Recently had to deal with radon in a basement, leading me to a fun side trek of learning about uranium decay (it has been a lot of years since chemistry classes).

When you hear about alpha decay of radioactive materials, that is the matter spitting off a highly ionized helium nucleus, freshly birthed into this world. That He nucleus rapidly steals electrons from matter, which is how it can be dangerous to human cells if ingested.

All of that helium underground is the result of alpha decay, and a single uranium-238 element will birth 8 helium atoms as it transitions through a series of metals and one gas (radon), then finally finding stability as Pb206. U235 will birth 7, becoming Pb207.

Anyways, found that fascinating. It's just happenstance that helium often gets blocked exiting the crust by the same sort of structures that block natural gas from escaping, and they are an odd-couple sharing little in common.

One other fun fact -- radon only has a half life of 3.8 days. Uranium becomes thorium becomes radium, then radon where it has an average 3.8 days to seep out of the Earth and into our basements, where it then becomes radioactive metals that attach to dust, get breathed in (or eaten) and present dangers. In the scale of things, crazy. Chemistry is fascinating.