Earth: Difference between revisions

{{Use dmy dates|date=April 2018}}{{Use American English|date=July 2015}}

This infobox has been formatted in the same way as those for other Solar System

planets and bodies, so please do not change it without discussion on the talkpage.

---------------------------------------------------------------------------------------->|background=#f8f9fa|name=Earth|adjectives=Earthly, terrestrial, terran, tellurian|symbol=[[File:Earth symbol (small, bold).svg|24px|alt=🜨|Astronomical symbol of Earth]]|image=The Blue Marble (remastered).jpg|image_alt="[[The Blue Marble]]" photograph of Earth taken by the ''[[Apollo 17]]'' mission. The Arabian peninsula, Africa and Madagascar lie in the upper half of the disc, whereas Antarctica is at the bottom.|caption=''[[The Blue Marble]]'', the first full-view photograph of the planet <br/>  taken by [[Apollo 17]] [[astronaut]]s in 1972|alt_names=<!--{{Unbulleted list|style=padding-top:0.1em;|li_style=line-height:1.3em; |{{hlist|the Earth|the World}} |{{hlist|Blue Planet|[[The Blue Marble|Blue Marble]]|''[[Terra]]''|[[Gaia (mythology)|Gaia]]}} }}-->|epoch=[[J2000.0|J2000]]<ref name="epoch">All astronomical quantities vary, both in time (secularly) and frequency (periodically). The quantities given are the values at the instant [[J2000.0]] of the secular variation, ignoring all periodic variations.</ref>|aphelion={{convert|152100000|km|mi AU|comma=gaps|abbr=on|disp=x|<ref name="apsis">aphelion = ''a'' × (1 + ''e''); perihelion = ''a'' × (1&nbsp;– ''e''), where ''a'' is the semi-major axis and ''e'' is the eccentricity. The difference between Earth's perihelion and aphelion is 5 million kilometers.</ref><br /><small>(|)</small>}}|perihelion={{convert|147095000|km|mi AU|comma=gaps|abbr=on|disp=x|<ref name="apsis" /><br /><small>(|)</small>}}|semimajor={{convert|149598023|km|mi AU|comma=gaps|abbr=on|disp=x|<ref name="VSOP87">{{cite journal |title=Numerical expressions for precession formulae and mean elements for the Moon and planets |journal=Astronomy and Astrophysics |volume=282 |issue=2 |pages=663–83 |date=February 1994 |last1=Simon |first1=J.L. |last2=Bretagnon |first2=P. |last3=Chapront |first3=J. |last4=Chapront-Touzé |first4=M. |last5=Francou |first5=G. |last6=Laskar |first6=J. |bibcode=1994A&A...282..663S}}</ref><br /><small>(|)</small>}}|eccentricity={{val|0.0167086}}<ref name="VSOP87" />|period={{convert|365.256363004|d|years|comma=gaps|abbr=on|lk=out|disp=x|<ref name="IERS"/><br /><small>(|)</small>}}|avg_speed={{convert|29.78|km/s|km/h mph|comma=gaps|abbr=on|disp=x|<ref name="earth_fact_sheet">{{cite web |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html |title=Earth Fact Sheet |publisher=NASA/Goddard Space Flight Center |first=David R. |last=Williams |date=16 March 2017 |accessdate=26 July 2018}}</ref><br /><small>(|)</small>}}|mean_anomaly={{val|358.617|u=°}}|inclination={{Unbulleted list|class=nowrap |{{val|7.155|u=°}} to the [[Sun]]'s [[equator]]; |{{val|1.57869|u=°}}<ref name="Allen294">{{cite book| last1 = Allen| first1 = Clabon Walter| last2 = Cox| first2 = Arthur N.| title = Allen's Astrophysical Quantities| url = https://books.google.com/books?id=w8PK2XFLLH8C&pg=PA294| accessdate = 13 March 2011| date = 2000| publisher = Springer| isbn = 978-0-387-98746-0| page = 294 }}</ref> to [[invariable plane]]; |{{val|0.00005|u=°}} to J2000 [[ecliptic]]}}|asc_node={{val|-11.26064|u=°}}<ref name="earth_fact_sheet" /> to J2000 ecliptic|arg_peri={{val|114.20783|u=°}}<ref name="earth_fact_sheet" />|satellites={{unbulleted list

| 1 natural satellite: the [[Moon]]

