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Topic: half life & potassium 40  (Read 16885 times)

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Maude79

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half life & potassium 40
« on: December 10, 2011, 02:20:37 AM »
The half-life of 40K (potassium 40) is 1.25 billion years.?
If a rock that formed just before the beginning of the Proterozoic Eon (2,500,000,000 years ago) originally contained 200gm of 40K, about how much would be left in the rock today?

UG

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Re: half life & potassium 40
« Reply #1 on: December 10, 2011, 05:21:43 AM »
If a rock that formed just before the beginning of the Proterozoic Eon (2,500,000,000 years ago) originally contained 200gm of 40K, about how much would be left in the rock today?
How many half lives of 40-K is 2,500,000,000 years?
The answer to the above is how many times do you need to halve 200 g to get the answer.

vmelkon

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Re: half life & potassium 40
« Reply #2 on: December 17, 2011, 12:52:36 PM »
Apply the standard equation
result = m * 0.5^time/half-life

result = 200 g * 0.25