Dating fossils

what is dating fossils?

happens after excavation of fossils or artefacts to determine the age of. the material

why is knowing the age of fossils important?

it is crucial win finding out the sequence of changes that have resulted in present day humans

what can methods of dating provide (like what are the two types of dating)?

absolute and relative dating

what is absolute dating?

the actual age of the specimen in years

what is relative dating?

a comparison of fossils to tell us whether a sample is older or younger than another.

modern technology has enabled accurate…

estimates to be made of the absolute age of. many samples

when the absolute age of samples cannot be taken..

knowing weather one fossil is older to younger is important (therefore can understand the sequence of history on earth)

how are the age (or date) of fossils expressed?

is given in years before present time e.g 45000 years BP is 45000 years old

what is one of the most abundant elements in the earths crust?

potassium, therefore it is found in most rocks

what is the potassium argon dating method based on?

the decay of radioactive potassium to calcium and argon

what are isotopes?

they are atoms of the same element but a different number of neutrons

which are the stable and which is the radioactive potassium isoltope?

K 39 and K 41 are both stable with 20 and 22 neutrons respectively. but K 40 is radioactive and has 21 neutrons in nucleus.

describe how K 40 decays.

it decays to form Ca 40 and Ar 40 at a slow, but consistent rate.

describe how the potassium/ argon dating works please 🙂

by determining the relative proportions of K 40 and Ar 40 in a rock allows the age of the rock to be calculated.

what happens to the proportion do K40 and Ar 40 in a rock sample as the rock ages

the portion of K40 decreases as the amount of Ar40 increases

describe what ‘half life’ means?

it is the time it takes for the amount of a substance to half

what is the half like of K 40? (how much time does it take for the amount of K40 to half)

1.25 billion years (1.25 × 10^9). therefore after 100,000 years only 0.0053% of K40 of rock would be covered to Ar40 (therefore not very accurate)

potassium argon dating is not very accurate on smaller scales, when is it most useful?

in samples over 200 000 years old.

what are the limitations of potassium/. argon dating?

not al rock types are suitable, and can only date rocks over 100,000-200,000 years old

what must be available to potassium/ argon dating method to work?

some suitable rock of the same age of the fossil must be available. the age of the rock is determined using K/Ar dating, and hence the age of the fossil is inferred.

what is an instance where K/Ar dating method can be used?

when rocks are produced in volcanic eruptions and they burry bones (therefore the rock which is the same age as the fossil can be tested)

how many years is two half lives of K and what is the resulting fraction of isotope K40 and Ar?

2.5 billion years 25% of rock sample is K40 and 75% is Ar

what is another name for carbon 14 dating?

radiocarbon dating

what is carbon14 dating based off of?

based on the radioactive decay of carbon 14 isotope to nitrogen.

is carbon 14 dating absolute or relative?

absolue

Is K40/ Ar. dating absolute or relative?

absolute

all living things contain which element?

carbon.

how do all living things contain carbon?

via the food chain. the plants get it from CO2 in the atmosphere, animals get it via the rest if the food chain

what is the most stable and abundant isotope?

the carbon 12 isotope

where is. carbon 14 produced?

in the upper atmosphere by the action of cosmic radiation on nitrogen at about the same rate it decays

how is carbon 14 intergrated into organisms?

the carbon 14 is taken. up by plants during photosynthesus, this passes along the food chain, becomes part of living tissues.

what happens to the carbon 14 in an organism after death?

after death, the intake ceases (of carbon) and C14 decays into N at a fixed rate.

what is the ratio of C14 (radioactive) to C12 (stable atoms)

1 C14 atom to every million, million (10^12) atoms of C12

how does C14 dating work?

by measuring the amount of radiation liberated by a sample, the ratio of C14 to C12 can be estimated, and the age of the sample can be calculated

what is the ratio of radioactive carbon in the tissues if living organisms today?

1 atom of C 14 to 10^12 atoms of C 12

what is the half life of C14(before it decays to N)

5730 years (±40 years)

using the normal method of C14 dating how much of the sample needs to be tested?

at least 3g of organic material, so that the rate of radioactive decay of C14 can be measured.

what is the most refined technique for C14 dating?

accelerator mass spectrometry (AMS) radiocarbon dating

what is accelorator mass spectrometry (AMS) radiocarbon dating?

this is a tequniwue that involves breaking the sample up into atoms so the number of atoms in each isotope of carbon can be counted

why is accelerator. mass spectrometry radiocarbon dating favoured than normal radiocarbon dating

smaller masses of samples as small as 100 micrograms can be used (0.0001g) compared to the 3g needed for normal

what has been able to be dated wuth t he accelerator mass spectrometry radiocarbon dating?

is able to date cave paintings from tiny samples of. pigment. there have been pigments that contain organic material e.g charcoal, while honey, milk, blood, oil seed was used to bind the particle together

what are the limitations of accelerator mass spectrometry radiocarbon dating?

after 70,000 years the % of C14 is 0.021% (therefore is too small to be measured accurately), the material must contain organic compounds (living things that contain carbon), it was prior assumed that the ratio of C14 to C. 12 was constant, but now we know that the amount of C 14 in atmosphere varies (therfore radiocarbon dates must be treated with a certain degree of caution)

what is t he furthest C14 dating can be measured accurately?

approx 60, 000 years

what are the advantages of accelerator mass spectrometry radiocarbon dating?

dates of fossils of more recent origins are able to be dated, also artefacts that are found in association with charcoal (from cooking fires) can be deduced.

is tree ring relative or absolute dating?

it is absolute.

what is another name for tree ring dating?

dendrochronology

what is tree ring dating?

trees grow concentric rings, each ring being one year of growth, creating a timeline in the tree trunk. you can match years by counting the rings and comparing one sample to another.

what changes the width of the tree rings?

the differences in width of the tree rings is according to how good the growing season is with water etc…

what are the limitations of tree dating?

the timers only rarely preserved long enoguh to do long dating, it depends on having a continuous sucession on nearby timber.

how long back can tree dating go back?

