Earth Day

Sources

• U.S. Senate Historical Office, Gaylord Nelson Promotes the First Earth Day — https://www.senate.gov/artandhistory/history/minute/Gaylord_Nelson_Promotes_the_First_Earth_Day.htm → Nelson as a United States senator (D-WI); his September 1969 request that his staff work out how to sponsor nationwide campus environmental teach-ins the following spring; the choice of the week of April 19–25 and then of Wednesday, April 22; the turnout of about 20 million Americans at roughly 2,000 college campuses, 10,000 primary and secondary schools and hundreds of communities.
• Congressional Research Service, Earth Day: Fact Sheet, report R46293, updated April 9, 2026 — https://www.everycrsreport.com/files/2026-04-09_R46293_daaf5d177adca01d5e7471d5a1cc8ffd08a78a70.html → that Nelson told an audience in Seattle on September 20, 1969; the choice of a weekday after the end of winter weather but before final exams, to maximize students' participation; that CRS itself says only that millions of Americans participated, citing Gladwin Hill in the New York Times of April 23, 1970; and the resolutions in the 92nd, 93rd and 106th Congresses to designate an annual Earth Day, on which no further action was taken. (This is the everycrsreport mirror; the citation of record is CRS R46293 at crsreports.congress.gov, which refused automated retrieval.)
• Federal Highway Administration, U.S. Department of Transportation, highway history and NEPA — https://www.fhwa.dot.gov/highwayhistory/nepa/04.cfm → the September 1969 Seattle conference and the announcement there; Wednesday, April 22, 1970; Congress in recess because so many members were at Earth Day events; rallies of as many as 25,000 each in Chicago, New York and Philadelphia; 10,000 at a Washington Monument rally.
• Encyclopaedia Britannica, Earth Day — https://www.britannica.com/topic/Earth-Day → the first Earth Day as an environmental teach-in; about 20 million participants; Denis Hayes as a Harvard graduate student hired by Nelson; Fifth Avenue closed to traffic in New York; roughly 10,000 at the Washington Monument; the 1990 global Earth Day organized by Hayes; and the Paris Agreement opened for signature on Earth Day 2016.
• Wisconsin Historical Society, A Commemoration of Conservation: The Story of Earth Day — https://wisconsinhistory.org/Records/Article/CS16311 → Nelson's recruitment of the Republican congressman Paul "Pete" McCloskey as co-chair so the event had no partisan lean; that it was organized in six months; state archivist Matt Blessing's estimate of 10 to 20 million participants and more than 2,000 colleges and universities; and that April 22, 1970 was a Wednesday.
• NOAA IncidentNews, Santa Barbara well blowout — https://incidentnews.noaa.gov/incident/6206 → the January 28, 1969 blowout at Union Oil Company well number 21 under Platform A, 5.5 miles southeast of Santa Barbara, and the 100,000 barrels released until December 1969.
• EARTHDAY.ORG, Earth Day History — https://www.earthday.org/history/ → that Nelson proposed Earth Day after the January 1969 Santa Barbara spill; the weekday chosen between spring break and final exams; about 20 million Americans in 1970; the 1990 global event; and the organization's claim that the first Earth Day led to the creation of the EPA.
• EPA, The Origins of EPA — https://www.epa.gov/history/origins-epa → President Nixon's Reorganization Plan No. 3 message to Congress on July 9, 1970, and the Senate's confirmation of the first administrator on December 2, 1970 as the date EPA uses as the birth of the agency.
• EPA archive, EPA History: The Clean Air Act of 1970, essay by Representative Paul G. Rogers — https://www.epa.gov/archive/epa/aboutepa/epa-history-clean-air-act-1970.html → that the juxtaposition of Earth Day and the 1970 amendments was no accident, and that the public pressures created by the Earth Day movement provided the necessary impetus.
• U.S. Fish and Wildlife Service — https://www.fws.gov/story/2013-12/endangered-species-act-turns-40-december-28 → the Endangered Species Act signed into law on December 28, 1973, with no Earth Day attribution made.
• EPA, History of the Clean Water Act — https://www.epa.gov/laws-regulations/history-clean-water-act → the sweeping 1972 amendments, with no Earth Day attribution made.
• UNFCCC, 175 States Sign Paris Agreement — https://unfccc.int/news/175-states-sign-paris-agreement → the signature ceremony at United Nations headquarters in New York on April 22, and that 175 Parties — 174 countries and the European Union — signed, with 15 states depositing instruments of ratification.
• University at Buffalo, Adam Rome on the 50th anniversary of Earth Day — https://www.buffalo.edu/news/tipsheets/2020/009.html → "It wasn't one event. It was at least 12,000."
• EARTHDAY.ORG, Register Your Cleanup with The Great Global Cleanup — https://www.earthday.org/actions/register-a-cleanup/ → year-round registration, the guides for individuals and groups, and the global event map.
• EPA, Examples of Participatory Science Projects Supported by EPA — https://www.epa.gov/participatory-science/examples-participatory-science-projects-supported-epa → the Cyanobacteria Monitoring Collaborative and its bloomWatch app, and the Chesapeake Monitoring Cooperative's volunteer water quality monitoring.
• National Park Service, volunteer programs — https://www.nps.gov/subjects/volunteer/programs.htm → the Park Service's citizen science programs (https://www.nps.gov/subjects/citizenscience/index.htm) and the National Parks BioBlitz (https://www.nps.gov/subjects/biodiversity/national-parks-bioblitz.htm).
• Wisconsin Historical Society, An Earth Day Gallery in Gaylord Nelson's Honor — https://www.wisconsinhistory.org/Records/Article/CS3745 → the Gaylord Nelson papers at 1,040 boxes of paper, audio recordings, films, photographs, scrapbooks and video recordings, available to the public during regular archives hours with an online finding aid; and the gallery of 130 photographs covering 1954 to 2006.

Source conflict, resolved and disclosed: the 1970 participation figure. Five sources give about 20 million, the Wisconsin Historical Society's own archivist gives a range of 10 to 20 million, and the Congressional Research Service declines a figure and falls back on the contemporaneous New York Times, which said only "millions." This page reports the spread and names who says what rather than averaging, because no source traces 20 million to a count. On causation the page follows the more primary source in each case: EPA's archive where EPA itself claims Earth Day as an impetus (the 1970 Clean Air Act amendments), and the documenting agency where it makes no such claim (the Clean Water Act and the Endangered Species Act), rather than EARTHDAY.ORG's broader account.

Not claimed, for want of a source: that April 22 was chosen because it is Vladimir Lenin's birthday — no reputable source supports it, and the one acceptable source that touches the question renders the dates in a way that appears to be mistaken, so this page does not rely on it and gives only the documented academic-calendar reason; the enactment dates of the 1970 Clean Air Act amendments and the 1972 Clean Water Act, which EPA's own history pages do not state; any methodology or primary count behind the 20 million figure; Denis Hayes's exact age on the day itself (Harvard dates him at 25 in 1969); Pete McCloskey's district or the formal title of his role; the country counts for 1990 (EARTHDAY.ORG says 141, Britannica says more than 140) and the participation figures for 2000, 2010 and the present day, which are self-reported by the organizing body and uncorroborated; the sales figures usually given for Rachel Carson's Silent Spring; and any government assessment linking the Santa Barbara spill to the environmental movement or to legislation — NOAA confines itself to the incident and describes its environmental effects as relatively minimal.

Rejected as sources: nationaltoday, nationaldaycalendar, checkiday, timeanddate, history.com, and content-farm or AI-generated listicles. Advocacy and opinion outlets were also set aside on the Lenin question, which is why that claim is left unaddressed beyond the note above.