It takes millions of years for uranium to decompose into radium. It is the radium that gives off radon gas. The final stage of uranium's decay is lead. Imagine, one element becoming another. Maybe those alchemists centuries ago weren't so far off attempting to change lead into gold.
Radon enters a building through cracks, dirt floors, drains, and porous concrete foundations.
It is drawn into the home as air is sucked in by the furnace for combustion. As air exits the chimney it creates a partial vacuum. This is especially true during winter months when the ground is frozen and furnaces are blaring. The resulting pressure difference draws air and radon from beneath the home through any available openings. Concentrations of radon will vary depending on the building's construction style and the amount of radon present in the soil underneath it.