evidence for evolution Flashcards
what are fossils
Remains or print of organisms in rocks
Show previously living forms of species
what are the conditions required for fossilation
protected and preserved
• Buried quickly
• Prescence of hard body parts
• Absence of decay organisms
• Long period of stability – left undisturbed
Soil type: Wet acidic soils dissolve the minerals n the bone so fossilation can’t occur
However, if the acidic soil doesn’t contain any oxygen (peat bogs) complete preservation of the soft tissues as well as bones can occur
Alkaline soils form the best fossils as the minerals in bone don’t dissolve
New minerals such as iron oxide or lime are deposited in the pores of the bone, replacing the organic matter
The bone becomes petrified but details are details are preserved.
explain the process of fossilation
- Process in which plants or bones turn into stone
- In each stage information and specimens are lost
- Mortal remains start to decompose, soft tissues
disappear quickly through bacteria
The bones can be mineralised or crystallised and eventually the bones transform to stone.
The hard parts such as teeth and bones can remain undamaged but they eventually disintegrate when they’re still in contact with the air
If they are covered, they won’t disintegrate
Over time more layers are deposited over the remains
Over time rock formations can be raised of turned over and the fossilised bones can come to the surface, which is caused by erosion.
what are the 2 types of fossil dating
relative dating
absolute dating
what is relative dating? list the 3 types
Ages fossils by comparing the fossil with other known fossils
The age that is reached is relative to the age of another fossil
- stratigraphy
- index fossils
- pollen analysis
what is stratigraphy in fossil dating
Places fossils in a sequence by noting their position in strata (layers of rock)
The principle of superposition: fossils found in lower strata were deposited first and are older
Limitations: earth movement, erosion, fossils are dig up and buried, layers weren’t deposited horizontally to begin with
what are index fossils in fossil dating
Fossils that are particularly useful for stratigraphic dating
Used to compare the age of strata at different locations around the world
Criteria: distinct and easily recognisable structure, widespread, alive for a relatively short period of time
E.g. if the same index fossil is found in Australia and Africa, we can assume the strata layers on each continent to be the same.
what is carbon-14 and how does it form in radiocarbon dating
radioactive carbon isotope
forms when nitrogen in the atmosphere is hit by gamma rays, turning one of the protons into a neutron
now has 6 protons and 8 neutrons from 7 and 7. It is now a carbon-14 isotope
Radiocarbon joins with oxygen to form carbon dioxide
Plants take this in through photosynthesis and it becomes part of the body structure
moves through the food chain by being eaten by other organisms.
what is radiocarbon dating
uses the radioactive carbon-14 in fossils.
When an organism dies, carbon-14 in the tissues decays at a fixed rate
Over a period of 5730 years half of the original quantity of carbon-14 would have broken down – half life
When an organism dies the C-14 that has been taken in during the life times decay
The amount of C-14 is assumed (using a known substance from today) and compared with remaining C-14 in the fossil.
By measuring the amount of radiation given off by a sample and by knowing the decay rate of C-14, the ratio of carbon-14 to carbon-12 in the atmosphere can be estimated and an age can be calculated
The older the fossil the less C-14
what are the limitations of carbon dating
Fossils must be of at least 3g of organic material
Dates back to 70 000 years
Ratio of C-14:C-12 is not constant and results must be cross referenced with measurements from tree-ring dating samples
list some characteristics shared by primates
Pentadactyl – five fingers/toes
Reproduction not restricted to a breeding season
Large and complex brain
Vision: Forward facing eyes for 3-d vision, stereoscopic and colour vision
Grasping fingers and toes with friction ridges (fingerprints) for gripping
describe some trends in primate digits as evolution progresses
Increasing mobility and ability to move digits independently
First digit opposable (except human foot)
First digit increases in length
Increased precision grip
Claws give way to nails
Pads in fingertips develop
describe some trends in primate dentition as evolution progresses
Reduction in number of teeth
4 cusped molars to 5 cusp molars
Monkeys and apes have large projecting canines with diastema (space separating teeth of different function)
describe some trends in primate olfaction as evolution progresses
Reduction in olfaction
Reduction in snout length
Reduced prognathic jaw (jutting jaw)
Increasingly flat face
describe some trends in primate vision as evolution progresses
Increasingly forward-facing eyes (stereoscopic vision)
Increases 3d vision but decreasing field of view
Increase efficiency of eyes
Increase in bony sockets
Increased visual area in the brain
describe some trends in primate brains as evolution progresses
Increase in size (in proportion to body size)
Increased convolutions
Increased cerebral cortex size (high order functioning)
Allows for greater development of skills
describe some trends in primate gestation and development as evolution progresses
Not restricted to breeding seasons
One offspring at a time
Long gestation
Immature at birth therefore increasing length of time that the offspring are dependent on the parents and increased learning
Increasing later arrival at sexual maturity
explain what potassium argon dating is
Only technique that can be used for dating very old archaeological materials
Potassium can either turn into calcium or argon
One of the protons in K-40 is hit with a gamma ray, creating Argon-40 gas
K-40 has a half-life of 1.25 billion years
By comparing the proportion of K-40 to Ar-40 in volcanic rock and knowing the decay rate of K-40, we can determine the date of formation.
How do K-Ar gasses get into volcanic rock?
When rocks are heated to melting point, Ar in them is released
When rock recrystallises it becomes impermeable to the gasses
As K-40 in rock decays into Ar-40, gas is trapped in rock
Measuring ratio of K:AR you can age the rock
What are the limitations to potassium argon dating
Works for igneous (volcanic) but not sedimentary rock
Accurate from 4.3 billion years to 100 000 years ago, as only 0.0053% of K-40 in a rock will have decayed by then and pushes the limits of current detecting devices.
give an example of comparative anatomy
All tetrapod’s share a common limb structure: single upper bone, 2 lower limb bones and five digits.
The structural pattern can be detected in the ancestral tetrapod and is present in the limbs of nearly al amphibians, reptiles, birds or mammals regardless of whether the limb is a hand, hoof, wing of flipper.
list some locations where fossils can be discovered
Edges of ancient lakes and river systems (build up sediment when flooding)
Caves (limestone environment)
Volcanically active areas (buried rapidly under ash)
why are there gaps in the fossil record
large amount of undiscovered fossils which are buried too deep
fossils have been dug up and disturbed by other organisms
fossils have been destroyed in human construction and building sites
what are hominins
group of modern and extinct human species and all immediate ancestors
