The Earth Day flag by John McConnell contains The Blue Marble on a field of blue

Earth Day is an annual day on which events are held worldwide to increase awareness and appreciation of the Earth's natural environment. Now Earth Day is coordinated globally by the Earth Day Network,^[1] and is celebrated in more than 175 countries every year.^[2] In 2009, the United Nations designated April 22 International Mother Earth Day.^[3] Earth Day is planned for April 22 in all years at least through 2015.^[4]

The name and concept of Earth Day was allegedly pioneered by John McConnell in 1969 at a UNESCO Conference in San Francisco. He proposed March 21, 1970, the first day of spring in the northern hemisphere. This day of nature's equipoise was later sanctioned in a Proclamation signed by Secretary General U Thant at the United Nations. About the same time a separate Earth Day was founded by United States Senator Gaylord Nelson as an environmental teach-in first held on April 22, 1970. While this April 22 Earth Day was focused on the United States, an organization launched by Denis Hayes, who was the original national coordinator in 1970, took it international in 1990 and organized events in 141 nations.^[5][6] Numerous communities celebrate Earth Week, an entire week of activities focused on environmental issues.

Wednesday, April 22, 1970 chosen as Earth Day[link]

Gaylord Nelson

The genesis of Earth Day is credited to Gaylord Nelson, a U.S. Senator from Wisconsin. After witnessing the ravages of the 1969 massive oil spill in Santa Barbara, California, and inspired by the student anti-war movement, he called for an environmental teach-in, or Earth Day, to be held on Wednesday, April 22, 1970. Over 20 million people participated that year, and now Earth Day is observed on April 22 each year by more than 500 million people and several national governments in 175 countries.^{[citation needed]} Numerous communities celebrate Earth Week, an entire week of activities focused on environmental issues.

Nelson, an environmental and conservationist activist, took a leading role in organizing the celebration, hoping to demonstrate popular political support for an environmental agenda. He modeled it on the highly effective Vietnam War teach-ins of the time.^[7] Earth Day was first proposed in a prospectus to JFK written by Fred Dutton.^[8] However, Nelson decided against much of Dutton's top-down approach, favoring a decentralized, grassroots effort in which each community shaped its action around local concerns.

Nelson had conceived the idea for his environmental teach-in following a trip he took to Santa Barbara right after the horrific oil spill off the coast in 1969.^{[citation needed]} Outraged by the devastation and Washington political inertia, Nelson proposed a national teach-in on the environment to be observed by every university campus in the U.S.^[9]

I am convinced that all we need to do to bring an overwhelming insistence of the new generation that we stem the tide of environmental disaster is to present the facts clearly and dramatically. To marshal such an effort, I am proposing a national teach-in on the crisis of the environment to be held next spring on every university campus across the Nation. The crisis is so imminent, in my opinion, that every university should set aside 1 day in the school year-the same day across the Nation-for the teach-in.^[9]

One of the organizers of the event said:

"We're going to be focusing an enormous amount of public interest on a whole, wide range of environmental events, hopefully in such a manner that it's going to be drawing the interrelationships between them and, getting people to look at the whole thing as one consistent kind of picture, a picture of a society that's rapidly going in the wrong direction that has to be stopped and turned around.

"It's going to be an enormous affair, I think. We have groups operating now in about 12,000 high schools, 2,000 colleges and universities and a couple of thousand other community groups. It's safe to say I think that the number of people who will be participating in one way or another is going to be ranging in the millions."^[10]

Nelson announced his idea for a nationwide teach-in day on the environment in a speech to a fledgling conservation group in Seattle on September 20, 1969, and then again six days later in Atlantic City to a meeting of the United Auto Workers. Nelson hoped that a grassroots outcry about environmental issues might prove to Washington, D.C. just how distressed Americans were in every constituency. Nelson invited Republican Representative Paul N “Pete” McCloskey to serve as his co-chair and they incorporated a new non-profit organization, Environmental Teach-In, Inc., to stimulate participation across the country. Both continued to give speeches plugging the event.^[11][12][13]

On September 29, 1969, in a long, front-page New York Times article, Gladwin Hill wrote:

"Rising concern about the "environmental crisis" is sweeping the nation's campuses with an intensity that may be on its way to eclipsing student discontent over the war in Vietnam...a national day of observance of environmental problems, analogous to the mass demonstrations on Vietnam, is being planned for next spring, when a nationwide environmental 'teach-in'...coordinated from the office of Senator Gaylord Nelson is planned...."^[14]

Denis Hayes, a Harvard graduate student, read the NYT article and traveled to Washington to get involved.^[15] He had been student body president and a campus activist at Stanford University in McCloskey’s district and where Teach-In board member Paul Ehrlich was a professor. He thought he might be asked to organize Boston. Instead, Nelson eventually asked Hayes to drop out of Harvard, assemble a staff, and direct the effort to organize the United States.^[16][17] Hayes would go on to become a widely recognized environmental advocate.^[18]

Hayes recruited a handful of young college graduates to come to Washington, D.C. and began to plan what would become the first April 22 Earth Day.

Nelson's suggestion was difficult to implement, as the Earth Day movement proved to be autonomous with no central governing body.^[19] As Nelson attests, it simply grew on its own:

Earth Day worked because of the spontaneous response at the grassroots level. We had neither the time nor resources to organize 20 million demonstrators and the thousands of schools and local communities that participated. That was the remarkable thing about Earth Day. It organized itself.^[19]

Official Earth Week logo that was used as the backdrop for the prime time CBS News Special Report with Walter Cronkite about Earth Day 1970 ^[20]

The April 22, 1970, Earth Day marked the beginning of the modern environmental movement. Approximately 20 million Americans participated.^[21] Thousands of colleges and universities organized protests against the deterioration of the environment. Groups that had been fighting against oil spills, polluting factories and power plants, raw sewage, toxic dumps, pesticides, Freeway and expressway revolts, the loss of wilderness, and air pollution suddenly realized they shared common values.

