Timeline: 1970s

April 22, 1970: More than 20 million people participate in first Earth Day.

May 1970: National Guard kills four Kent State students at a protest; police fire on Jackson State protesters, killing two. A nationwide student strike follows, with more than 4 million students closing 900 colleges and universities.

War tax resistance soars to more than 200,000 who refuse to pay the excise taxes on phone bills or income tax.

Military draft ends in 1973. U.S. moves to all-volunteer force. Draft evaders eventually get full pardons.

1974. Richard Nixon resigns from office after the Watergate Scandal.

1976. Toxic Substances Control Act passes, empowering the EPA to track the tens of thousands of industrial chemicals used in the United States, as well as to ban those that pose a threat to the environment or human health.

10-year moratorium ends with the execution of Gary Gilmore by firing squad in Utah, Jan. 17, 1977.

Oklahoma becomes the first state to adopt lethal injection as a means of execution.

Sept. 17, 1978: Camp David Accord sets framework for peace between Egypt and Israel.