Let's stay on point. Global cooling did not "hatch" earth day. The two things in 1969-70 were unrelated. The initial earth day was about a lot of environmental things. Global cooling wasn't one of them.
This is a brief piece on the beginning of earth day.
http://www.earthday.org/about/the-history-of-earth-day/
If your teacher decided to connect global cooling and earth day, he/she did that on her own. I was a bit older than you in 1970, and I'm certain global cooling never came up when we were planning earth day at my school. And I'll stick by my recollection that the global cooling debacle mainly took hold after the Newsweek article in 1975, despite random references prior to that date, which is still irrelevant to the start of earth day.
My reaction is primarily based on the fact that an article that has been disavowed by the scientists on which it was based because the analysis was wrong, and which even the author said it is memorable only for being fodder for the right to make fun of science, still comes up regularly, usually out of context.