Media coverage of the first April 22 Earth Day included a One-Hour Prime-time CBS News Special Report called "Earth Day: A Question of Survival," with correspondents reporting from a dozen major cities across the country, and narrated by Walter Cronkite (whose backdrop was the Earth Week Committee of Philadelphia's logo).^[20]

Pete Seeger was a keynote speaker and performer at the event held in Washington, D.C. Paul Newman and Ali McGraw attended the event held in Manhattan.^[22]

Earth Day 1970 in New York City[link]

In the winter of 1969-1970, a group of students met at Columbia University to hear Denis Hayes talk about his plans for Earth Day. Among the group were Fred Kent, Pete Grannis, and Kristin and William Hubbard. This New York group agreed to head up the New York City part of the national movement. Fred Kent took the lead in renting an office and recruiting volunteers. "The big break came when Mayor Lindsay agreed to shut down Fifth Avenue for the event. A giant cheer went up in the office on that day," according to Kristin Hubbard (now Kristin Alexandre). 'From that time on we used Mayor Lindsay's offices and even his staff. I was Speaker Coordinator but had tremendous help from Lindsay staffer Judith Crichton."

In addition to shutting down Fifth Avenue, Mayor Lindsay made Central Park available for Earth Day. The crowd was estimated as more than one million—by far the largest in the nation. Since New York was also the home of NBC, CBS, ABC, the New York Times, Time, and Newsweek, it provided the best possible anchor for national coverage from their reporters all over the country.^[23]

Earth Day 1970 in Philadelphia[link]

Edward Furia (left) and Austan Librach (right) in a meeting in early 1970 with the Philadelphia Chamber of Commerce, in which they raised $30,000 to fund Earth Day activities and expose the city's worst polluters ^[24]

U.S. Senator Edmund Muskie speaking to an estimated 40-60,000 at Fairmount Park, Philadelphia on Earth Day, 1970

Earth Day 1970 in Philadelphia gave birth to Earth Week, April 16–22. It was created by a committee of students (mostly from University of Pennsylvania), professionals, leaders of grass roots organizations and businessmen concerned about the environment and inspired by Nelson’s call for a national environmental teach-in. The Earth Week Committee of Philadelphia concluded that devoting only one day to the environment would not provide enough time and space to paint a comprehensive picture of the environmental issues confronting mankind.^[25] While all of their activities would build toward a climactic Earth Day celebration on April 22, there would also be an entire week of events in the week preceding.

Austan Librach, a regional planning graduate student, assumed the role of committee chairman and hired Edward Furia, who had just received his City Planning and Law Degrees from University of Pennsylvania, to be Project Director. The core group from Penn was joined in 1970 by students from other area colleges which, working together, organized scores of educational activities, scientific symposia and major mass media events in the Delaware Valley Region in and around Philadelphia. The Earth Week Committee of 33 members settled on a common objective—to raise public awareness of environmental problems and their potential solutions.^[25][26]

U.S. Senator Edmund Muskie was the keynote speaker on Earth Day in Fairmount Park in Philadelphia.^[25][27] Other notable attendees included consumer protection activist and presidential candidate Ralph Nader; Landscape Architect Ian McHarg; Nobel prize-winning Harvard Biochemist, George Wald; U.S. Senate Minority Leader, Hugh Scott; and poet, Allen Ginsberg. Convicted murderer Ira Einhorn claimed to act as the master of ceremonies,^[28] but this was not the case. The real event organizers dispute this account in a sworn statement saying “Ira Einhorn’s claims that he was a founder or organizer of Earth Day are false. He is a fraud. His lies do a real disservice to those of us who were and are deeply concerned about our planet’s environmental problems and who have worked hard to solve them.”^[29]. In that sworn statement, the organizers indicated that "Einhorn, given a small role on the stage at Earth Day, grabbed the microphone and refused to give up the podium for thirty minutes"^[29] During Einhorn’s murder trial, one of the Earth Day organizing committee members, psychiatrist Donald Nathanson, took the stand and under oath testified that the committee had barred Einhorn from their discussions, considering him a nuisance.^[30]. Again, under oath and penalty of perjury, Dr. Nathanson said there was no master of ceremonies and Einhorn’s only role at the event had been as a liaison with poet and featured speaker Allen Ginsberg. But, Nathanson said, Einhorn didn’t merely introduce Ginsberg — he "commandeered the stage" speaking "incoherently" for half an hour and refusing repeated requests to leave and let the program continue.^[30]

Forty years later, the Earth Week Committee decided to make rare photos, video, and other previously unpublished information about the history of Earth Week 1970 available to the public at EarthWeek1970.org.

Many cities now extend the observance of Earth Day events to an entire week, usually starting on April 16 and ending on Earth Day, April 22.^[31] These events are designed to encourage environmentally aware behaviors, such as recycling, using energy efficiently, and reducing or reusing disposable items.^[32]

Results of Earth Day 1970[link]

Earth Day proved popular in the United States and around the world. The first April 22 Earth Day had participants and celebrants in two thousand colleges and universities, roughly ten thousand primary and secondary schools, and hundreds of communities across the United States. More importantly, it "brought 20 million Americans out into the spring sunshine for peaceful demonstrations in favor of environmental reform."^[33]

Nelson stated that Earth Day "worked" because of the response at the grassroots level. Twenty-million demonstrators and thousands of schools and local communities participated.^[34] He directly credited the first Earth Day with persuading U.S. politicians that environmental legislation had a substantial, lasting constituency.

