11.1 Fossils

what is a fossil

• a preserved trace left by an organism that lived long ago.

• examples include bone, teeth, shells, footprints

why are fossils important

They allow scientists to determine what extinct species look like

• Other material associated with bones (i.e the rock they were found in, fossils of other plants/animals) help develop a picture of life in the past

• What did the organisms eat?

• What other organisms existed at the same time?

• What was the climate like at the time?

• Fossil records can help build a sequence of the evolution of a particular plant or animal

what is the fossil record

the record of the occurrence and evolution of living organisms through geological time as inferred from fossils.

how is the fossil record evidence for evolution.

• Establishes evolutionary links between species (shows common ancestry)

• Provides evidence of which organisms lived on Earth in the past

• Provides examples of organisms which may now be extinct

• Provides examples of transitional organisms between species

how are fossils formed

Fossilisation can occur if buried by drifting sand, mud deposited by rivers, volcanic ash or buried rapidly by others of it’s species slowing the decay process

effect of soil on fossilisation

TIP #5: Soil conditions: An alkaline soil environment favours the preservation of bone as new minerals are deposited into the pores of bones (petrified).

TIP #6: An acidic environment favours the preservation of soft tissues and bone, provided it doesn’t contain any oxygen and is at a low temperature (ie. peat), complete preservation can occur.

location of fossils

• fossils of human ancestors often found at edges of ancient lakes and river systems or in volcanically active areas

• this is because the organism can be bruied rapidly, preventing decomposition

summary of ideal conditions for a fossil to form

• Sediment/soil is alkaline with low oxygen levels

• Sediment/soil has low pH/acidic with no oxygen

• Organism protected from decay by microorganisms

• Body undisturbed by scavengers

• Body undisturbed by geological processes (e.g. weathering, erosion)

• Rapid burial

• Body is undisturbed for a long period of time (so that fossilisation can occur)

• Remember: most fossils are of hard parts of body (teeth, bones) not soft part (e.g. tissues) as they are not as easily destroyed

how do the discovery of fossils occur

• Chance surface discovery due to erosion

• Excavation

• Area surveyed & marked in sections

• Small hand tools used

• Any soil removed is sieved so very small fragments are not overlooked

• Artefacts are usually found in association with human fossils

• Photographs of every stage of dig to study detail of positions of uncovered materials

•fossils and artefacts are labeled and catalogued

• After excavation

• In the lab fossil bones are scraped clean, broken parts put together, measurements taken

•P laster casts or latex molds may be made

what are artefacts

• Artefacts: Any objects made by humans e.g. weapons/tools, beads, carvings, paintings

why are there few fossils and gaps in the fossil record

• Buried too deep to be found

• Located in places that are not possible to get to

• Fossils may have become exposed but were then weathered or eroded

• Destroyed by geological processes/events (e.g. earthquakes, volcanic eruptions)

• Destroyed by human activity (mines, urbanisation ect.)

• Fossils may not be recognised as fossils

• May not be looking in the right places

• When discovered scientist may disagree on the interpretation of fossils

• May not be able to date some fossils that are found due to limitations in dating methods