A look back

April 22, 1970: The first Earth Day occurs after U.S. Sen. Gaylord Nelson calls for a nationwide environmental protest and 22 million Americans demonstrate against oil spills, polluting factories, toxic dumps, pesticides, freeways and wildlife extinction.

December 2, 1970: Under the Nixon administration, the U.S. Environmental Protection Agency begins operating to protect human health and safeguard the natural environment.

December 7, 1972: The crew of the Apollo 17 spacecraft takes the “Blue Marble” photograph, and for the first time Earth appears as a fragile and vulnerable entity.

December 28, 1973: President Richard Nixon signs the Endangered Species Act, which becomes one of the most powerful legislative tools for protecting the environment.

Mid-1970s: Urban dwellers leave cities in favor of rural areas as part of the “back-to-the-land” movement. The mass migration stems from discontent over rampant consumerism, the Watergate scandal, the Vietnam War and the energy crisis.

March 28, 1979: Three Mile Island nuclear power plant has a partial core meltdown, and public reaction against nuclear power grows in the aftermath of the accident.

October 14, 1979: Greenpeace becomes an international organization, with a branch in the United States. The organization protests whaling, the destruction of old-growth forests, nuclear power and, later, genetic engineering.

April 22, 1990: Earth Day reaches global heights. More than 200 million people in 141 countries participate in protests and celebrations.

December 10, 1997: Julia “Butterfly” Hill climbs into a California coast redwood tree to prevent its destruction, climbing down two years later after securing the tree’s life.

October, 1998: Earth Liberation Front forms in the United States, calling for economic sabotage and guerrilla warfare to stop the exploitation of the natural environment. ELF becomes front-page news for claiming responsibility for burning down a ski resort in Colorado.

August, 2006: Al Gore’s An Inconvenient Truth hits theaters, drawing widespread attention to the climate crisis. The documentary later earns an Academy Award.

December 11, 2007: Kyoto Protocol commemorates its 10th anniversary. The United States still refuses to ratify the international treaty.