It now is observed in 175 countries, and coordinated by the nonprofit Earth Day Network, according to whom Earth Day is now "the largest secular holiday in the world, celebrated by more than a half billion people every year."^[35] Environmental groups have sought to make Earth Day into a day of action which changes human behavior and provokes policy changes.^[36]

Earth Day 20 and Earth Day 1990[link]

Mobilizing 200 million people in 141 countries and lifting the status of environmental issues onto the world stage, Earth Day activities in 1990 gave a huge boost to recycling efforts worldwide and helped pave the way for the 1992 United Nations Earth Summit in Rio de Janeiro. Unlike the first Earth Day in 1970, this 20th Anniversary was waged with stronger marketing tools, greater access to television and radio, and multimillion-dollar budgets.^[37]

Two separate groups formed to sponsor Earth Day events in 1990: The Earth Day 20 Foundation, assembled by Edward Furia (Project Director of Earth Week in 1970), and Earth Day 1990, assembled by Denis Hayes (National Coordinator for Earth Day 1970). Senator Gaylord Nelson, the original founder of Earth Day, was honorary chairman for both groups. The two did not combine forces over disagreements about leadership of combined organization and incompatible structures and strategies.^[37] Among the disagreements, key Earth Day 20 Foundation organizers were critical of Earth Day 1990 for including on their board Hewlett Packard, a company that at the time was the second-biggest emitter of chlorofluorocarbons in Silicon Valley and refused to switch to alternative solvents.^[37] In terms of marketing, Earth Day 20 had a grassroots approach to organizing and relied largely on locally based groups like the National Toxics Campaign, a Boston-based coalition of 1,000 local groups concerned with industrial pollution. Earth Day 1990 employed strategies including focus group testing, direct mail fund raising, and email marketing.^[37]

The Earth Day 20 Foundation highlighted its April 22 activities in George, Washington, near the Columbia River with a live satellite phone call with members of the historic Earth Day 20 International Peace Climb who called from their base camp on Mount Everest to pledge their support for world peace and attention to environmental issues.^[38] The Earth Day 20 International Peace Climb was led by Jim Whittaker, the first American to summit Mt. Everest (many years earlier), and marked the first time in history that mountaineers from the United States, Soviet Union, and China had roped together to climb a mountain, let alone Mt. Everest.^[38] The group also collected over two tons of trash (transported down the mountain by support groups along the way) that was left behind on Mount Everest from previous climbing expeditions. The master of ceremonies for the Columbia Gorge event was the TV star, John Ratzenberger, from "Cheers", and the headlining musician was the "Father of Rock and Roll," Chuck Berry.^[38]

Warner Bros. Records released a single in 1990 titled "Tomorrow's World", written by Kix Brooks (who would later become one-half of Brooks & Dunn) and Pam Tillis.^[39] The song featured vocals from Lynn Anderson, Butch Baker, Shane Barmby, Billy Hill, Suzy Bogguss, Kix Brooks, T. Graham Brown, the Burch Sisters, Holly Dunn, Foster & Lloyd, Vince Gill, William Lee Golden, Highway 101, Shelby Lynne, Johnny Rodriguez, Dan Seals, Les Taylor, Pam Tillis, Mac Wiseman, and Kevin Welch. It charted at number 74 on the Hot Country Songs chart dated May 5, 1990.^[40]

Earth Day 2000[link]

Earth Day 2000 combined the ambitious spirit of the first Earth Day with the international grassroots activism of Earth Day 1990. This was the first year that Earth Day used the Internet as its principal organizing tool, and it proved invaluable domestically and internationally. Kelly Evans, a professional political organizer, served as executive director of the 2000 campaign. The event ultimately enlisted more than 5,000 environmental groups outside the United States, reaching hundreds of millions of people in a record 183 countries.^[41] Leonardo DiCaprio was the official host for the event,^[41] and about 400,000 participants stood in the cold rain during the course of the day.

Subsequent Earth Day events[link]

Earth Day 2007 at San Diego City College in San Diego, California

To turn Earth Day into a sustainable annual event rather than one that occurred every 10 years, Nelson and Bruce Anderson, New Hampshire's lead organizer in 1990, formed Earth Day USA. Building on the momentum created by thousands of community organizers around the world, Earth Day USA coordinated the next five Earth Day celebrations through 1995, including the launch of EarthDay.org. Following the 25th Anniversary in 1995, the coordination baton was handed to Earth Day Network.

As the millennium approached, Hayes agreed to spearhead another campaign, this time focusing on global warming and pushing for clean energy. The April 22 Earth Day in 2000 combined the big-picture feistiness of the first Earth Day with the international grassroots activism of Earth Day 1990. For 2000, Earth Day had the Internet to help link activists around the world. By the time April 22 came around, 5,000 environmental groups around the world were on board, reaching out to hundreds of millions of people in a record 184 countries. Events varied: A talking drum chain traveled from village to village in Gabon, Africa, for example, while hundreds of thousands of people gathered on the National Mall in Washington, D.C., USA.

Earth Day 2007 was one of the largest Earth Days to date, with an estimated billion people participating in the activities in thousands of places like Kiev, Ukraine; Caracas, Venezuela; Tuvalu; Manila, Philippines; Togo; Madrid, Spain; London; and New York.^{[citation needed]}

The Earth Day name[link]

According to Nelson, the moniker "Earth Day" was "an obvious and logical name" suggested by "a number of people" in the fall of 1969, including, he writes, both "a friend of mine who had been in the field of public relations" and "a New York advertising executive," Julian Koenig.^[42] Koenig, who had been on Nelson's organizing committee in 1969, has said that the idea came to him by the coincidence of his birthday with the day selected, April 22; "Earth Day" rhyming with "birthday," the connection seemed natural.^[43][44] Other names circulated during preparations—Nelson himself continued to call it the National Environment Teach-In, but press coverage of the event was "practically unanimous" in its use of "Earth Day," so the name stuck.^[42]

Earth Day Network[link]