| 5 [[quasi-satellite]]s

| >1 800 operational [[artificial satellite]]s<ref name="ucs">{{cite web |url=https://www.ucsusa.org/nuclear-weapons/space-weapons/satellite-database |title=UCS Satellite Database |work=Nuclear Weapons & Global Security |publisher=Union of Concerned Scientists |date=10 August 2018 |accessdate=27 September 2018}}</ref>

| >16 000 [[space debris]]<ref name="space_debris">As of 4 January 2018, the United States Strategic Command tracked a total of 18,835 artificial objects, mostly debris. See: {{cite journal |url=https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv22i1.pdf |title=Satellite Box Score |journal=Orbital Debris Quarterly News |editor1-first=Phillip |editor1-last=Anz-Meador |editor2-first=Debi |editor2-last=Shoots |volume=22 |issue=1 |page=12 |date=February 2018 |accessdate=18 April 2018}}</ref>

}}|allsatellites=yes|mean_radius={{convert|6371.0|km|mi|comma=gaps|abbr=on|disp=x| <small>(|)</small>}}<ref name="hbcp2000">{{cite book| last = Lide| first = David R.| title = Handbook of Chemistry and Physics| url = https://archive.org/details/crchandbookofche0000unse_u9i8| edition = 81st| date = 2000| publisher = CRC| isbn = 978-0-8493-0481-1| editor = David R. Lide }}</ref>|equatorial_radius={{convert|6378.1|km|mi|comma=gaps|abbr=on|disp=x| <small>(|)</small>}}<ref name="usno">{{cite web |title=Selected Astronomical Constants, 2011 |work=The Astronomical Almanac |url=http://asa.usno.navy.mil/SecK/2011/Astronomical_Constants_2011.txt |archiveurl=https://web.archive.org/web/20130826043456/http://asa.usno.navy.mil/SecK/2011/Astronomical_Constants_2011.txt |archivedate=26 August 2013 |accessdate=25 February 2011}}</ref><ref name="WGS-84"/>|polar_radius={{convert|6356.8|km|mi|comma=gaps|abbr=on|disp=x| <small>(|)</small>}}<ref name="cazenave_ahrens1995">{{cite book |first1=Anny |last1=Cazenave |editor=Ahrens, Thomas J |date=1995 |title=Global Earth Physics: A Handbook of Physical Constants |journal=Global Earth Physics: A Handbook of Physical Constants |issue=1 |publisher=American Geophysical Union |location=Washington, DC |isbn=978-0-87590-851-9 |chapter-url=http://www.agu.org/reference/gephys/5_cazenave.pdf |archiveurl=https://web.archive.org/web/20061016024803/http://www.agu.org/reference/gephys/5_cazenave.pdf |archivedate=16 October 2006 |accessdate=3 August 2008 |chapter=Geoid, Topography and Distribution of Landforms|series=AGU Reference Shelf |volume=1 |doi=10.1029/RF001 |bibcode=1995geph.conf.....A }}</ref>|flattening={{val|0.0033528}}<ref name="IERS2004">{{cite book| author = International Earth Rotation and Reference Systems Service (IERS) Working Group| others = Dennis D. McCarthy, Gérard Petit, IERS Convertions Centre| editor-last = McCarthy| editor-first = Dennis D.| editor2-last = Petit| editor2-first = Gérard| title = IERS Conventions (2003| url = http://www.iers.org/SharedDocs/Publikationen/EN/IERS/Publications/tn/TechnNote32/tn32.pdf?__blob=publicationFile&v=1| format = PDF| accessdate = 29 April 2016| year = 2004| publisher = Verlag des Bundesamts für Kartographie und Geodäsie| location = Frankfurt am Main| isbn = 978-3-89888-884-4| page = 12| chapter = General Definitions and Numerical Standards| chapter-url = http://www.iers.org/SharedDocs/Publikationen/EN/IERS/Publications/tn/TechnNote32/tn32_009.pdf?__blob=publicationFile&v=1| work = IERS Technical Note No. 32 }}</ref><br />1/{{val|298.257222101}} ([[ETRS89]])|circumference={{unbulleted list |class=nowrap

| {{convert|40075.017|km|mi|comma=gaps|abbr=on|disp=x| <small>[[equator]]ial (|)</small>}}<ref name="WGS-84">[[World Geodetic System]] (''WGS-84''). [http://earth-info.nga.mil/GandG/wgs84/ Available online] {{Webarchive|url=https://web.archive.org/web/20200311023739/https://earth-info.nga.mil/GandG/wgs84/ |date=2020-03-11 }} from [[National Geospatial-Intelligence Agency]].</ref>

