Re: Just a non-biologist type question
The biologist-type answer to that is that our universe is pretty much set up to make life happen, eventually, etc.
Young planets are basically huge chemical reactors, and produce a lot of the basic elements of what we currently assume are needed for life. If the right conditions are there: mostly liquid water, pressure and a bit of heat at the right range, all those basic elements follow the dance of chemistry and random chance and both RNA and proteins will form. Some of that will have their own chemical properties, and....
A lot of that sequence depends, etc. But the conditions needed for it aren't that extreme, and still exist around volcanic areas here until this day. And are used by us ( under controlled conditions, but the chemistry is the same..) for those PCR tests we're all bothered by currently.
And cosmic rays don't kickstart anything. They are so energetic they smash things to bits. To the point of shooting right into our planet and going right through it only slowing it down a bit on occasion. Our magnetosphere doesn't do much to protect us from that, really. What it does do is prevent our planet from being stripped bare and terminally irradiated by the solar wind.
Venus has an atmosphere because of its gravity well and the fact that the main atmospheric components are CO2 and sulphuric acid. Heavy stuff. Mars, being much smaller, didn't stand a chance, and while it may have had some microbial life in its historical oceans, those have been stripped while the planet was still relatively warm. Else it would still have plains of ice instead of just desert. Pluto does have plains of ice, but even that far out the solar wind strips away its atmosphere in "summer" when it actually has one. That's how important a geomagnetic field is: It keeps the water in.