Fourth-graders Vincent Gallo, left, Raylene Henry, Diane Zavadsky, Brian Foley and Stacy Stewart collect litter for an Earth Day project at Broad Street School in Butler on April 21, 1970. Marguerite Geibel's class was one of the first groups to start participating in the now-annual observance, which was started by U.S. Sen. Gaylord Nelson, D-Wis., that year. Earth Day is now held every April 22 by more than 500 million people in 175 countries.