Answer the following question given this paragraph: 

A low level of radiation occurs naturally in the environment. This is called background radiation. One source of background radiation is rocks, which may contain small amounts of radioactive elements such as uranium. Another source is cosmic rays. These are charged particles that arrive on Earth from outer space. Background radiation is generally considered to be safe for living things. You can learn more about background radiation with the animation at this URL: http://www. pbs. org/wgbh/nova/dirtybomb/sources. html.


Q: A low level of radiation occurs naturally in the environment and is called what?


A:
background radiation