1970-1979 By clairefoltz Apr 22, 1970 The first Earth Day celebration is held Mar 10, 1971 The Senate approves the 26th Amendment, that would lower the voting age from 21 to 18 Oct 1, 1971 Walt Disney World opens in Orlando, Florida Jun 17, 1972 The Watergate crisis begins Jan 30, 1973 Two defendants in the Watergate break-in trial are convicted Aug 9, 1974 President Richard M. Nixon resigns as president Apr 29, 1975 Communist forces complete their takeover of South Vietnam Nov 2, 1976 Carter wins presidential election against Ford Sep 21, 1977 The U.S. signs a nuclear proliferation pact Apr 18, 1978 The United States Senate votes to return the Panama Canal back to Panama on December 31, 1999 Mar 28, 1979 An accident at the Three Mile Island nuclear power plant in Middletown, Pennsylvania occurs when a partial core meltdown is recorded