Dating a meteorite

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Dating a meteorite (make sure you bring it back
by midnight)
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Hi! Im a Rubidium 87 atom
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I have 37 protons and 50 neutrons
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Im a slightly unstable individual. Theres a
slight chance that one of my neutrons could
change into a proton and an electron a process
called beta decay.
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Then I would turn into a very stable Strontium
87 atom
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There is a fifty-fifty chance that Ill do that
in the next 48.8 billion years.
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Nothing you can do will speed up the
process. Beat me up, heat me itll have no
effect.
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Youll just have to be patient.
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Does anyone know any jokes?
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30 billion years later
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Sr 87
Oooh a change came over me. I feel like a new
atom!
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In a pinhead of Rubidium 87 there are about
100,000,000,000 billion atoms. So at this rate
how many of them will turn into Strontium 87
every day?
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At this rate of decay, nearly three million of us
will turn into Strontium 87 every day.
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A pinhead of Rubidium 87 is just like a clock
ticking at the rate of 3 million ticks a day.
After 48.8 billion years half of the Rb 87 will
have transformed into Sr 87.
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• On 15 July 1878 at 1.45 in the afternoon, this
  25kg lump of rock thudded to the ground in
  Moravia, Czech Republic.
• It was named the Tieschitz meteorite

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• This piece of the Tieschitz meteorite includes
  mineral crystals that contained Rubidium 87 when
  it formed.
• The meteorite also contained Strontium when it
  was formed. Some of this was Sr 86 and some of
  it was Sr 87.

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• As the Rb87 decayed, the Sr87 increased in
  quantity. However the amount of Sr86 would have
  stayed the same.

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• By finding out the ratios of these three isotopes
  it is possible to work out how old a piece of
  rock is.

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Here are 6 isotopes analyses of the Tiechitz. The
first four are from different mineral crystals
and the last two are from mixed samples. Use
this data to clot a graph that will let you find
out how old Tieschitz is.
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Plot of daughter/reference ratios v
parent/reference ratios of Rb-Sr87 decay system
in the Tieschitz meteorite
0.7.30
0.720
daughter/reference ratio Sr 87/Sr86
0.710
0.700
0.690
0.4
0.2
0.3
0.1
0
Parent/Reference ratio Rb87/Sr86
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• As the meteorite gets older, the amount of Rb87
  reduces and the amount of Sr87 increases making
  the line steeper.
• Just for interest, you can also tell the original
  ratio of the two strontium isotopes. This is
  where there was no original rubidium where the
  line crosses the y axis.
• Next you need to find out how steep the line is -
  the gradient.

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Now you can work out how old the meteorite is

• First work out the slope
• Slope y/x 0.0245/0.380
• 0.645
• Now use the slope and the Decay constant for
  Rb/Sr decay ( 1.42x 10-11 yr-1 )
• Age 0.0645/ 1.42x 10-11 yr-1

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• The Tieschitz meteorite is
• 4.54 billion years old!