This recent post by the National Academies provides another good overview of Earth Day and the science around it.
Here is an excerpt.
THE NATIONAL ACADEMIES
ADVISORS TO THE NATION ON SCIENCE, ENGINEERING, AND MEDICINE
By Lisa Pickoff-White
April 21 – April 22 marks the 36th anniversary of Earth Day, a day of celebration and activism intended to raise awareness of environmental issues. In 1970 the Environmental Teach-In, led by U.S. Senator Gaylord Nelson and Denis Hayes, helped organize around 20 million demonstrators to show support for a policy agenda focused on these concerns.
Many laws to protect the environment, including the Clean Air Act, were passed by Congress in the wake of the 1970 Earth Day. And the U.S. Environmental Protection Agency was created to protect the environment and public health.
Several National Academies reports from the past year examine how science and technology can be harnessed to protect the Earth and sustain the diversity and well-being of the life it supports.