Sheryl Leighton vividly remembers the first Earth Day on April 22, 1970, because she didn’t have to wear a skirt to school.

She was just 16 and her public high school in Washington state normally required girls to wear dresses or skirts, but made an ecological exception for the female students who were picking up trash at a local lake that day.

“We got to wear pants,” she said, adding she can still recall the smell of the stale beer in the bottles they gathered that day.

On Sunday, Leighton, 65, celebrated her 50th Earth Day — one day early — in Berkeley with dozens of veteran vegans, conservationists, entrepreneurs and eco-conscious consumers in what has become a global environmental event.

Many wore their environmental hearts on their sleeves, with one participant proclaiming via his T-shirt that he was a “ferocious vegan” while another was a “plant-based princess.”

People milled around tables dedicated to environmental causes like clean air or booths focused on eco-consumerism. One table offered organic kombucha and another environmentally conscious cutlery — stainless steel forks, spoons, straws and chopsticks in a washable pouch.

Berkeley Earth Day organizer Hope Bohanec said the event was focused on celebration and inspiration — a festival of the kinds of choices that can make an environmental difference.

“That’s what Earth Day is,” she said, “so we don’t feel so hopeless.”

The first Earth Day is generally considered the birth date of the modern environmental movement as activists countered air and water pollution, especially after a large oil spill off the coast of Santa Barbara in 1969.

“Groups that had been fighting against oil spills, polluting factories and power plants, raw sewage, toxic dumps, pesticides, freeways, the loss of wilderness, and the extinction of wildlife suddenly realized they shared common values,” according to the Earth Day Network.

This year, an estimated 3,000 cleanup activities are scheduled in communities across the United States, in addition to other events.

“Every organization from the Smithsonian to the government of Quebec and local organizations in Rome are holding meaningful events that encompass the Earth Day spirit — global reach, local action,” Kathleen Roger, president of the organization, said in a statement.

While Earth Day remains focused on picking up trash and keeping the air and oceans clean, it’s changed over the years, Bohanec said.

“I’ve seen it going way more corporate,” she said, noting that she’s seen events sponsored by oil or chemical companies. Berkeley’s event remains free of corporate sponsors, she said.

There was also little to no environmental nail-biting over climate change or oceans choked with plastic.

Instead, participants surveyed organic chocolate and organic, soy-free, vegan, gluten-free, non-GMO juice and learned about “veganic farming” and the Berkeley City Council’s adoption of Green Monday, which encourages residents to eat only plant-based food one day a week.

Leighton, a volunteer at the event, said that since her first Earth Day five decades ago, she has focused on living an environmentally conscious life — going car free, carrying reusable food containers, carrying a water bottle, using no plastic and living in a small studio.

She doesn’t dwell on rising sea levels or near-extinct animals, focusing instead on her own daily pro-Earth efforts.

“How does it really benefit us to sit and feel sad?” she said. “The solution is somewhere else.”

Jill Tucker is a San Francisco Chronicle staff writer. Email: jtucker@sfchronicle.com Twitter: @jilltucker