Denis Hayes

Earth Day Network was founded by Denis Hayes and the organizers of the first Earth Day in 1970 and by other national organizers, including Pam Lippe, to promote environmental activism and year-round progressive action, domestically and internationally. Earth Day Network members include NGOs, quasi-governmental agencies, local governments, activists, and others. Earth Day Network members focus on environmental education; local, national, and global policies; public environmental campaigns; and organizing national and local earth day events to promote activism and environmental protection. The international network reaches over 19,000 organizations in 192 countries, while the domestic program engages 10,000 groups and over 100,000 educators coordinating millions of community development and environmental-protection activities throughout the year.^[45]

In observance of the 40th anniversary of the April 22 Earth Day, Earth Day Network created multiple global initiatives, ranging from a Global Day of Conversation with mayors worldwide, focusing on bringing green investment and building a green economy; Athletes for the Earth Campaign that brings Olympic, professional, and every day athletes' voices to help promote a solution to climate change; a Billion Acts of Green Campaign which will aggregate the millions of environmental service commitments that individuals and organizations around the world make each year;^[46] to Artist for the Earth, a campaign the involves hundreds of arts institutions and artists worldwide to create environmental awareness. EDN mobilized 1.5 billion people in 170 countries to participate in these global events and programs, and helped create Earth Day organizations worldwide.

Earth Day Canada[link]

The first Canadian Earth Day was held on Thursday, September 11, 1980, and was organized by Paul D. Tinari, then a graduate student in Engineering Physics/Solar Engineering at Queen's University. Flora MacDonald, then MP for Kingston and the Islands and Canadian Secretary of State for External Affairs, officially opened Earth Day Week on September 6, 1980 with a ceremonial tree planting and encouraged MPs and MPPs across the country to declare a cross-Canada annual Earth Day. The principal activities taking place on the first Earth Day included educational lectures given by experts in various environmental fields, garbage and litter pick-up by students along city roads and highways as well as tree plantings to replace the trees killed by Dutch Elm Disease.^[47][48]

Paul Tinari officially launching the first Canadian Earth Day on September 11, 1980 - waiting to speak are Flora MacDonald MP, secretary of state for external affairs, Ken Keyes, mayor of Kingston, and Dr. Ronald Watts, principal of Queen's University

Earth Day Canada (EDC), a national environmental charity founded in 1990, provides Canadians with the practical knowledge and tools they need to lessen their impact on the environment. In 2004, it was recognized as the top environmental education organization in North America, for its innovative year-round programs and educational resources, by the Washington-based North American Association for Environmental Education, the world's largest association of environmental educators. In 2008, it was chosen as Canada's "Outstanding Non-profit Organization" by the Canadian Network for Environmental Education and Communication. EDC regularly partners with thousands of organizations in all parts of Canada. EDC hosts a suite of six environmental programs: Ecokids, EcoMentors, EcoAction Teams, Community Environment Fund, Hometown Heroes and the Toyota Earth Day Scholarship Program.

History of the Equinox Earth Day[link]

The equinoctial Earth Day is celebrated on the March equinox (around March 20) to mark the precise moment of astronomical mid-spring in the Northern Hemisphere, and of astronomical mid-autumn in the Southern Hemisphere. An equinox in astronomy is that moment in time (not a whole day) when the center of the Sun can be observed to be directly "above" the Earth's equator, occurring around March 20 and September 23 each year. In most cultures, the equinoxes and solstices are considered to start or separate the seasons.

John McConnell^[49] first introduced the idea of a global holiday called "Earth Day" at the 1969 UNESCO Conference on the Environment. The first Earth Day proclamation was issued by San Francisco Mayor Joseph Alioto on March 21, 1970. Celebrations were held in various cities, such as San Francisco and in Davis, California with a multi-day street party. UN Secretary-General U Thant supported McConnell's global initiative to celebrate this annual event; and on February 26, 1971, he signed a proclamation to that effect, saying:

May there be only peaceful and cheerful Earth Days to come for our beautiful Spaceship Earth as it continues to spin and circle in frigid space with its warm and fragile cargo of animate life.^[50]

United Nations secretary-general Kurt Waldheim observed Earth Day with similar ceremonies on the March equinox in 1972, and the United Nations Earth Day ceremony has continued each year since on the day of the March equinox (the United Nations also works with organizers of the April 22 global event). Margaret Mead added her support for the equinox Earth Day, and in 1978 declared:

"Earth Day is the first holy day which transcends all national borders, yet preserves all geographical integrities, spans mountains and oceans and time belts, and yet brings people all over the world into one resonating accord, is devoted to the preservation of the harmony in nature and yet draws upon the triumphs of technology, the measurement of time, and instantaneous communication through space.
Earth Day draws on astronomical phenomena in a new way – which is also the most ancient way – by using the vernal Equinox, the time when the Sun crosses the equator making the length of night and day equal in all parts of the Earth. To this point in the annual calendar, EARTH DAY attaches no local or divisive set of symbols, no statement of the truth or superiority of one way of life over another. But the selection of the March Equinox makes planetary observance of a shared event possible, and a flag which shows the Earth, as seen from space, appropriate."^[51]

At the moment of the equinox, it is traditional to observe Earth Day by ringing the Japanese Peace Bell, which was donated by Japan to the United Nations.^[52] Over the years, celebrations have occurred in various places worldwide at the same time as the UN celebration. On March 20, 2008, in addition to the ceremony at the United Nations, ceremonies were held in New Zealand, and bells were sounded in California, Vienna, Paris, Lithuania, Tokyo, and many other locations. The equinox Earth Day at the UN is organized by the Earth Society Foundation.^[53]

April 22 observances[link]

Growing eco-activism before Earth Day 1970[link]

In 1968, Morton Hilbert and the U.S. Public Health Service organized the Human Ecology Symposium, an environmental conference for students to hear from scientists about the effects of environmental degradation on human health.^[54] This was the beginning of Earth Day. For the next two years, Hilbert and students worked to plan the first Earth Day.^[55] In April 1970—along with a federal proclamation from U.S. Sen. Gaylord Nelson—the first Earth Day was held.^[56]

Project Survival, an early environmentalism-awareness education event, was held at Northwestern University on January 23, 1970. This was the first of several events held at university campuses across the United States in the lead-up to the first Earth Day. Also, Ralph Nader began talking about the importance of ecology in 1970.

