(October 3, 2013 at 4:04 pm)John V Wrote:(October 3, 2013 at 3:48 pm)Esquilax Wrote: So when one uses K-Ar dating on lunar rocks, it shows that they are younger because what is being shown is the date of the last heat and impact event, not the age of the actual rocks, which would fit in with the other brackets, presumably. I don't get what you're missing, here.Again, heating events "early" in the moon's history would give ages not much more recent than other methods. you know that - that's why you didn't quote it yourself, but claimed "regular meteor hits" without support.
What?
If I have a rock that has K40 in it, and it cools forming a feldspar (KAl3Si3O8), it will then begin to spontaneously decay its K40 to Ar40.
If that rock remains undisturbed, then I could measure the ratio of K40 to Ar40 and use the rate of decay to get an age.
If however that rock is heated up and the crystal lattice expands due to a change in density, the Ar40 generated from the decay will escape as it does not fit into the structure of the feldspar crystal lattice. Resetting the age to 0. Then you close that system again and it starts over.
Meaning that you measure the heating event and not the original age.
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