Upon examining layer m, you find that it contains a small proportion of the radioactive isotope - potassium-40, which decays into argon-40 with a half-life of 1.3 billion years. assuming no contamination, what would be the age of a this layer if it contained 25% of potassium-40 and 75% argon-40?

t = 2.6 billion years

Explanation:

If potassium becomes 25% of its initial value

so we can say it becomes half two times

as we know that 25% means it is 1/4 times of initial value

so we will have

here we know that

t = 2.6 billion years

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in this image, you can see solar radiation going through ocean water.

no image, but probably absorption