The 1960s had been a very dynamic period for ecology in the US. Pre-1960 grassroots activism against DDT in Nassau County, New York, had inspired Rachel Carson to write her bestseller, Silent Spring (1962).

Significance of April 22[link]

Nelson chose the date in order to maximize participation on college campuses for what he conceived as an "environmental teach-in". He determined the week of April 19–25 was the best bet as it did not fall during exams or spring breaks.^[57] Moreover, it did not conflict with religious holidays such as Easter or Passover, and was late enough in spring to have decent weather. More students were likely to be in class, and there would be less competition with other mid-week events—so he chose Wednesday, April 22.

Unbeknownst to Nelson,^[58] April 22, 1970, was coincidentally the 100th anniversary of the birth of Vladimir Lenin. Time reported that some suspected the date was not a coincidence, but a clue that the event was "a Communist trick", and quoted a member of the Daughters of the American Revolution as saying, "subversive elements plan to make American children live in an environment that is good for them."^[59] J. Edgar Hoover, director of the U.S. Federal Bureau of Investigation, may have found the Lenin connection intriguing; it was alleged the FBI conducted surveillance at the 1970 demonstrations.^[60] The idea that the date was chosen to celebrate Lenin's centenary still persists in some quarters,^[61][62] an idea borne out by the similarity with the subbotnik instituted by Lenin in 1920 as days on which people would have to do community service, which typically consisted in removing rubbish from public property and collecting recyclable material. Subbotniks were also imposed on other countries within the compass of Soviet power, including Eastern Europe, and at the height of its power the Soviet Union established a nation-wide subbotnik to be celebrated on Lenin's birthday, April 22, which had been proclaimed a national holiday celebrating communism by Nikita Kruschev in 1955.

In Nebraska, Arbor Day falls on April 22, that being the birthday of Julius Sterling Morton, the founder of the national tree-planting holiday that started in 1872, which has been a legal holiday in the state since 1885. According to the National Arbor Day Foundation "the most common day for the state observances is the last Friday in April ... but a number of state Arbor Days are at other times in order to coincide with the best tree-planting weather."^[63] It has since been largely eclipsed by the more widely observed Earth Day, except in Nebraska, where it originated.

Earth Day ecology flag[link]

1969 Ecology Symbol by Ron Cobb

1969 Ecology Flag by Ron Cobb

According to Flags of the World, the Ecology Flag was created by cartoonist Ron Cobb, published on November 7, 1969, in the Los Angeles Free Press, and then placed in the public domain. The symbol, resembling the Greek letter theta, is a combination of the letters "E" and "O" taken from the words "Environment" and "Organism," respectively. The flag is patterned after thhat of the United States, with thirteen alternating-green-and-whites stripes. Its canton is green with a yellow theta. Later flags used either the ecology symbol or the peace symbol.

Earth Day anthem[link]

There are many songs that are performed on Earth Day, that generally fall into two categories. Popular songs by contemporary artists not specific to Earth Day that are under copyright or new lyrics adapted to children's songs. Creating new lyrics that are easily translated into multiple languages, and set to a universally recognized melody in the public domain, does not appear to have been attempted.

The "Earth Day Anthem" below satisfies these requirements for a universal song associated with Earth Day. Ludwig van Beethoven's "Ode to Joy" melody is already the official anthem of the European Union (in that case purely instrumental without lyrics), the melody is widely recognized and easily performed, in the public domain, and originally composed for voice. Lyrics for the Earth Day Anthem set to "Ode to Joy"^[64] are provided below:

Joyful joyful we adore our Earth in all its wonderment
Simple gifts of nature that all join into a paradise
Now we must resolve to protect her
Show her our love throughout all time
With our gentle hand and touch
We make our home a newborn world
Now we must resolve to protect her
Show her our love throughout all time
With our gentle hand and touch
We make our home a newborn world

Criticism[link]

Writer Alex Steffen, proponent of bright green environmentalism, charges that Earth Day has come to symbolize the marginalization of environmental protection, and the celebration has outlived its usefulness.^[65]

A May 5, 2009 editorial in The Washington Times contrasted Arbor Day with Earth Day, claiming that Arbor Day was a happy, non-political celebration of trees, whereas Earth Day was a pessimistic, political ideology that portrayed humans in a negative light.^[66]

The questionable nature of companies and products involved in Earth Day related promotions has led to accusations of greenwashing.^[67]

Californians for Population Stabilization (CAPS) group brings back Earth Day to human overpopulation as the main concern.^[68]

See also[link]

Environment portal

• Earth Charter
• Earth Hour

References[link]

External links[link]

Wikimedia Commons has media related to: Earth Day

Look up Earth Day in Wiktionary, the free dictionary.

Wikiquote has a collection of quotations related to: Environment

Wikinews has related news: Earth Day 2008 marked in various ways

Wikinews has related news: Earth Day 2009 celebrated around the globe

Earth Day

• Earth Day Network – Coordinating worldwide events for Earth Day.
• Earth Day Quotes
• Earth Day Event Calendar at the EnviroLink Network
• Celebrate Earth Day How to Celebrate Earth Day from WikiHow
• Earth Day 2009 Special Coverage on China Development Gateway.
• United States Earth Day – The U.S. government's Earth Day site.
• Earth Day Canada – The Canadian Official Site for Earth Day
• Earth Day at The Nature Conservancy
• Earth Day at The History Channel
• How the First Earth Day Came About by Senator Gaylord Nelson
• EPA Journal: Earth Day – an entire journal dedicated to Earth Day, written in early 1990
• Keep America Beautiful holds Earth Day cleanup activities in communities nationwide. The organization launched the famous Crying Indian campaign on Earth Day, 1971.
• "Beyond Earth Day: Fulfilling the Promise," by Gaylord Nelson, with Susan Campbell and Paul Wozniak, The University of Wisconsin Press, 2002
• Earth Week 1970 | The First Earth Day and the Earth Week Committee of Philadelphia – The history of the First Earth Day in 1970, the founding of Earth Week, and the historic events of the first Earth Week in Philadelphia
• Gaylord Nelson and Earth Day: The Making of the Modern Environmental Movement narrative account of the origins of Earth Day, Nelson's political career, as well as online access to documents from the Wisconsin Historical Society's Nelson Papers collection
• Gaylord Nelson letter outlines the origins Earth Day April 1971 to CBS President Stanton to correct TV news reporting about Earth Day's origins

Equinoctial Earth Day

• Earth Society Foundation – Official organization arranging annual equinox Earth Day celebration at the United Nations
• Who Started Earth Day – The Origins of the equinox Earth Day.

