Forty-seven years ago, on April 22, 1970, twenty million Americans took to the streets to voice their concern about the deteriorating environment and urge the government to take action before was too late. The grassroots movement, which is now celebrated by over 2 billion people in 192 countries, led to the enactment of numerous environmental laws, including the Clean Air Act of 1970 and the Endangered Species Act of 1973.