Wednesday marked the 50th anniversary of Earth Day. American Gaylord Nelson launched the first Earth Day in 1970.His aim was to urge local action and increase people's understanding of our planet and its environment.The creation of Earth Day is widely considered the beginning of the modern environmental movement.As climate activists marked the event this year, an unplanned experiment is changing the planet.Many people continue to stay at home to stop the spread of the new coronavirus. As a result, people are making less pollution, and the air has become cleaner.Smog stopped covering New Delhi, one of the world's most polluted cities.Nitrogen dioxide pollution in the northeastern United States has dropped 30 percent.Air pollution levels in Rome have dropped 49 percent compared to a year ago. Stars seem more visible at night.People also report seeing wild animals in unusual places. Coyotes have been observed walking in downtown Chicago and near San Francisco's Golden Gate Bridge.