Earth Day 2010

• Billion Acts of Green (Beta) – Official Earth Day Network's "Billion Acts of Green" website for students and young adults

Earth Day 2011

• A Billion Acts of Green (®) - A "people-powered campaign to generate a billion acts of environmental service and advocacy before Rio +20" (as well as a registered trademark).

Earth Day 2012

• Earth Day 2012 - Mobilize the Earth

Earth  

"The Blue Marble" photograph of Earth, taken from Apollo 17
Designations
Alternate name(s)	Terra
Orbital characteristics
Epoch J2000.0[note 1]
Aphelion	152,098,232 km 1.01671388 AU[note 2]
Perihelion	147,098,290 km 0.98329134 AU[note 2]
Semi-major axis	149,598,261 km 1.00000261 AU[1]
Eccentricity	0.01671123[1]
Orbital period	365.256363004 days[2] 1.000017421 yr
Average orbital speed	29.78 km/s[3] 107,200 km/h
Mean anomaly	357.51716°[3]
Inclination	7.155° to Sun's equator 1.57869°[4] to invariable plane
Longitude of ascending node	348.73936°[3][note 3]
Argument of perihelion	114.20783°[3][note 4]
Satellites	1 natural (The Moon) 994 artificial (as of 31 December 2011 (2011 -12-31)[update])[5]
Physical characteristics
Mean radius	6,371.0 km[6]
Equatorial radius	6,378.1 km[7][8]
Polar radius	6,356.8 km[9]
Flattening	0.0033528[10]
Circumference	40,075.017 km (equatorial)[8] 40,007.86 km (meridional)[11][12]
Surface area	510,072,000 km2[13][14][note 5] 148,940,000 km2 land (29.2 %) 361,132,000 km2 water (70.8 %)
Volume	1.08321×1012 km3[3]
Mass	5.9736×1024 kg[3]
Mean density	5.515 g/cm3[3]
Equatorial surface gravity	9.780327 m/s2[15] 0.99732 g
Escape velocity	11.186 km/s[3]
Sidereal rotation period	0.99726968 d[16] 23h 56m 4.100s
Equatorial rotation velocity	1,674.4 km/h (465.1 m/s)[17]
Axial tilt	23°26'21".4119[2]
Albedo	0.367 (geometric)[3] 0.306 (Bond)[3]
Surface temp.    Kelvin    Celsius	min mean max 184 K[18] 287.2 K[19] 331 K[20] −89.2 °C 14 °C 57.8 °C
Atmosphere
Surface pressure	101.325 kPa (MSL)
Composition	78.08% nitrogen (N2)[3] 20.95% oxygen (O2) 0.93% argon 0.038% carbon dioxide About 1% water vapor (varies with climate)

Earth (or the Earth) is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the world, the Blue Planet,^[21] or by its Latin name, Terra.^{[note 6]}

Earth formed approximately 4.54 billion years ago by accretion from the solar nebula, and life appeared on its surface within one billion years.^[22] The planet is home to millions of species, including humans.^[23] Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land.^[24] The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. The planet is expected to continue supporting life for another 500 million to 2.3 billion years.^[25][26][27]

Earth's crust is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.

Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 365.26 solar days, or one sidereal year.^{[note 7]} The Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days).^[28] Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation. Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment.

Both the mineral resources of the planet and the products of the biosphere contribute resources that are used to support a global human population.^[29] These inhabitants are grouped into about 200 independent sovereign states (193 United Nations recognized sovereign states), which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth or in the Earth as the center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship.

Name and etymology[link]

The modern English noun earth developed from Middle English erthe (recorded in 1137), itself from Old English eorthe (dating from before 725), ultimately deriving from Proto-Germanic *erthō. Earth has cognates in all other Germanic languages, including Dutch aarde, German Erde, and Swedish, Norwegian, and Danish jord.^[30] The Earth is personified as a goddess in Germanic paganism (appearing as Jörð in Norse mythology, mother of the god Thor).^[31]

In general English usage, the name earth can be capitalized or spelled in lowercase interchangeably, either when used absolutely or prefixed with "the" (i.e. "Earth", "the Earth", "earth", or "the earth"). Many deliberately spell the name of the planet with a capital, both as "Earth" or "the Earth". This is to distinguish it as a proper noun, distinct from the senses of the term as a count noun or verb (e.g. referring to soil, the ground, earthing in the electrical sense, etc.). Oxford spelling recognizes the lowercase form as the most common, with the capitalized form as a variant of it. Another convention that is very common is to spell the name with a capital when occurring absolutely (e.g. Earth's atmosphere) and lowercase when preceded by "the" (e.g. the atmosphere of the earth). The term almost exclusively exists in lowercase when appearing in common phrases, even without "the" preceding it (e.g. "It does not cost the earth.", "What on earth are you doing?").^[32]

Chronology[link]

Artist's concept of the solar nebula

The earliest dated Solar System material was formed 4.5672 ± 0.0006 billion years ago,^[33] and by 4.54 billion years ago (within an uncertainty of 1%)^[22] the Earth and the other planets in the Solar System had formed out of the solar nebula—a disk-shaped mass of dust and gas left over from the formation of the Sun. This assembly of the Earth through accretion was thus largely completed within 10–20 million years.^[34] Initially molten, the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed shortly thereafter, 4.53 billion years ago.^[35]

The current consensus model^[36] for the formation of the Moon is the giant impact hypothesis, in which the Moon was created when a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass^[37] impacted the Earth in a glancing blow.^[38] In this model, some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to coalesce into the Moon.

