Unit 4 AOS 2 - Chapter 10: How we are related

fossil record

info derived from fossils which is arranged chronologically to help map the history of life on earth.

fossil

preserved body, impression or traces of a dead organisms

describe the process of fossilisation

1. remnants of an organism are rapidly covered by sediment, meaning the dead organism is not exposed to oxygen, microorganisms and other disturbances that would increase its rate of decomposition.

2. Sediment layers build upon each other and compact, layer by layer, until pressure cements them together to form sedimentary rock.

3. within this rock, the fossilized remains can take many forms, including permineralized, mold or cast fossils.

Perminieralized Fossils

fossil formed when mineral-rich groundwater deposits minerals into organic material, creating mineral relic.

mould fossil

fossil formed when a living thing decomposes underneath sediment, creating a cavity in the shape of the dead organism

cast fossil

a fossil formed when a mould fossil is filled with sediment.

trace fossil

structures indicting the presence of an organisms rather than the organism themselves.

conditions that increase the likelihood of fossilization:

physical protection from scavengers and decomposers

areas of rapid sediment accumulation

constant cool temperature

low oxygen

low light exposure

law of fossil succession

fossils of same age will be in the same layer of sedimentary rock. Fossils found in lower or higher layers will be older or younger respectively. this is due to sedimentary rock being formed by the accumulation of sedimentary layers on top of each other, meaning older layers are towards the bottom.

relative dating

a dating technique used to determine the relative age of a fossil by comparing its position to other fossils or rock in the surrounding rock strata. - uses law of fossil succession

geological timescales

the law of fossil succession means we do not need to know the age of another fossil but we only need to determine the age of the stratum in which each fossil is found (or the stratum around the fossil)

stratum

a layer of sedimentary rock

index fossil

a group of widespread fossils which existed for a short period and have a known age. Can be used as a reference to easily determine the age of unknown fossils.

qualities of good index fossils

physically distinctive

have had a large population

existed in many geographical areas

only lived within a know, short period of time

transitional fossils:

a fossil that shows traits that are common to both its ancestral group and its descendant group. Important when the descendant species is physically very distinct from the ancestral pieces, such that the fossil can help demonstrate evolutionary changes between the 2.

Absolute dating

a dating technique used to determine the absolute age of a fossil by measuring the relative amounts of radioisotopes to its products

radioisotopes

radioactive atom of a specific element that breaks down over time into more stable products.

3 principles of absolute dating

1. radioisotopes are unstable elements that will break down overtime into more stable products.

2. while radioisotopes can break down at any point, on average the rate of breakdown is constant and can be modelled. One way of modelling htis is by calculating the half-life of that radioisotope

3. half life is the time for half of the mass of the radioisotope sample to break down into predictable and stable products.

radiocarbon dating

a from of absolute dating used to determine the age of a fossil by measuring the properties of a radiocarbon

principals of radiocarbon dating

1. all living things contain carbon and its 2 isotopes (12 and 14) The ratio of these 2 will be the same as in the atmosphere

2. when an organism dies, its carbon 13 will begin to decay and breaks down into 14N. While this decay occurs, the carbon in the dead organisms will not be replaced by existing carbon in the atmosphere. The levels of 12C will remain the same hwile 14C decays at a known rate.

3. at any given point, scientests can measure the amount of 14C present in the fossil and determine ow long ago it died. this is done by comparing the 14C:12C ratio in the fossil to the atmosphere. More long ago an organism has died, the less 14C it will have

homologous structures

featuers present in 2 or more species that may look and function very differently but are derived from a common ancestor

what do homologous structures suggest

evidence of divergent evolution the process in which a common ancestor evolved into 2 or more descendant species.

how do homolgous structures occur

a result of individual populations adapting to different selection pressures or genetic drift

Analagous Structures

features present in 2 or more species that fulfil the same function but do not originate from a common ancestor

what do analogous structures suggest

convergent evolution the process in which distantly related species evolve similar traits overtime due to the action of similar selection pressures.

vestigial structures

features that have lost all or most of its usefulness as a result of evolution by natural seection. Despite having no function, they often remain in species as they are not selected against and are an easy method to infer relatedness

amino acid v dna sequences

limitation to amino acid seqeunces is that closely related species are likely to share similar sequences for certain proteins, thus a more specific comparison is needed requiring dna sequencing.

dna used for more closely related

amino for distantly related