re: Questions
"Why does water boil easier in a lower pressure?"
Far as I'm aware, water doesn't boil easier in lower pressure- it boils at lower temperature, but not more easily.
Lower temperature means less energy input, less energy input means that the molecules of water change from liquid to vapor state with less energy. In other words the change from one form to another poses less difficulty to the input energy, hence "easier."
But in any case, lowering the surrounding pressure lowers the boiling point, the question is: Why does such effect take place?
"Why does evaporating water cause a cooling effect?"
Well anything that evaporates causes cooling- but has water has high latent energy- and that is probably due how water is structurely formed at molecular level.
Would it be proper to say that: The kinetic energy that the molecules have gained in order to separate from the surface of the liquid is removed from the liquid by the departing molecules, in the process the liquid has lost the kinetic energy of the molecules and also the energy that caused the molecules to escape from the liquid.
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"Why does radioactive material heat its surroundings?"
Because it's emitting radiation.
You are right, but the question I should have posed was: What is the mechanism that causes molecules in the vicinity of radioactivity or radiation to gain in kinetic energy?
"Is there more radioactive material in the atmosphere now than there was before our "nuclear age"?"
Coal plants emit a lot of radioactive material- not sure whether nuclear bombs have put more radioactive material in atmosphere than compared to coal plants. Not sure if all radioactive that human activity has added to atmosphere is significant. I would agree that an alien civilization could detect the type of radioactive material in Earth and surmise that an advanced civilization was on Earth. But on the simple level of just more radioactive material vs less radioactive material- that would be less clear.
I read somewhere that the background radiation had increased in the years after the nuclear bomb explosions in the atmosphere, I do not know if it has decreased after the treaties that stopped that kind of testing in the atmosphere.
There is a good area for more scientific study to see what is happening in (and to) the atmosphere regarding radioactivity and radiation.
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You have some really good questions there, it will take a smarter man than I to answer them.