5600 years

can can tree ring dating be used to verify?

carbon 14 dating

tree ring dating is useful so we can…

backtrack using comparisons

each method of absolute dating is…

limited in its application because each depends on a particular set of circumstances before it can be used.

corrections for the fluctuations in C14 content in atmosphere can now be possible for about how many years back and why?

for the past 9000 years, by other information such as tree ring dating.

when is relative dating used?

when it is not possible to determine the actual age of the fossil or artefact

what does relative dating establish?

a sequence of events, scientists determine whether sample is older or younger than another sample (e.g a rock or soil in which it was found)

what are some examples of relative dating?

fluorine dating and stratography

what is stratigraphy?

is the study of layers or strata

what are the three main concepts of stratigrpahy?

principle of superstition, correlation of rock strata, and index fossils, (fossil pollen grain analysis can also help confirm this data)

wh is the principle of superposition?

it assumes that in layers of sedimentary rock the layers at the top are younger than those beneath them. thus any fossils or other material found in the top layer ill be younger than material found later down.

why should principle of superposition be handled with care?

because distortions of the Earths crust do occur, sequence of rock layers may be turned upside down. Also it is possible for fossils/ artefacts to be burried by animals/ early humans sometime after deposition of the sediment. therefore the spcimen may be younger than some layers above it

what is correlation to rock strata

it involves maintaining different rock from different areas.

how can correlation of rock strata be done?

matching strata can be done by examining the rock itself and studying the fossils it contains. rocks that contain the same fossils may be assumed to be the same age.

what can we do with the data from correlation rock strata?

rock strata from different areas have similar layer sequences , we can line up (correlate) these sequences to provide a sequence of layers from oldest to youngest.

what are some problems with correlation rock strata?

sometimes layers are missing, sediments may have been eroded and then other sediments may be redeposited, one type of sediment. may not be as widespread (although we ca still correlate using similar layers)

what are index fossils?

they are fossils of great value n stratigraphy, they are widely distributed, and were only present on earth for a short period of time. these make relative dating of strata more precise

fossils may be used to compare strata from different localities often…

hundreds or thousands of years apart.

what is fossil pollen grain analysis?

some fossil pollen grains are useful as index fossils but, even if they cannot be used in this way (if a planet was widespread for a short period of time) the presence of preserved pollen grains in a soil or rock sample can enable a botanist to construct a picture of type and amount of vegetation existing at the time of deposit. we can them infer about the climate. this data can be used to confirm relative dates by other methods

pollen produced by flowering plants is…

unique to each species of plant

what is fluorine dating?

is used for relative dating of fossil bones in the same location. if bone is left in the soil fluorine ions from the ground water replace some of the ions in the bone over time. All fossil bones in a particular deposit should contain same amount of fluorine.Older fossils. have been there longer and therefore have more fluorine.

why is fluorine dating useful in stratigraphy?

as you can detect fossils that have been displaced.

why can’t you absolute date for fluorine dating?

can’t use absolute date though as the amount of fluorine in water supply fluctuates over time.

why is the fossil record very incomplete?

as conditions for fossilisation do to always occur or they occur at irregular periods of time.

what are some problems with the fossil. record.?

certain conditions must be met

what are the conditions that must be met for a fossil to be formed?

there must be a quick burial of material, presence of hard body parts (e.g bones, teeth, shells, exoskeletons) absence of decay organisms, long period of stability, organism must be left undisturbed.

fossilisation is a … occurrence and there are many… in records because…

chance occurrence and there are many gaps in records because fossils have not been preserved.

what are the. reasons for incomplete fossil records?

only a very small population have been discovered, some are too deep in the ground or are in inaccessible places, not been recognised as fossils, or have been inadvertently been destroyed. e.g by agriculture or industry.

why can finding and dating fossil material be problematic?

to use carbon dating, material must contain carbon and date past 60,000 years, age of fossil determined. in the sediments in which it was found (potassium/ argon dating relies on suitable material e.g volcanic lava being present), it is unusual to find fossil of entire organism/ whole skeleton of organism (particularly for human ancestors there is often just a sew fragments of bone)

by do some scientists disagree with fossil reconstructions?

as human ancestors usually only have a few fragments of bone, scientists have to reconstruct what the organism would have looked like. these experts estimate shape of the face and upper jaw in order to complete reconstruction, some reconstructions are only approximations based on experience of scientists involved. some scientists disagree with interpretations leading to controversy

what is the resotuktion to the controversy of reconstructions to fossils

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