Answer: Potassium-40 decays into argon gas over time.
Explanation: Potassium-argon dating is a dating method used to determine the age of sedimentary rocks by comparing the proportion of K-40 to Ar-40 in a sample of rock, and knowing the decay rate of K-40.
Potassium-40 undergoes decay following first order kinetics as given below:

Cell-tissue-organ-organ system-organism
Ethanol has been shown to slow down the body's use of fat for fuel by as much as a third, causing more fat to be stored. (or 33%)
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