Outgassing and volcanic activity produced the primordial atmosphere of the Earth. Condensing water vapor, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans.^[39] The newly formed Sun was only 70% of its present luminosity, yet evidence shows that the early oceans remained liquid—a contradiction dubbed the faint young Sun paradox. A combination of greenhouse gases and higher levels of solar activity served to raise the Earth's surface temperature, preventing the oceans from freezing over.^[40] By 3.5 billion years ago, the Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.^[41]

Two major models have been proposed for the rate of continental growth:^[42] steady growth to the present-day^[43] and rapid growth early in Earth history.^[44] Current research shows that the second option is most likely, with rapid initial growth of continental crust^[45] followed by a long-term steady continental area.^[46][47][48] On time scales lasting hundreds of millions of years, the surface continually reshaped as continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago (Ma), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 Ma, then finally Pangaea, which broke apart 180 Ma.^[49]

Evolution of life[link]

The general hypothesis is that highly energetic chemistry produced a self-replicating molecule around 4 billion years ago and half a billion years later the last common ancestor of all life existed.^[50] The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and formed a layer of ozone (a form of molecular oxygen [O₃]) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes.^[51] True multicellular organisms were formed once the cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, formerly ocean-confined life was able to colonize the land surface of Earth.^[52]

Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 Ma, during the Neoproterozoic, covered much of the planet in a sheet of ice. This hypothesis has been termed "Snowball Earth", and is of particular interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate.^[53]

Following the Cambrian explosion, about 535 Ma, there have been five major mass extinctions.^[54] The most recent such event was 65 Ma, when an asteroid impact triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared some small animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life has diversified, and several million years ago an African ape-like animal such as Orrorin tugenensis gained the ability to stand upright.^[55] This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which allowed the evolution of the human race. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had,^[56] affecting both the nature and quantity of other life forms.

The present pattern of ice ages began about 40 Ma and then intensified during the Pleistocene about 3 Ma. High-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last continental glaciation ended 10,000 years ago.^[57]

Future[link]

The life cycle of the Sun

The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 Gyr (1.1 billion years) and by 40% over the next 3.5 Gyr.^[58] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the loss of the planet's oceans.^[59]

The Earth's increasing surface temperature will accelerate the inorganic CO₂ cycle, reducing its concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 500 million^[25] to 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.^[60] After another billion years all surface water will have disappeared^[26] and the mean global temperature will reach 70 °C^[60] (158 °F). The Earth is expected to be effectively habitable for about another 500 million years from that point,^[25] although this may be extended up to 2.3 billion years if the nitrogen is removed from the atmosphere.^[27] Even if the Sun were eternal and stable, the continued internal cooling of the Earth would result in a loss of much of its CO₂ due to reduced volcanism,^[61] and 35% of the water in the oceans would descend to the mantle due to reduced steam venting from mid-ocean ridges.^[62]

The Sun, as part of its evolution, will become a red giant in about 5 Gyr. Models predict that the Sun will expand out to about 250 times its present radius, roughly 1 AU (150,000,000 km).^[58][63] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. The planet was therefore initially expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life would have been destroyed by the Sun's increased luminosity (peaking at about 5000 times its present level).^[58] A 2008 simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be vaporized.^[63]

Composition and structure[link]

Size comparison of inner planets (left to right): Mercury, Venus, Earth and Mars

Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter. It is the largest of the four solar terrestrial planets in size and mass. Of these four planets, Earth also has the highest surface gravity, the strongest magnetic field, and fastest rotation,^[64] and is probably the only one with active plate tectonics.^[65] It also has the highest density in the Solar System at 5.515 g/cm³, slightly more than Mercury’s density of 5.427 g/cm³. ^[66]

Shape[link]

Chimborazo, Ecuador is the furthermost point on the Earth's surface from its center.^[67]

The shape of the Earth approximates an oblate spheroid, a sphere flattened along the axis from pole to pole such that there is a bulge around the equator.^[68] This bulge results from the rotation of the Earth, and causes the diameter at the equator to be 43 km larger than the pole-to-pole diameter.^[69] The average diameter of the reference spheroid is about 12,742 km, which is approximately (40,000/π) km, as the meter was originally defined as 1/10,000,000 of the distance from the Equator to the North Pole through Paris, France.^[70] Local topography deviates from this idealized spheroid, although on a global scale, these deviations are small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls.^[71] The largest local deviations in the rocky surface of the Earth are Mount Everest (8848 m above local sea level) and the Mariana Trench (10,911 m below local sea level). Because of the equatorial bulge, the surface locations farthest from the center of the Earth are the summits of Mount Chimborazo in Ecuador and Huascarán in Peru.^[72][73][74]

Chemical composition[link]

The mass of the Earth is approximately 5.98×10²⁴ kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation, the core region is estimated to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.^[76]

Nearly 47% of the Earth's crust by weight consists of oxygen and another 27% of silicon. Other elements, in descending order, are aluminum (8.1%), iron (5.0%), sodium (2.8%), potassium (2.6%), and magnesium (2.1%) with all other elements accounting for the remaining 1.5%. As the table on the right shows, the more common rock constituents of the Earth's crust are nearly all oxides, with 11 oxides making up 99% of the weight. The principal oxides are silica, alumina, iron oxides, lime, magnesia, potash, and soda. The silica functions principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature; silicates make up 95% of the crust by weight.^[77]

Internal structure[link]

