U.S. Sen. Gaylord Nelson, a Wisconsin native, is largely credited for organizing the first Earth Day in spring 1970, when it was still legal for factories to spew noxious fumes into the air or dump toxic waste into streams. That's because the U.S. Environmental Protection Agency didn't exist yet, and there were no laws to protect the environment.
Nelson recruited Harvard University professor Denis Hayes to coordinate and promote Earth Day nationally. The event was a success.
Twenty million Americans took to the streets on April 22, 1970, demanding action on environmental pollution. That December, Congress authorized the establishment of a new federal agency, the EPA, to ensure environmental protection.
"Unfortunately, human beings have irrevocably upset the balance of nature and, as a result, the world is facing the greatest rate of extinction since we lost the dinosaurs more than 60 million years ago," the organization states on its website.
Climate change, deforestation, habitat loss, trafficking and poaching, unsustainable agriculture, pollution and pesticide are just some of the devastating factors that have led to the loss of species.
Which species are declining?
Earth is facing a "mass extinction" of all species of mammals, birds, reptiles, amphibians, arthropods, fish, crustaceans, corals and other cnidarians, and plants, with between one and five species going extinct every year, according to the Earth Day Network.
Additionally, Earth Day Network notes:
Insect populations have decreased by more than 75% in Germany over the last 28 years, which is "alarming" because 80% of wild plants rely on bees and other insects for pollination, and 60% of bird species rely on insects for food.
Primates are also under "extraordinary threat," with close to 60% of the world's 504 primate species under threat of extinction and 80% in "severe population decline."
In the past 20 years, by-catch from global fishing operations has affected 75% of all toothed whale species, such as dolphins and porpoises, 65% of baleen whale species, such as humpback and blue whales and 65% of pinniped species, such as sea lions.
In addition, 40% of the world's bird population is in decline, with 1 in 8 species threatened with global extinction.
Big cats, such as leopards, tigers and cheetahs, are in "critical decline," and many will become extinct in the next 10 years. They are often exploited for their body parts and skins, and China retains the biggest market for these items.
Lizard populations are "especially vulnerable" to climate change, according to the organization. If the current decline continues, 40% of lizards will become extinct by 2080.
The American Bison, which one roamed from Alaska to New Mexico in the millions, now occupy less than 1% of their original habitat. The species is now compared to herded cattle due to its "small and tightly controlled" habitat.
What are goals of this year's Earth Day theme?
The rapid rate of extinction can still be slowed, and many declining, threatened and endangered species can be recovered, according to the Earth Day Network.
Educate people about the accelerating rate of extinction of millions as well as raise awareness on what is causing it.
Create change via policies that protect broad groups of species as well as individual species and their habitats.
Build a global movement that embraces nature.
Encourage the alteration of individual habits, such as developing plant-based diets and eliminating the use of pesticides and herbicides.
All living species have intrinsic value and play a specific role in the circle of life, according to the organization, which hopes to build a united movement of consumers, voters, educators, faith leaders and scientists to demand immediate action.