| {{convert|40007.86|km|mi|comma=gaps|abbr=on|disp=x| <small>[[meridional]] (|)</small>}}<ref name="WGS-84-2">{{cite web |first1=Sigurd |last1=Humerfelt |date=26 October 2010 |title=How WGS 84 defines Earth |url=http://home.online.no/~sigurdhu/WGS84_Eng.html |accessdate=29 April 2011 |url-status=dead |archiveurl=https://web.archive.org/web/20110424104419/http://home.online.no/~sigurdhu/WGS84_Eng.html |archivedate=24 April 2011 }}</ref><ref name="circ">Earth's [[circumference]] is almost exactly 40,000&nbsp;km because the metre was calibrated on this measurement—more specifically, 1/10-millionth of the distance between the poles and the equator.</ref>

}}|surface_area={{unbulleted list |class=nowrap

| {{convert|510072000|km2|sqmi|comma=gaps|abbr=on|disp=x| <small>(|)</small>}}<ref name="Pidwirny 2006_8">{{cite journal |last1=Pidwirny |first1=Michael |date=2 February 2006 |title=Surface area of our planet covered by oceans and continents.(Table 8o-1) |publisher=University of British Columbia, Okanagan |url=http://www.physicalgeography.net/fundamentals/8o.html |accessdate=26 November 2007}}</ref><ref name="cia">{{cite web |author=Staff |date=24 July 2008 |url=https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html |title=World |work=The World Factbook |publisher=Central Intelligence Agency |accessdate=5 August 2008 |archive-date=5 January 2010 |archive-url=https://web.archive.org/web/20100105171656/https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html |url-status=dead }}</ref><ref name="surfacecover">Due to natural fluctuations, ambiguities surrounding [[Ice shelf|ice shelves]], and mapping conventions for [[vertical datum]]s, exact values for land and ocean coverage are not meaningful. Based on data from the [[Vector Map]] and [http://www.landcover.org/ Global Landcover] {{Webarchive|url=https://web.archive.org/web/20150326085837/http://www.landcover.org/ |date=2015-03-26 }} datasets, extreme values for coverage of lakes and streams are 0.6% and 1.0% of Earth's surface. The ice shields of [[Antarctica]] and [[Greenland]] are counted as land, even though much of the rock that supports them lies below sea level.</ref>

| {{convert|148940000|km2|sqmi|comma=gaps|abbr=on|disp=x| land <small>(|; 29.2%)</small>}}

| {{convert|361132000|km2|sqmi|comma=gaps|abbr=on|disp=x| water <small>(|; 70.8%)</small>}}