The interior of the Earth is divided into layers, which are defined by their chemical or physical (rheological) properties. The outer layer of the Earth is a solid crust made of silicate. The thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents. Under the crust is a highly viscous solid mantle. Between the crust and the mantle is a thin layer known as the Mohorovičić discontinuity. The crust and the upper mantle are collectively known as the lithosphere. The lithosphere rides on top of a portion of the mantle known as the asthenosphere, which has a lower viscosity than the rest of the mantle. There is a transition zone where the upper mantle and the mantle meet at between 410 and 660 km. Geologists believe that matter in the transition zone undergoes significant changes due to increasing pressure, rearranging its atoms into crystal structures. Beneath the mantle, an extremely low viscosity liquid outer core surrounds the solid inner core.^[78] The inner core may rotate at a slightly higher rate than the remainder of the planet, advancing by 0.1–0.5° per year.^[79]

Geologic layers of the Earth^[80]

Earth cutaway from core to exosphere. Not to scale.	Depth[81] km	Component Layer	Density >g/cm3
	0 - 60	Lithosphere[note 8]	—
	0 - 35	Crust[note 9]	2.2 - 2.9
	35 - 60	Upper mantle	3.4 - 4.4
	35 - 2890	Mantle	3.4 - 5.6
	100 - 700	Asthenosphere	—
	2890 - 5100	Outer core	9.9 - 12.2
	5100 - 6378	Inner core	12.8 - 13.1

Heat[link]

Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%).^[82] The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232.^[83] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.^[84] Because much of the heat is provided by radioactive decay, scientists surmise that early in Earth history, before isotopes with short half-lives had been depleted, Earth's heat production would have been much higher. This extra heat production, twice present-day at approximately 3 billion years ago,^[82] would have increased temperature gradients within the Earth, increasing the rates of mantle convection and plate tectonics, and allowing the production of igneous rocks such as komatiites that are not formed today.^[85]

Note that the total heat released by any isotope includes the total energy released in its decay chain; for example, the U²³⁸ entry includes the contribution from U²³⁴ as well.

The mean heat loss from the Earth is 87 mW m⁻², for a global heat loss of 4.42 × 10¹³ W.^[87] A portion of the core's thermal energy is transported toward the crust by mantle plumes; a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts.^[88] More of the heat in the Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs in the oceans because the crust there is much thinner than that of the continents.^[89]

Tectonic plates[link]

Earth's main plates^[90]

Plate name	Area 106 km2
Pacific Plate	103.3
African Plate[note 10]	78.0
North American Plate	75.9
Eurasian Plate	67.8
Antarctic Plate	60.9
Indo-Australian Plate	47.2
South American Plate	43.6

The mechanically rigid outer layer of the Earth, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: Convergent boundaries, at which two plates come together, Divergent boundaries, at which two plates are pulled apart, and Transform boundaries, in which two plates slide past one another laterally. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries.^[91] The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates,^[92] and their motion is strongly coupled with convection patterns inside the Earth's mantle.

As the tectonic plates migrate across the planet, the ocean floor is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes continually recycles the oceanic crust back into the mantle. Because of this recycling, most of the ocean floor is less than 100 million years in age. The oldest oceanic crust is located in the Western Pacific, and has an estimated age of about 200 million years.^[93][94] By comparison, the oldest dated continental crust is 4030 million years old.^[95]

The seven major plates are the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American. Other notable plates include the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and 55 million years ago. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/year^[96] and the Pacific Plate moving 52–69 mm/year. At the other extreme, the slowest-moving plate is the Eurasian Plate, progressing at a typical rate of about 21 mm/year.^[97]

Surface[link]

The Earth's terrain varies greatly from place to place. About 70.8%^[98] of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes,^[69] oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains. The remaining 29.2% not covered by water consists of mountains, deserts, plains, plateaus, and other geomorphologies.

The planetary surface undergoes reshaping over geological time periods because of tectonics and erosion. The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects. Glaciation, coastal erosion, the build-up of coral reefs, and large meteorite impacts^[99] also act to reshape the landscape.

Present-day Earth altimetry and bathymetry. Data from the National Geophysical Data Center's TerrainBase Digital Terrain Model.

The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors.^[100] Sedimentary rock is formed from the accumulation of sediment that becomes compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form only about 5% of the crust.^[101] The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. The most abundant silicate minerals on the Earth's surface include quartz, the feldspars, amphibole, mica, pyroxene and olivine.^[102] Common carbonate minerals include calcite (found in limestone) and dolomite.^[103]

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. Currently the total arable land is 13.31% of the land surface, with only 4.71% supporting permanent crops.^[14] Close to 40% of the Earth's land surface is presently used for cropland and pasture, or an estimated 1.3×10⁷ km² of cropland and 3.4×10⁷ km² of pastureland.^[104]

The elevation of the land surface of the Earth varies from the low point of −418 m at the Dead Sea, to a 2005-estimated maximum altitude of 8,848 m at the top of Mount Everest. The mean height of land above sea level is 840 m.^[105]

Hydrosphere[link]

Elevation histogram of the surface of the Earth

The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from others in the Solar System. The Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m. The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean with a depth of −10,911.4 m.^{[note 11][106]}

The mass of the oceans is approximately 1.35×10¹⁸ metric tons, or about 1/4400 of the total mass of the Earth. The oceans cover an area of 3.618×10⁸ km² with a mean depth of 3,682 m, resulting in an estimated volume of 1.332×10⁹ km³.^[107] If all the land on Earth were spread evenly, water would rise to an altitude of more than 2.7 km.^{[note 12]} About 97.5% of the water is saline, while the remaining 2.5% is fresh water. Most fresh water, about 68.7%, is currently ice.^[108]

The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water (35 ‰).^[109] Most of this salt was released from volcanic activity or extracted from cool, igneous rocks.^[110] The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.^[111] Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir.^[112] Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño-Southern Oscillation.^[113]