaster cast/latex mould made