}}|volume=260 billion cubic miles <ref name="devansh">{{cite web |url= https://factshungry.com/mind-blowing-facts-about-earth/| title= Earth's facts| date= 10 May 2021| publisher= factshungry}}</ref>|mass={{val|5.97237|e=24|u=kg}} <small>({{val|1.31668|e=25|u=lb}})</small><ref name="Luzum2011">{{cite journal |last1=Luzum |first1=Brian |last2=Capitaine |first2=Nicole |last3=Fienga |first3=Agnès |last4=Folkner |first4=William |last5=Fukushima |first5=Toshio |last6=Hilton |first6=James |last7=Hohenkerk |first7=Catherine |last8=Krasinsky |first8=George |last9=Petit |first9=Gérard |last10=Pitjeva |first10=Elena |last11=Soffel |first11=Michael |last12=Wallace |first12=Patrick |display-authors=5 |title=The IAU 2009 system of astronomical constants: The report of the IAU working group on numerical standards for Fundamental Astronomy |journal=Celestial Mechanics and Dynamical Astronomy |volume=110 |issue=4 |date=August 2011 |pages=293–304 |bibcode=2011CeMDA.110..293L |doi=10.1007/s10569-011-9352-4|s2cid=122755461 }}</ref> <br /> <small>({{val|3.0|e=-6|ul=solar mass}})</small>|density={{convert|5.514|g/cm3|lb/cuin|comma=gaps|abbr=on|disp=x| <small>(|)</small>}}<ref name="earth_fact_sheet" />|surface_grav={{convert|9.807|m/s2|ft/s2|comma=gaps|abbr=on|disp=x| <small>([[Gravity of Earth|{{val|1|u=''g''}}]]; |)</small>}}<ref name="NIST2008">{{cite book |url=http://physics.nist.gov/Pubs/SP330/sp330.pdf |title=The international system of units (SI) |publisher=United States Department of Commerce, National Institute of Standards and Technology Special Publication 330 |edition=2008 |page=52 |access-date=2019-06-13 |archive-date=2016-06-03 |archive-url=https://web.archive.org/web/20160603215953/http://physics.nist.gov/Pubs/SP330/sp330.pdf |url-status=dead }}</ref>|moment_of_inertia_factor=0.3307<ref name="Williams1994">{{cite journal |last1=Williams |first1=James G. |title=Contributions to the Earth's obliquity rate, precession, and nutation |journal=The Astronomical Journal |volume=108 |year=1994 |page=711 |issn=0004-6256 |doi=10.1086/117108 |bibcode=1994AJ....108..711W}}</ref>|escape_velocity={{convert|11.186|km/s|km/h mph|comma=gaps|abbr=on|disp=x|<ref name="earth_fact_sheet" /> <br /> <small>(|)</small>}}|sidereal_day={{longitem|{{val|0.99726968|u=d}}<ref name="Allen296">{{cite book| last1 = Allen| first1 = Clabon Walter| last2 = Cox| first2 = Arthur N.| title = Allen's Astrophysical Quantities| url = https://books.google.com/books?id=w8PK2XFLLH8C&pg=PA296| accessdate = 17 August 2010| date = 2000| publisher = Springer| isbn = 978-0-387-98746-0| page = 296 }}</ref> <br /> <small>(23h&nbsp;56m&nbsp;4.100s)</small>}}|rot_velocity={{convert|1674.4|km/h|km/s km/h mph|order=out|comma=gaps|abbr=on|disp=x|<ref name="Cox2000">{{cite book| last1 = Allen| first1 = Clabon Walter| last2 = Cox| first2 = Arthur N.| title = Allen's Astrophysical Quantities| url = https://books.google.com/books?id=w8PK2XFLLH8C&pg=PA244| accessdate = 17 August 2010| edition = 4th| date = 2000| publisher = AIP Press| location = New York| isbn = 978-0-387-98746-0| page = 244| editor = Arthur N. Cox }}</ref> <br /> <small>(|)</small>}}|axial_tilt={{val|23.4392811|u=°}}<ref name="IERS"/>|albedo={{Unbulleted list|class=nowrap |0.367 [[Geometric albedo|geometric]]<ref name="earth_fact_sheet" /> |0.306 [[Bond albedo|Bond]]<ref name="earth_fact_sheet" />}}|atmosphere=yes|temp_name1=[[Kelvin]]|min_temp_1=184&nbsp;K<ref name="asu_lowest_temp">{{cite web |url=http://wmo.asu.edu/world-lowest-temperature |title=World: Lowest Temperature |work=[[WMO]] Weather and Climate Extremes Archive |publisher=[[Arizona State University]] |accessdate=7 August 2010 |url-status=dead |archiveurl=https://web.archive.org/web/20100616025722/http://wmo.asu.edu/world-lowest-temperature |archivedate=16 June 2010 }}</ref>|mean_temp_1=288&nbsp;K<ref name="kinver20091210">{{cite news |url=http://news.bbc.co.uk/2/hi/science/nature/8406839.stm |title=Global average temperature may hit record level in 2010 |last1=Kinver |first1=Mark |date=10 December 2009 |publisher=BBC |accessdate=22 April 2010}}</ref>|max_temp_1=330&nbsp;K<ref name="asu_highest_temp">{{cite web |url=http://wmo.asu.edu/world-highest-temperature |title=World: Highest Temperature |work=[[WMO]] Weather and Climate Extremes Archive |publisher=[[Arizona State University]] |accessdate=7 August 2010 |url-status=dead |archiveurl=https://web.archive.org/web/20130104143844/http://wmo.asu.edu/world-highest-temperature |archivedate=4 January 2013 |df=dmy}}</ref>|temp_name2=Celsius|min_temp_2=−89.2&nbsp;°C|mean_temp_2=14.9&nbsp;°C|max_temp_2=56.9&nbsp;°C|temp_name3=Fahrenheit|min_temp_3=−128.5&nbsp;°F|mean_temp_3=58.7&nbsp;°F|max_temp_3=134.3&nbsp;°F|surface_pressure={{val|101.325|ul=kPa}} (at [[Sea level|MSL]])|atmosphere_composition={{unbulleted list |class=nowrap

