fossils

why study fossils for evolution?

One of the crucial pieces of evidence for evolution, the gradual change in the charactersitics of organisms over time. Is the record of those changes left to us in the form of fossils

What do fossils allow us to determine

Allows us to determine exactly what an extinct species were like.

What is a fossil

Any preserved trace left by an organism that lived long ago. A fossil does not have to part of an organism.

what have fossil records allowed scientist to do (non-human)

There are many cases where fossil records have allowed scientists to build up a sequence of evolution of a particular plant or animal. 

Examples of fossils

• Footprints

• Bones

• Teeth

• Impressions of all or part of an organism

• Faeces (Coprolites)

Name and describe the main types of fossils

• Index fossil - widely distributed fossils, which existed only for a short time period {which is known}, useful for dating rocks in which they are found. {If another fossil is found in the same layer of rock, then existed at the same time}

• Mould - a hardened impression (hollow) that has been made in sediments

• Cast - occurs when a mould fossil is filled with minerals and allowed to harden {can use to examine anatomy}

• Mineralised fossils - waterborne minerals fill the void spaces within the original material of the specimen. The original organic material of a specimen is replaced by minerals.

Features of Index Fossil and why they are necessary

Feature of Index Fossil	Why this feature is necessary to meet index fossil requirements
Widespread	To allow dating worldwide or at a wide range of locations
Found in large numbers	Numerous enough to easily find. Increased chance of discovery
Recognisable	Easily distinguishable and identifiable
Lived for a limited/short/know period of time	Easily dated (time period of existence) easily identified. Can be used to find an accurate relative age of other fossils

Parts of organism likely to form fossil & why:

When an organism dies it is decayed by micro-organisms. This processes rarely leaves behind traces of their existence. 

Commonly, hard tissues, such as shell or bone, are fossilised. 

It is rare that soft tissues are preserved. 

What must occur in order for fossils to form

the process of decay and decomposition must be slowed. This can occur when organisms are buried rapidly.

Ways in organisms are rapidly buried:

•Drifting sand

•Mud deposited by rivers

•Volcanic ash

•Other members of the same species (more recent occurrence) {spiritual reasons of burial}

circumstances of location most favourable for fossil formation

• Organisms that die in water, not on land are more likely to be buried quickly by sediment and less likely to be destroyed by scavengers or erosion.

• Low energy environments (a lake or swamp) are also favorable as remains are less likely to be destroyed by mechanical processes.

How do conditions of soil impact fossil formation

• If wet, acidic soil containing oxygen → dissolve the minerals in the bones → no fossiliation

• Soils containing no oxygen (fine sediment) and usually low temperatures {could be snow} (Peat) → complete preservation of tissues (some bones can also survive)

• Alkaline soils → do not dissolve minerals → fossilation occurs (Bones). Additionally new minerals such as lime or iron oxide are deposited into the pores of the bone → petrified (turned into rock)

conditions necessary for fossil formation:

• Soil type - alkaline with low oxygen levels

• Specimen to be fossilised - contains hard (solid) parts/bone/teeth

• Micro-organisms - Not present/ protected from decay

• Exposure to atmosphere - Covered quickly at death/protected by sediment

what is the main way fossils are discovered?

excavation. site suveryed, marked into sections, use small hand tools to remove small samples

What is an artefact? Define & provide examples

Objects that have deliberately made by humans. Stone tools, beads, carvings, charcoal from cooking fires, cave paintings.

Why does fossil reconstructions lead to controversy

Reconstructions are approximations based on the experience of the scientists involved.

Where are fossils of human ancestors commonly found? Name & explain

• Edges of ancient lakes or river systems - these areas built up sediments when flooding occurs or when water flows rapidly

• Caves - many caves are in limestone (consists of calcium carbonate) which is deposited around dead organisms when roofs or walls collapse (rapid burial)

• Volcanically active areas - whilst it is unusualy for fossilisation to occur near volcanic eruptions (due to the heat), fossils have been discovered in East Africa which have been preserved by falling ash

What is the fossil record?

the evidence provided by fossils of the development of life

why is the fossil record incomplete?

• only a very small number of organisms are fossilised

• few fossils have been found

what are the problems with the fossil record

• fossilation is a rare, chance occurence

• The 4 conditions must be met - quick burial, prescence of hard body parts, absence of decay organisms, left undisturbed - long periods of stability

• Must be discovered (may be inaccessible of may have been destroyed). The fossil record is incomplete

• Classification of species may require many fossils to have been discovered and studied

• Dating fossils can be difficult

• Fossils are not often whole organims and must be reconstructed

• Scientists interpretation of the findings/ evidence may differ

• Many fossils are destroyed by geological processes/human activity

reasons why gaps in the fossil record exist

• fossil can be destroyed through human activity/geological processes/weathering and erosion

• fossil may not be discovered as people are not looking in thr right locations or they are not being recognised.