Question

suppose a rock's chemical composition is analyzed and is found to contain 5x more potassium atoms than argon atoms. When did the rock form?
(10 million, 100 million, 500 million, 2 billion, or 4.5 billion years ago.)

Answer 1

the potassium-argon dating cycle is more complex than carbon-14

from "hyperphysics" ... t = 1.804E9 ln[9.540(Ar/K) + 1]

Answer 2

the K and Ar atoms in the question are assumed to be the radioactive isotope and its decay product

the isotope (K-40) is only .0117% of natural K

using total Ar and total K would give an age prior to the "Big Bang"

Answer 3

thanks for the tip, but I am a little lost about total Ar and K. The question just says that there is 5 times more potassium but how do we know the actual number of potassium atoms compared to argon