}}|note=no}}

'''Earth'''<!-- is the [[planet]] we live on. It--> is the third [[planet]] from the [[Sun]] in the [[Solar System]]. It is the only planet known to have [[life]] on it. The Earth [[Age of the Earth|formed about 4.5 billion years ago]].<ref name="age earth">{{cite journal|url=http://sp.lyellcollection.org/cgi/content/abstract/190/1/205|title=The age of the Earth in the twentieth century: a problem (mostly) solved|year=2001 |accessdate=2009-07-28|journal=Geological Society, London, Special Publications|doi=10.1144/GSL.SP.2001.190.01.14 |last1=Dalrymple |first1=G. Brent |volume=190 |pages=205–221 |bibcode=2001GSLSP.190..205D |s2cid=130092094 }}</ref><ref>Dalrymple G. Brent 2004. ''Ancient Earth, ancient skies: the age of Earth and its cosmic surroundings''. Stanford. p26, table 3.1</ref> It is one of four [[terrestrial planet|rocky planets]] on the inner side of the [[Solar System]]. The other three are [[Mercury (planet)|Mercury]], [[Venus]], and [[Mars (planet)|Mars]].

The large [[mass]] of the Sun keeps the Earth in [[orbit]] through the force of [[gravity]].<ref>See [[Formation and evolution of the Solar System]] for an account</ref> Earth also turns around in space, so that different parts face the Sun at different times. Earth goes around the Sun once (one [[year]]) for every 365{{Frac|4}} times it turns around (one [[day]]).

Earth is the only [[planet]] in the Solar System that has a large amount of [[liquid]] [[water]] on its surface.<ref>name="Gomes">{{cite journal | url=http://www.nature.com/nature/journal/v435/n7041/pdf/nature03676.pdf | title=Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets | author=R. Gomes H.F. |display-authors = etal | journal=Nature | year=2005 | volume=435 | pages=466–469 | doi=10.1038/nature03676| pmid=15917802 | issue=7041| bibcode=2005Natur.435..466G | s2cid=4398337 }}</ref><ref>{{cite journal | author= A. Morbidelli J. |display-authors = etal | title= Source regions and timescales for the delivery of water to the Earth | journal= Meteoritics & Planetary Science | volume=35 | pages=1309–1320 | issn= 1086-9379 | year=2000|issue = 6 |doi=10.1111/j.1945-5100.2000.tb01518.x |bibcode = 2000M&PS...35.1309M |s2cid = 129817341 }}</ref><ref>{{cite web|last=|first=|date=|title=Rover reveals Mars was once wet enough for life|url=http://www.msnbc.msn.com/id/4202901/|url-status=dead|archive-url=https://web.archive.org/web/20040210011241/http://www.msnbc.msn.com/id/4202901/|archive-date=February 10, 2004|accessdate=28 July 2009|website=|publisher=[[Microsoft]]}}</ref> About 74% of the surface of Earth is covered by liquid or frozen water. Because of this, people sometimes call it the blue planet.{{refn|''Blue Planet'' is a poetic title for the Earth used in [[movie]]s, in [[magazine|cheap paper book]]s, in [[poetry]], and in government reports (such as the [[European Space Agency]]'s [http://www.esa.int/esapub/bulletin/bulletin137/bul137b_drinkwater.pdf Exploring the water cycle of the Blue Planet])}}

Because of its water, Earth is home to millions of [[species]] of [[plant]]s and [[animal]]s which need water to survive.<ref>{{cite journal|url=http://adsabs.harvard.edu/abs/1988Sci...241.1441M|title= How many species are there on Earth.|publisher=Harvard University|bibcode= 1988Sci...241.1441M|accessdate=2009-07-28|last1= May|first1= Robert M.|journal= Science|year= 1988|volume= 241|issue= 4872|pages= 1441–1449|doi= 10.1126/science.241.4872.1441|pmid= 17790039|s2cid= 34992724}}</ref><ref name="purves_et_al2001">{{cite book| last = Purves| first = William Kirkwood| title = Life, the science of biology| year = 2001| publisher = Macmillan| isbn = 978-0-7167-3873-2| page = 455 }}</ref> The things that live on Earth have changed its surface greatly. For example, early [[cyanobacteria]] changed the [[Atmosphere of Earth#History of Earth's atmosphere|air]] and gave it [[oxygen]]. The living part of Earth's surface is called the "[[biosphere]]".<ref>{{cite web|url=http://www.space.com/searchforlife/life_origins_001205.html|title=Origins of life on Earth|accessdate=2009-07-28|publisher=Space.com|archive-date=2009-07-28|archive-url=https://web.archive.org/web/20090728104629/http://www.space.com/searchforlife/life_origins_001205.html|url-status=dead}}</ref>

