Radon originates from Uranium 238.  Almost anywhere in the world you can find some radioactive Uranium 238 in the soil.  Radioactive simply means that the element or atom occasionally loses part of itself and changes into a different element.  The energy released as the atom changes is known as radioactive decay and causes varying amounts of damage to whatever surrounds it.  Uranium 238 goes through a number of decays  before becoming radon.  All the elements before and after radon are solids. 

Radon, however, is a noble gas which means it can freely move through the soil.  Radon also has just enough life span (half of it decays in 4 days) to float through the soil and then into our homes.

Radon is a cancer-causing radioactive gas that you can’t taste, see or smell. The U.S. Environmental Protection Agency and Surgeon General’s Office estimated that 20,000 lung cancer deaths are caused each year by radon with radon being the second leading cause of lung cancer and costing upwards of $2 billion a year in direct and indirect healthcare costs.