Final answer:
The issues that motivated organizers to plan a national "teach-in" on the environment in 1969 were concerns about pollution, toxic waste, and the preservation of natural resources. Earth Day was first observed on April 22, 1970, and has since become a global event.
Step-by-step explanation:
The issues that motivated organizers to plan a national "teach-in" on the environment in 1969 were concerns about pollution, toxic waste, and the preservation of natural resources. These concerns were fueled by a series of environmental disasters and the increasing political awareness of the public.
One of the major victories for the environmental movement was the passage of the Clean Air Act of 1963, which regulated auto and factory emissions. Wisconsin senator Gaylord Nelson proposed the idea of a teach-in on environmental issues to colleges and universities, and on April 22, 1970, the first Earth Day was observed.
Since its inception, Earth Day has been celebrated every year on April 22 and has become a global event, raising awareness about environmental issues and mobilizing millions of people around the world.