Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potassium is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites. In these materials, the decay product 40Ar is able to escape the liquid (molten) rock, but starts to accumulate when the rock solidifies (recrystallizes).

Crazy.

I left out the cold mountain tops. This seems like an easy one. Hot air rises because it is less dense than the surrounding air, and the density is related to the ambient pressure. As the hot air rises, the pressure decreases, so the temperature of the rising air will decrease according to Boyle's or Charles' law.

That explains why a column of hot air would cool off as it rises, but not why the atmosphere is typically colder at elevation. I suppose what heat there is in the atmosphere comes from the sun warming the Earth's surface, heating the air by conduction, so temperatures drop as you get farther from the surface. If that's true, then we would expect high-elevation places like Denver to have similar temperatures to low-altitude places at a similar latitude, but higher places appear to have lower temperatures even when they are not mountain tops.

Maybe this one is not so easy. Ideas?