EarthDaywasfirstobservedinSpringof1970.Anestimated20millionpeoplenationwideattendedfestivitiesoutofwhichcamethelargestgrassrootsenvironmentalmovementinU.S.history,andtheimpetusfornationallegislationliketheCleanAirandCleanWaterActs.Bythetwentiethanniversaryofthatevent,April22,1990,morethan200millionpeoplein141countriesparticipatedinEarthDaycelebrations.
FormerU.S.SenatorGaylordNelson,EarthDay’sco-founder,modeledEarthDayonanti-VietnamWardemonstrations,called"teach-ins,"thatwerecommononcollegecampuses."AtaconferenceinSeattleinSeptember1969,Iannouncedthatinthespringof1970therewouldbeanationwidegrassrootsdemonstrationonbehalfoftheenvironment,"saysNelson."Theresponsewaselectric.Telegrams,letters,andtelephoneinquiriespouredinfromallacrossthecountry."Asmanyas20millionAmericansparticipatedinenvironmentalrallies,demonstrationsandotheractivitiesinthe1970EarthDay.
SincethefirstEarthDay,however,theenvironmentalmovementhasincreasinglytransformeditselffromalargelygrassroots,citizencrusadetoaprofessionally-organized,establishedspecialinterest.