On April 22, 1970, the first Earth Day, millions of Americans around the country went outside for teach-ins and community cleanup events, in addition to marches protesting the mistreatment of the planet.
Compared to protests about racial inequality or the Vietnam War, the environment at the time was seen as a neutral cause that everyone could get behind — so much so that the original Earth Day was proposed by a US senator (Gaylord Nelson, from Wisconsin of all places) who worked with ecology professor Morton Hilbert and activist Denis Hayes to put it all together.
There hadn't been a concerted public effort to undermine science yet, so the main counterargument to Earth Day at the time was that because it fell on the 100th anniversary of Lenin's birthday, the movement was somehow communist. In actuality, the date had been chosen at random because it suited college break schedules.
There wasn't another Earth Day celebration until 1990, and it didn't become an annual event until 2000. While climate change was not yet a major topic at the original Earth Day, some of the demands for sustainable energy and more careful consumption are in line with the student-led climate marches of 2019, which drew millions of schoolchildren to the streets.