==Orbit and turning==

[[File:AxialTiltObliquity.png|thumb|350px|Earth turns at an angle (an "[[axial tilt]]") in relation to its path around the Sun]]

Earth is one of the eight [[planet]]s in the Solar System. There are also thousands of small bodies which move around the Sun. The Solar System is moving through the [[Orion Arm]] of the [[Milky Way]] [[galaxy]], and will be for about the next 10,000 years.<ref>{{cite web|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/030827a.html|title=Earth's location in the Milky Way|accessdate=2009-08-06|publisher=NASA}}</ref><ref>[https://www.forbes.com/sites/startswithabang/2016/04/01/how-fast-does-earth-move-through-the-universe/#42d2c37e4d5c Forbes: How fast does the Earth move through the universe?]</ref>

Earth is about {{convert|150,000,000|km|mi|abbr=off|disp=or}} away from the Sun (this distance is called an "[[Astronomical Unit]]"). It moves on its [[orbit]] at an [[average]] speed of about {{convert|30|km/s|mi/s|abbr=on|lk=on}}.<ref>{{cite web|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html|title=NASA- an Earth fact sheet|accessdate=2009-08-06|publisher=NASA}}</ref> Earth turns all the way around about 365{{Frac|4}} times in the time it takes for Earth to go all the way around the Sun.<ref name="IERS">{{cite web | author=Staff | date=2007-08-07 | url=http://hpiers.obspm.fr/eop-pc/models/constants.html | title=Useful Constants | publisher=International Earth Rotation and Reference Systems Service| accessdate=2008-09-23 }}</ref> To make up this extra bit of a day every year, an [[leap day|additional day]] is used every four years. This is named a "[[leap year]]".

The [[Moon]] goes around Earth at an [[average]] distance of {{convert|250,000|mi|km|abbr=off|order=flip|disp=or}}. It is locked to Earth, so that it always has the same half facing Earth; the other half is called the "dark side of the moon". It takes about 27{{Frac|3}} days for the Moon to go all the way around Earth, but because Earth is moving around the Sun at the same time, it takes about 29{{Frac|2}} days for the Moon to go from dark to bright to dark again. This is where the word "[[month]]" came from, even though most months now have 30 or 31 days.<ref>{{Cite web|last=Espenak|first=Fred|title=Eclipses and the Moon's Orbit|url=https://eclipse.gsfc.nasa.gov/SEhelp/moonorbit.html|access-date=2022-08-10|website=|publisher=[[NASA]]}}</ref>

== History of Earth ==

{{Other pages|Historical geology|Age of the Earth|Giant impact hypothesis|Great Oxygenation Event}}

[[Age of the Earth|Earth]] and the other [[planet]]s formed about 4.6 billion years ago.<ref>{{cite journal| last=Dalrymple | first=G. Brent| title=The age of the Earth in the twentieth century: a problem (mostly) solved | journal=Special Publications, Geological Society of London| year=2001 | volume=190| issue=1 | pages=205–221| doi=10.1144/GSL.SP.2001.190.01.14 |bibcode = 2001GSLSP.190..205D | s2cid=130092094}}

</ref> Their origin was quite different from that of the [[Formation and evolution of the Solar System|Sun]]. The Sun was formed almost entirely of [[hydrogen]], while the planets were formed mostly from higher elements. The smaller "rocky" planets are made almost entirely of higher elements. The Sun must have moved through areas where [[Supernova|supernovae]] had previously exploded.<ref>Sun's motion and in general the motion of stars in the [[Milky Way]] is known from [[Gaia (spacecraft)|Gaia]] data release #2.</ref> All the planets have higher elements which are only made in supernovae.<ref>Burbidge, E.M; Burbidge G.R.; Fowler W.A.; Hoyle F. 1957. Synthesis of the elements in stars. Reviews of Modern Physics. '''29''' (4): 547–650.[https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.29.547]</ref><ref>Clayton D. 2003. ''Handbook of isotopes in the cosmos''. Cambridge University Press. ISBN 978-0-521-82381-4</ref><ref> Kasen D; Metzger B; Barnes J; Quataert E; Ramirez-Ruiz, E. 2017. Origin of the heavy elements in binary neutron-star mergers from a gravitational-wave event. ''Nature''. '''551''' (7678): 80–84.</ref> Only the so-called "[[gas giants]]" have much hydrogen and [[helium]].

