Transcript Radioactive dating

What’s the link?

Two films
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One pure fiction – The Mummy Returns
http://www.youtube.com/watch?v=_GG_nbW1tbU
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One based in fact – 300
http://www.youtube.com/watch?v=0gfZnWVoqZ8
There is a link between the two films that was a major hoax
in 2000
King Xerxes was a King of Persia (now Iran). He
had a daughter called Ruduuna whose coffin
had never been found until………
October 2000
A coffin was found in Pakistan and the
people who found it claimed that it
contained the mummified remains of
Princess Ruduuna.
 They tried to sell it.
 Before they could, it was seized by the
Pakistani police
 How did scientists find out how old it was?
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Carbon Dating
A sample of bone thought to be the
preserved remains of a prehistoric man
was found to have an activity due to
carbon 14 of 50 counts per minute.
 The same mass of living bone would have
an activity of 200 counts per minute.
 The half life of carbon 14 is 5730 years.
 How long has the man been dead?
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Solution
How many times has the activity halved?
 200/2 = 100, 100/2 = 50
 The activity has halved 2 times so two half
lives have passed
 One half life = 5730 years so the man
died 2 x 5730 = 11460 years ago

Dating rocks
Igneous rocks contain radioactive uranium.
 The radioactive uranium atoms decay over
time to form lead atoms that aren’t
radioactive.
 The proportion of uranium to lead in the
rock can tell us how old the rock is.
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Millions of years ago
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The rock only contained radioactive uranium
atoms. In this case, the mass of uranium was
40g
Key
Uranium atom
After one half life
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How many uranium atoms will have
decayed into lead?
Key
Uranium atom
Lead atom
What is the ratio of lead atoms to uranium
atoms?
1:1
What mass of uranium is left?
20g
After two half lives

How many uranium atoms will have
decayed into lead?
Key
Uranium atom
Lead atom
What is the ratio of lead atoms to uranium
atoms?
3:1
What mass of uranium is left?
10g
Learning outcomes
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Grade D: be able to identify materials that
can be dated using carbon dating
Grade C: be able to work out how much
carbon-14 is left in a material using half-life
Grade B: be able to work out how old a
sample is based on activity or mass of carbon
present
Grade A/A*: be able to work out the age of
an igneous rock using the proportion of
uranium to lead present in the rock