Earth Day has its roots in growing concern over pollution in the 1960s, when author Rachel Carson's 1962 book “Silent Spring,” about the pesticide DDT and its damaging effects on the food chain, hit bestseller lists and raised awareness about nature's delicate balance.

For the 55th year, the world is using the day to celebrate Mother Nature and the wonderful planet we live on. "Earth Day really is a symbol of the environmental movement," Sarah Davies, the director of communications and media at EarthDay.