The Moon may have been formed after a collision between the early Earth and a smaller planet (sometimes called ''[[Theia]]''). Scientists believe that parts of both planets broke off {{ndash}} becoming (by [[gravity]]) the Moon.<ref>{{cite journal|url=http://www.nature.com/nature/journal/v412/n6848/abs/412708a0.html|title=Origin of the Moon in a giant impact near the end of the Earth's formation|year=2001|accessdate=2009-07-28|publisher=Nature.com|doi=10.1038/35089010|last1=Canup|first1=Robin M.|last2=Asphaug|first2=Erik|journal=Nature|volume=412|issue=6848|pages=708–712|pmid=11507633|bibcode=2001Natur.412..708C|s2cid=4413525}}</ref>

Earth's water came from different places. [[Condensation|Condensing]] [[water vapour]], and [[comet]]s and [[asteroid]]s hitting Earth, made the [[ocean]]s. Within a billion years (that is at about 3.6 billion years ago) the first [[life]] [[evolution|evolved]], in the [[Archaean]] [[era]].<ref>{{cite web|url=http://www.spaceref.com/news/viewnews.html?id=258|title=Earth life appeared on land 1.5 billion years earlier than previously thought|accessdate=2009-07-03|publisher=SpaceRef.com}}</ref><ref>Ghosh, Pallab 2017. Earliest evidence of life on Earth 'found'. BBC News Science & Environment. [2]</ref> Some [[bacteria]] developed [[photosynthesis]], which let them make [[food]] from the Sun's [[light]] and [[water]]. This released a lot of [[oxygen]], which was first taken up by [[iron]] in [[solution]]. Eventually, free oxygen got into the [[atmosphere]] or air, making Earth's surface [[wikt:suitable|suitable]] for [[aerobic]] life (see [[Great Oxygenation Event]]). This oxygen also formed the [[ozone]] [[wikt:layer|layer]] which protects life from [[ultraviolet]] [[radiation]] from the Sun. Complex life on the surface of the land did not exist before the ozone layer.

Earth's land and [[climate]] has been very different in the past. About 3 to 3.5 billion years ago almost all land was in one place. This is called a [[continent|supercontinent]]. The earliest known supercontinent was called [[Vaalbara]]. Much later, there was a time (the [[Cryogenian]]) when Earth was almost entirely covered by thick ice sheets ([[glacier]]s).<ref name="snearth">{{cite web|last=|first=|date=August 8, 1999|title=The Snowball Earth|url=http://www.eps.harvard.edu/people/faculty/hoffman/snowball_paper.html|url-status=dead|archiveurl=https://web.archive.org/web/20090910075356/http://www.eps.harvard.edu/people/faculty/hoffman/snowball_paper.html|archivedate=2009-09-10|accessdate=2009-07-28|work=Paul F. Hoffman and Daniel P. Schrag|publisher=Harvard University}}</ref> This is discussed as the [[Snowball Earth]] [[theory]].<ref name=snearth />

[[File:Terrestrial planet size comparisons.jpg|thumb|right|Size of Earth compared with the other [[terrestrial planet|rocky planets]] in the [[Solar System]]: [[Mercury (planet)|Mercury]], [[Venus]], and [[Mars]]]]

Earth is [[Rock (geology)|rocky]]. It is the largest of the rocky planets moving around the Sun by mass and by size. It is much smaller than the [[gas giant]]s such as [[Jupiter]].

=== Chemical make-up ===

Overall, Earth is made of [[iron]] (32.1[[percent|%]]), [[oxygen]] (30.1[[percent|%]]), [[silicon]] (15.1[[percent|%]]), [[magnesium]] (13.9[[percent|%]]), [[sulfur]] (2.9[[percent|%]]), [[nickel]] (1.8[[percent|%]]), [[calcium]] (1.5[[percent|%]]), and [[aluminium]] (1.4[[percent|%]]). The 1.2[[percent|%]] left over is made of many different kinds of other chemicals. Some rare metals (not just [[gold]] and [[platinum]]) are very valuable. [[Rare earth element|Rare Earth]] metals are used in all types of  electronic phones and computers.

