A little out of my field of research, but a definite interesting area of hobby-science for me (I have a mild obsession with all things floating in the Universe!).
So, the Earth’s atmosphere first. When the Earth formed from all the matter floating about after the Big Bang, the atmosphere consisted of gases that were released from volcanoes. After that, early living creatures (like bacteria) started to grow in number as they changed to better suit their surroundings. By creating lots of different gases, like oxygen, the gases in the atmosphere changed over time. I’ve literally as of this morning been reading about the Great Oxidation Event, which is an event that altered our atmosphere in such a dramatic way that it changed the nature of creatures that could live on Earth in a huge way. We may not be here had it not been because of this event, however I had never heard of it before! That comes under geology, but it’s worth having a read about it. It’s basically when the Earth’s atmospheric oxygen level rocketed, forcing life to adapt to the oxygen being around. There have always been fluctuations in the levels of gases in the atmosphere, but it’s basically there as a blanket layer of gases that are being emitted from life and geology on Earth. It is also really handy, as it helps protect the Earth from the Solar Wind, which is a constant stream of charged particles that flows from the Sun towards Earth. They’re not great, although they do contribute to the amazing Northern Lights (which is on my list of things to see!).
Now to the moon! Please forgive me, but we’re walking through this learning journey together on this one. You, me, and the power of Wikipedia. If anyone ever tells you that you’re not allowed to use Wikipedia as a point of factual reference, don’t believe them. Just double check the actual references that Wikipedia has used, as it’s a great place to start, and working with the references that they have there is better than nothing! The moon seems to have a very thin atmosphere – a lunar atmosphere – but it is practically a vacuum (meaning empty space – imagine air, only with all of the air sucked out of it. Like in the episode of Doctor Who recently with House, that consumed the Tardis, and was playing tricks on them, like sucking the air out of the main control room). This is why the astronauts that did the moon landings had to have oxygen being fed through their masks. Our particular moon doesn’t seem to have anything on or within it to produce any gases that could form an atmosphere, however I know that moons of other planets have atmospheres. Titan, a moon of Saturn, has a really dense atmosphere. It’s not my favourite moon though – Phoebe, another of Saturn’s moons, is my favourite, as she rotates the wrong way, she’s really wonky, and is just totally mad! No idea whether she has an atmosphere though… I’ll have to ask my friend Space Boy, who is an astronomer…
Did that answer your question? If not, let me know!