Earth

== Cultural and historical viewpoint ==
{{Main|Earth in culture|Earth in science fiction}}
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|alt=Woman seeing the Earth from space through a window|thumb|[[Tracy Caldwell Dyson]], a [[NASA]] astronaut, observing Earth from the [[Cupola (ISS module)|''Cupola'' module]] at the [[International Space Station]] on 11 September 2010]]
[[Culture|Human cultures]] have developed many views of the planet.<ref name="NYT-20181224b">{{cite news |last=Widmer |first=Ted |author-link=Edward L. Widmer|title=What Did Plato Think the Earth Looked Like? – For millenniums, humans have tried to imagine the world in space. Fifty years ago, we finally saw it. |url=https://www.nytimes.com/2018/12/24/opinion/plato-earth-christmas-eve-apollo-8.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/12/24/opinion/plato-earth-christmas-eve-apollo-8.html |archive-date=1 January 2022 |url-access=limited |date=24 December 2018 |work=[[The New York Times]] |access-date=25 December 2018}}{{cbignore}}</ref> The standard [[astronomical symbols]] of Earth are a quartered circle, [[File:Earth symbol (fixed width).svg|🜨]],<ref name="liungman2004" /> representing the [[four corners of the world]], and a [[globus cruciger]], [[File:globus cruciger (fixed width).svg|♁]]. Earth is sometimes [[Personification|personified]] as a [[deity]]. In many cultures it is a [[mother goddess]] that is also the primary [[fertility deity]].<ref name="Stookey-2004">{{Cite book |title=Thematic Guide to World Mythology |last=Stookey |first=Lorena Laura |publisher=Greenwood Press |year=2004 |isbn=978-0-313-31505-3 |location=Westport, CN |pages=[https://archive.org/details/thematicguidetow00lore/page/114 114–115] |url=https://archive.org/details/thematicguidetow00lore/page/114}}</ref> [[Creation myth]]s in many religions involve the creation of Earth by a supernatural deity or deities.<ref name="Stookey-2004" /> The [[Gaia hypothesis]], developed in the mid-20th century, compared Earth's environments and life as a single self-regulating organism leading to broad stabilization of the conditions of habitability.<ref>{{cite book|last1=Lovelock|first1=James E.|author-link=James Lovelock|title=The Vanishing Face of Gaia |publisher=Basic Books|year=2009|page=255|isbn=978-0-465-01549-8}}</ref><ref>{{cite journal|last=Lovelock|first=James E.|author-link=James Lovelock |year=1972 |title=Gaia as seen through the atmosphere|journal=Atmospheric Environment |volume=6|issue=8 |pages=579–580|bibcode=1972AtmEn...6..579L |doi=10.1016/0004-6981(72)90076-5 |issn=1352-2310}}</ref><ref>{{Cite journal |last1=Lovelock |first1=J.E. |last2=Margulis |first2=L. |author2-link=Lynn Margulis |date=1974 |title=Atmospheric homeostasis by and for the biosphere: the gaia hypothesis |journal=Tellus A |volume=26 |issue=1–2 |pages=2–10 |doi=10.3402/tellusa.v26i1-2.9731 |doi-access=free |s2cid=129803613 |language=en |bibcode=1974Tell...26....2L }}</ref>

