Hard hats, worn by construction workers, were first used in the building of the Hoover Dam in 1933. Hydrogen is the most common atom in the universe. If all of the gold sitting in the oceans and seas were mined, every person in the world would get about 44 pounds of gold each. In Australia, a dust devil is called a “”willy-willy.”” Central air conditioners use 98 percent more energy than ceiling fans.