After its inaugural celebration in 1970, Earth Day continued as a day of environmental action and education. It wasn't until its 20th anniversary in 1990, though, that it would begin to transform into the truly international endeavor we know today.

Organized in different ways by two groups led by Earth Day 1970 organizers - Dennis Hayes' Earth Day 1990 and Edward Furia's Earth Day 20; Gaylord Nelson was the honorary chair for both - the 1990 events brought bigger budgets and stronger marketing. Successful crowdsourcing, television and radio presence - even a song recorded by a host of country music all-stars - strongly pushed for materials recycling. People from 141 nations participated - an estimated 200 million of them.

As Earth Day pushed through the millennium and beyond many places have shifted to an entire Earth Week instead of just a single day, in an effort to show that more than a single day should be devoted to environmental causes. As any environmental scientist would say - taking action once a year is good, but it is not enough.

Large-scale rallies, parades, and major cleanup efforts have become commonplace as Earth Day has grown into the largest secular observance in the world, with at least a billion people participating. Celebrity appearances - a group as diverse as John Ratzenberger, Leonardo DiCaprio, and Chuck Berry, to name but three - are regular occurrences at events, lending their ability to reach people to the cause. A great deal of promotion and coordination is done by the Earth Day Network (a continuation of Hayes' Earth Day 1990), assisting groups around the globe in their efforts on both national and community levels.