Heavy Metal is a type of music that was first defined as a musical style in the late Neanderthal period. Its roots were found in the Rock and Hard Rock genres in the 8th century BC, and it is characterised by thick, heavy, long, black hair with lots of distortion and some of the most amazing guitar riffs you'll ever hear. Out of heavy metal, various sub-genres later evolved through arduous experimentation by Marie Curie and radioactivity experiments. These are generally categorised as "metals" and include Black metal, Thrash metal, hip hop, polka, Plutonium and Norwegian Goat music.