2010 marked the 40th celebration of Earth Day, a holiday that helped spark America's modern environmental movement when it was founded on April 22, 1970, by then-Sen. Gaylord Nelson of Wisconsin. In honor of that historic day, MNN produced this quick look back at the last four decades of planetary appreciation.
1971: Amtrak is founded, even though gas costs just 33 cents a gallon.
1972: The EPA bans DDT, which was thinning bald eagles' eggshells.
1973: A Mideast oil embargo sparks a U.S. gas crisis.
1974: Congress passes the Safe Drinking Water Act, shamelessly pandering to the water-drinkers lobby.
1975: Congress sets emissions and efficiency rules for cars, leading to the introduction of catalytic converters.
1977: The U.S. adds the first plants to its endangered species list — despite their disturbing lack of cuteness.
1978: Congress bans CFCs in aerosol sprays after scientists realize they can deplete the Earth's ozone layer.
1979: A partial meltdown at Pennsylvania's Three Mile Island nuclear plant ruins an otherwise good day.
1980: Congress creates the Superfund program to clean up toxic waste sites. Those expecting "super fun" sites are quickly disappointed.
1981: Acid rain intensifies over the Northeastern United States and Canada.
1982: Dioxin contamination forces the U.S. government to buy homes in Times Beach, Missouri — not the last time it would have to buy up toxic assets.
1983: A long failure to clean up the Chesapeake Bay begins.
1984: 8.6 million acres of protected wilderness are established in 21 states. Somewhere in the distance, a coyote howls.
1985: Scientists discover a giant hole in Earth's ozone layer. During the next year's NBA All-Star Game, Spud Webb dunks through it.
1986: Congress declares the public has a right to know when toxic chemicals are released into the air, land or water. The public breathes a sigh of relief — and a little sulfur dioxide.
1987: Medical waste washes ashore in New York and New Jersey, forcing beaches to close. Efforts to rebrand the area don't work out.
1988: Congress bans ocean dumping of sewage sludge and industrial waste, ending a cherished American tradition.
1989: The Exxon Valdez spills 11 million gallons of crude oil into Alaska's Prince William Sound, one of the worst environmental disasters in U.S. history.
1990: The EPA's Toxic Release Inventory tells the public which pollutants are being released into their communities.
1991: The U.S. government begins using products made from recycled content.
1992: The U.S. Energy Department and the EPA launch the Energy Star program to label energy-efficient products.
1993: A cryptosporidium outbreak in Milwaukee sickens 400,000 people and kills more than 100, raising awareness of microbes in water supplies.
1994: The first genetically modified tomatoes hit the U.S. market.
1995: Wolves are reintroduced into Yellowstone and central Idaho. The initial awkwardness quickly fades.
1996: Public drinking-water suppliers are required to inform customers about chemicals and microbes in their water.
1997: The U.S. joins other countries in Kyoto, Japan, to negotiate a global climate-change treaty it winds up rejecting.
1998: Earth has its warmest year since record keeping began in 1880.
1999: The EPA announces new rules to improve air quality in national parks and wilderness areas. Somewhere in the distance, a coyote coughs.
2000: High temperatures and low rainfall spark the worst U.S. wildfire season in 50 years.
2001: The U.S. formally rejects the Kyoto treaty. The treaty suffers brief self-esteem issues before hooking up with Europe on the rebound.
2002: The U.S. suffers its second-worst wildfire season in 50 years.
2003: The EPA retrofits 40,000 school buses nationwide to cut back their tailpipe emissions.
2004: The EPA requires cleaner fuels and engines for farm and construction equipment.
2005: The 2005 Atlantic hurricane season produces a record number of tropical cyclones, including Hurricane Katrina, which devastates the Gulf Coast.
2006: An Inconvenient Truth is released, winning Al Gore an Oscar, a Nobel Prize and a lifetime of being criticized every time it snows.
2007: The bald eagle is removed from the endangered species list.
2008: The EPA releases a list of "eco-fugitives." Captain Planet comes out of retirement.
2009: Something happens in Copenhagen, but no one is sure what, if anything, it is.
2010: People around the world celebrate the 40th Earth Day, once again dedicating a full day to the planet's health. The Earth is touched, even though it creates days in the first place by rotating, which means "Earth Day" is a regift. But it's the thought that counts.
Sources: EPA, U.S. Energy Department, U.S. Fish and Wildlife Service, National Oceanic and Atmospheric Administration, NASA