March 21, 1981: Inspired by author Edward Abbey and his book "The Monkey Wrench Gang", activists unfurl a large roll of black plastic down the face of the Glen Canyon Dam, depicting a symbolic crack in the dam. The controversial dam had changed the ecosystem of a large stretch of the Colorado River. The event spawns the group Earth First!
March 21, 1994: The U.N. Framework Convention on Climate Change (UNFCCC) takes effect, the first global agreement on addressing climate change.
March 21, 1995: Gray wolves are released in Yellowstone National Park. The wolves (one seen at right), wiped out in much of the West in the early 1900s, are now the object of a long court battle between conservationists and ranchers, who fear that the wolves will prey on livestock. Within ten years, the wolf restoration project is considered a complete success.
Photo: USFWS Endangered Species/Flickr