The decay of potassium-40 to argon-40 explains why there is so much argon in the atmosphere, compared with the other noble gases.Almost all atmospheric argon (99.6%) is argon-40, whereas the argon in the Sun and stars, produced by stellar nucleosynthesis, is mostly argon-36.Of this, only 0.012% (.00012) is radioactive potassium-40.Thus, the crustal abundance of potassium-40 is: 0.012 x 0.00012 = 1.4 x 10] = 19 parts per million potassium-40 when the Earth formed Shortly after the Earth formed, the abundance of potassium-40 was 19 parts per million. That means that 17.6 parts per million of the crust, in the form of potassium-40, has decayed away over the past 4.5 billion years.
The proportionality is related to the probability or “. Or if the rock is subject to atmospheric conditions, the argon gas will mostly flow out of the rock and one can account for the presence of atmospheric argon gas in the rock.
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Note: The calculations have a precision of two significant digits.
Your answers might be slightly different due to rounding.