Biogeochemistry

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Biogeochemistry

• Dating (relative/absolute)

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Relative/Absolute dating

• Dating by assemblages of organisms is referred to
  as R D.
• Dating with numerical numbers using radio active
  method referred to as A D.

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• Relative dating ??????? ??????
• ?? ??????? ????????? ?????? ??????? ???????
  ?????????? (??? ? ????? ??????? ? ???). ???
  ??????? ?? ???? ??????? ???? ???? ???????.??????
  ??? ???? ????? ??????? ?? ???? ?? ??? ??? ??? ?
  ??? ?? ???? ???? ?? ??? ???.

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• Absolute dating ??????? ??????? ???????
• ?? ??????? ???? ???? ??? ????? ???? ???? ?????
  ???? ?? ??????. ?????? ???? ??? ??????? ??????
  ?????? ????? ???? ?? ???????? (?????????) ?????
  ????? ?????? ???? ?? ?????. ??? ??? ???????
  ??????? ??? ????? ?????? ??????? ?? ????? ????
  ?????? ??? ???? ? ???? ?????. ????? ???????
  ?????? ???? ????? ?????? ?????? ? ?? ??? ????
  ??????? ??????? ??????? ??????.

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• ????? ?????? ???????? ??????? ?? ???????? ???????
  ??????
• ???? ?????? ??????? ????? ??? ?????? ?? ???????
  ?????? ? ?????????? ? ??????? ?????????? (?????)
  ????? ????? ??? ???? ????? ????.
• ?? ??????? ?????? ??? ??? ????? ????? ???
• ????? ??????? ???? ?????? ??? ???? ??????
• ??????? ?? ??????(parent) ?????
• ???? ??? ?????? ?????? ??? ??????
• (daughter)?????
• Parent element/ Daughter element (U/Pb)??????
  ?????/??????????? (U/Pb)
• ??? ??????? ??? ??? ?????
• Rubidium-Strontium H L(4.7 billion years)
• Uranium-Lead H L(4.5 billion years)
• Potassium-Argon H L(1.3 billion years)

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Problem ??? ???????

• ????? ?????? ???????? ??? ???? ?????? ?? ??????
  ?????? ???? ??????
• Sometimes rocks that are thought to be much older
  than other rocks (because they are buried several
  layers under them) date much younger than the
  rocks found above them!
• Often rocks that are known to be very young
  (because they come from recent volcanoes whose
  eruption date is known) give dates using
  radioactive dating methods that are very old and
  therefore known to be erroneous

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NOW

• Research is not easy interpretation should be
  logic
• It is not a matter of putting your samples in an
  instrument and having the result
• As it has been said earlier result could be
  contradicting

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C14

• Carbon atom weighs 12 atomic mass units.
• One in every trillion carbon atoms (in earth
  atmosphere TODAY) weighs 14 atomic unit.
• C14 is a radioactive atom
• Half of the C14 will decay in about 5730 years
  from the time it was formed to form Nitrogen
  (and half of the reminder will decay into N in
  another 5730 years and so on)

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• N.B Carbon dating used on organic material (not
  on rocks or even fossils), C14 not used for
  dating on anything considered to be older than
  50000 years.
• When N in the earths upper atmosphere is struck
  by cosmic radiation it turns into C14
• N(14) C(14)
• Most C14 quickly will combines with oxygen to
  form radioactive CO2
• plant absorb CO2 (small amount will be
  C(radioactive)O2 C(14)O2)

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• Feeding on plants animals will take than some of
  the C14 in their bodies
• When animal and plant die they stop absorbing C14
  and this C14 will slowly decay into nitrogen
• By measuring the amount left in the dead animals
  and with some assumption scientist could
  determine the date of the animal death.

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Assumptions Made in Radiocarbon Dating

• 1-A constant rate of decay - i.e. the half-life
  of carbon-14 has always been 5,730 years
• 2-No loss or gain of parent or daughter - i.e.
  the specimen being dated has not taken in or lost
  any carbon-14 since the time it died (e.g through
  contamination).

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• 3- Known amounts of daughter at the start. This
  requires that the following things be true
•        The ratio of carbon-14 to carbon-12 that
  exists in the earths atmosphere today has always
  been the same. Has it always been the same?
•        The ratio of carbon-14 to carbon-12 that
  exists in all living things always matches  the
  ratio that exists in the earths atmosphere. Does
  it?

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