[[Timeline of first images of Earth from space|Images of Earth taken from space]], particularly during the Apollo program, have been credited with altering the way that people viewed the planet that they lived on, called the [[overview effect]], emphasizing its beauty, uniqueness and apparent fragility.<ref>{{cite news|last=Overbye|first=Dennis|author-link=Dennis Overbye|date=21 December 2018|title=Apollo 8's Earthrise: The Shot Seen Round the World – Half a century ago today, a photograph from the moon helped humans rediscover Earth.|work=[[The New York Times]]|url=https://www.nytimes.com/2018/12/21/science/earthrise-moon-apollo-nasa.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/12/21/science/earthrise-moon-apollo-nasa.html |archive-date=1 January 2022 |url-access=limited|access-date=24 December 2018}}{{cbignore}}</ref><ref>{{cite news|last1=Boulton|first1=Matthew Myer|last2=Heithaus|first2=Joseph|date=24 December 2018|title=We Are All Riders on the Same Planet – Seen from space 50 years ago, Earth appeared as a gift to preserve and cherish. What happened?|work=[[The New York Times]] |url=https://www.nytimes.com/2018/12/24/opinion/earth-space-christmas-eve-apollo-8.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/12/24/opinion/earth-space-christmas-eve-apollo-8.html |archive-date=1 January 2022 |url-access=limited|access-date=25 December 2018}}{{cbignore}}</ref> In particular, this caused a realization of the scope of effects from human activity on Earth's environment. Enabled by science, particularly [[Earth observation]],<ref>{{cite web |title=ESPI Evening Event "Seeing Our Planet Whole: A Cultural and Ethical View of Earth Observation" |website=ESPI – European Space Policy Institute |date=7 October 2021 |url=https://espi.or.at/news/espi-evening-event-seeing-our-planet-whole-a-cultural-and-ethical-view-of-earth-observation |access-date=27 January 2022}}</ref> humans have started to take [[Environmentalism|action on environmental issues]] globally,<ref>{{cite web |title=Two early images of Earth that bolstered the environmental movement – CBC Radio |website=CBC |date=16 April 2020 |url=https://www.cbc.ca/radio/quirks/two-early-images-of-earth-that-bolstered-the-environmental-movement-1.5534843 |access-date=27 January 2022}}</ref> acknowledging the impact of humans and the [[Ecological network|interconnectedness of Earth's environments]].

Scientific investigation has resulted in several culturally transformative shifts in people's view of the planet. Initial belief in a [[flat Earth]] was gradually displaced in [[Ancient Greece]] by the idea of a [[spherical Earth]], which was attributed to both the philosophers [[Pythagoras]] and [[Parmenides]].<ref>{{cite book |last=Kahn |first=Charles H. | author-link = Charles H. Kahn |date=2001 |title=Pythagoras and the Pythagoreans: A Brief History |url={{GBurl|id=GKUtAwAAQBAJ|q=Pythagoreanism|p=72}} |location=Indianapolis, IN and Cambridge, England |publisher=Hackett Publishing Company |isbn=978-0-87220-575-8 |page=53}}</ref><ref>{{Cite book |last=Garwood|first=Christine|url=https://www.worldcat.org/oclc/184822945|title=Flat earth : the history of an infamous idea|date=2008|publisher=Thomas Dunne Books |isbn=978-0-312-38208-7 |edition=1st|location=New York|oclc=184822945|pages=26–31}}</ref> Earth was generally believed to be [[Geocentric model|the center of the universe]] until the 16th century, when scientists first concluded that it was [[heliocentrism|a moving object]], one of the planets of the Solar System.<ref name="arnett20060716" />

It was only during the 19th century that geologists realized [[Earth's age]] was at least many millions of years.<ref>{{Cite book |title=Physical Geology: Exploring the Earth |last1=Monroe |first1=James |publisher=Thomson Brooks/Cole |year=2007 |isbn=978-0-495-01148-4 |pages=263–265 |last2=Wicander |first2=Reed |last3=Hazlett |first3=Richard}}</ref> [[Lord Kelvin]] used [[thermodynamics]] to estimate the age of Earth to be between 20 million and 400&nbsp;million years in 1864, sparking a vigorous debate on the subject; it was only when radioactivity and [[Radiometric dating|radioactive dating]] were discovered in the late 19th and early 20th centuries that a reliable mechanism for determining Earth's age was established, proving the planet to be billions of years old.<ref>{{Cite book |title=An Equation for Every Occasion: Fifty-Two Formulas and Why They Matter |last=Henshaw |first=John M. |publisher=Johns Hopkins University Press |year=2014 |isbn=978-1-4214-1491-1 |pages=117–118}}</ref><ref>{{Cite book |title=Lord Kelvin and the Age of the Earth |last=Burchfield |first=Joe D. |publisher=University of Chicago Press |year=1990 |isbn=978-0-226-08043-7 |pages=13–18}}</ref>