fossils

fossils

preserved remains/impression/traces of an old/ancient/extinct organism. This could be footprints, burrows, faeces, impressions of plant or animals, bones, shells or teeth

fossilisation steps

Death and decay- soft body parts are decomposed/scavenged leaving only hard body remains

deposition - the hard remains are rapidly covered with silt, clay, mud, and sand, over time layers build up

Permineralisation- pressure from covering layers of dirt/rock cause the hard organic material to be replaced by minerals

Erosion/exposure- movement of earth plates may displace the fossil and return it to the surface for discovery.

factors affecting

Type of organism- plants- petrified rock is fossilised plant material dissolved salts replace plant tissue.

Soil pH- high phalkaline soil conditions, anoxic (low oxygen) conditions like peat or limestone to protect against oxygen damage and prevent decomposition by saprotrophs( obtain nutirents by eating decay)

Mineral content of soil- high pressure to promote mineralisations,

Weathering- temperature could enough a fossil may be formed when the organism freezes rather than decomposing, due to being dehydrated and preserved

Erosion - only limited amount can occur to not destroy the fossil/organisms. Only for exposure

Time taken to become buried, environment, chemical destruction, mechanical destruction, biological destruction

factors affecting pt2

1. Time taken to become buried

2. Environment - some rock does not form fossils, sedimentation is necessary for fossils

3. Chemical destruction : soil pH, preservation of oxygen

4. Mechanical destruction : weathering and erosion, trampling by animals

5. Biological destruction : presence if microorganisms such as bacteria or fungi. Carrion may take away parts of the organism

6. pH - low pH (acidic envrionment) conditions can dissolve the minerals that form fossils, destroying them in the process.

fossil evidence

Shows past life/extinct organisms, shows the similarities and differences between them

Show that life/environment has changed over time or that life on earth has a long history

Show how one type of organism/structure has transitioned to another

Show us if the organism has developed into homologous or analogous structures- comparative

Evolution and common ancestor

Dating of strata

Identification of new species

fossil evidence pt2

Fossils give us an insight into past life forms

Fossils show the patterns and speed of evolutionary change through gradualism and punctuated equilibrium

Gradualism - evolution occurs as a steady, slow divergence lineages at an even pace -

Theory suggests that sudden bursts of evolution are an illusion

 punctuated equilibrium - states that species will remain stable for long periods of time but may then quickly change into new species due to a rapid change in the environment.

• Shows us the record of species over time

• Gives scientists an understanding of similarities and differenced between current and extinct species demonstrating change. 

• The distribution of fossils over different continents supports the idea of evolution.

limitation of fossil record

Fossil record provides evidence of extinct organisms. That change has occurred in species and in groups of species over a long peroid of time is evidence by fossils, as well as by the progression of simple to more complex organisms in the fossil record.

Fossil record is total number of fossils discovered and gained information from

Geologic time scale is a system of chronological measurement that describes the timing and relationships between events that have occurred throughout earths history

Fossil record

• Looks (shape, size, ect)

• Where or how they lived

• What other organisms they lived with

• Transitional forms

Fossil record is incomplete:

• Only hard parts are likely to form fossils or soft parts are unlikely to form fossils

• Only organisms that avoid decomposition/scavengers/predators for fossils or fossils only form in areas with no oxygen/bacteria

• Only orgnaisms that are buried in sediment/mineral rich water form fossils or rapid burial

• Not all fossils have been found yet

• Some fossils have been destroyed (volcanic eruptions/human activates/earthquakes)

• Not all fossils can be found (too far underground/underwater)

Not all organisms represented

Taxonomic bias- not all fossils have been discovered some organisms may not be represented or other over represented

Undiscovered fossils- older fossils are more difficult to fine. Plate tectonic processes have destroyed or displace fossils

Geographic bias-not all areas produce fossils,

rainforests teeming with life and in a hot and moist climate are also poor places for fossils to form as a carcass can decay quickly and not have time to be buried. Similarly a rocky mountaintop is a poor place for fossils to form with no fine sediments being laid down