Students from the Convent of the Sacred Heart School in New York City sweep up the city's Union Square as part of the first Earth Day on April 22, 1970.

At the time, Pablo Solomon was teaching earth science at a high school in Houston, Texas, where he participated in local Earth Day events.

"I can actually remember many people of my parents' generation remarking that [sweeping up] was the only act of Earth Day that resulted in anything," Solomon said via email. "People of that generation would comment, If those hippies got a haircut and clean clothes, the world would be better."

David Jones, who now lives in Johnson City, Tennessee, was a fourth grade student in North Syracuse, New York.

"We had a young, 'hip' teacher. She told us all to bring in grocery bags to school for something called Earth Day," Jones recalled in an email interview. "That day we all went out on the school grounds and picked up trash, etc.

"There wasnt that much to pick up. There were more kids than trash, really. But it brought the care of the environment into my consciousness and left a lifelong impression on me about the power of people coming together and working together on a cause."