The structure of Earth changes from the inside to the outside. The [[Planetary core|center of earth]] ([[Earth's core]]) is mostly iron (88.8%), nickel (5.8%), sulfur (4.5%), and less than 1% other things.<ref>Morgan J.W. & Anders E. 1980. Chemical composition of Earth, Venus, and Mercury. ''Proceedings of the National Academy of Science'' '''77''' (12): 6973–6977. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC350422/?tool=pmcentrez Chemical composition of Earth, Venus, and Mercury] Full free text</ref> The [[Earth's crust]]  is largely [[oxygen]] (47[[percent|%]]). Oxygen is normally a gas but it can [[oxide|join]] with other [[chemicals]] to make [[chemical compound|compounds]] like [[water]] and rocks. 99.22[[percent|%]] of rocks have [[oxygen]] in them. The most common [[oxygen]]-having rocks are [[silica]] (made with [[silicon]]), [[alumina]] (made with [[aluminum|aluminium]]), [[rust]] (made with [[iron]]), [[lime (chemical)|lime]] (made with [[calcium]]), [[magnesia]] (made with [[magnesium]]), [[potash]] (made with [[potassium]]), and [[sodium]] oxide, and there are others as well.<ref>Chisholm, Hugh (editor). 1911. "Petrology" in the ''Encyclopædia Britannica'', 11th edition. Cambridge University Press.</ref>

*The Earth is the [[density|densest]] of all the planets.<ref>Planetary Fact Sheet - Ratio to Earth Values</ref> It has a lot of heavy metals in it.<ref>Williams, David R. (16 March 2017). "Earth Fact Sheet". NASA/Goddard Space Flight Center. Retrieved 26 July 2018. [https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html]</ref>

=== Shape ===

[[Geoid|Earth's shape]] is a [[spheroid]]: not quite a [[sphere]] because it is slightly [[oblate|squashed]] on the top and bottom. The shape is called an [[oblate spheroid]]. As Earth spins around itself, [[centrifugal force]] forces the [[equator]] out a little and pulls the [[geographical pole|poles]] in a little. The equator, around the middle of Earth's surface, is about {{convert|40,075|km|mi|sp=us|disp=or|sigfig=4}} long.<ref>Measuring the Earth is part of [[geodesy]]</ref> The reason the Earth is roughly a [[sphere]] (and so are all planets and stars) is [[gravity]].<ref>Tipler, Paul A. 1999. ''Physics for scientists and engineers''. 4th ed, New York: W.H. Freeman/Worth Publishers. pp. 336–337. ISBN 9781572594913</ref> Meteorites, on the other hand may be any shape because, in their case, the force of gravity is too weak to change their shape.

The highest mountain above [[sea level]]&mdash;the well-known [[Mount Everest]] (which is {{convert|8848|m|abbr=off|disp=or}} [[elevation|above sea level]])&mdash;is ''not'' actually the one that is the farthest away from the center of the Earth. Instead, the sleeping [[volcano]] [[Mount Chimborazo]] in [[Ecuador]] is; it is only {{convert|

6263|m|abbr=off|disp=or}} [[elevation|above sea level]] but it is almost at the [[equator]]. Because of this, Mount Chimborazo is {{convert|6,384|km|abbr=off|disp=or}} from the center of the Earth, while [[Mount Everest]] is {{convert|2|km|abbr=off|disp=or}} closer to it.<ref>{{cite web|url=http://www.profsurv.com/archive.php?issue=42&article=589|title=Did Edmund Hillary climb the wrong mountain?|work = Professional Surveyor Magazine | volume=20 |issue=5 |first = Joseph H. |last = Senne| date = May 2000|accessdate = 2008-10-24}}</ref><ref name="lancet365_9462_831">{{cite journal | last=Sharp | first=David | title=Chimborazo and the old kilogram | journal=The Lancet | date=2005-03-05 | volume=365 | issue=9462 | pages=831–832 | doi=10.1016/S0140-6736(05)71021-7 | pmid=15752514 | s2cid=41080944 }}</ref><ref name="tall_tales">{{cite web | url=http://www.abc.net.au/science/k2/moments/s1086384.htm | title=Tall tales about highest peaks | date=16 April 2004 | publisher=Australian Broadcasting Corporation | accessdate=2008-12-29}}</ref> Similarly, the lowest point below sea level that we are conscious of is the [[Challenger Deep]] in the [[Mariana Trench]] in the [[Pacific Ocean]]. It is about {{convert|10971|m|abbr=off|disp=or}} [[depth|below sea level]],<ref name="kaiko7000">{{cite web|title=7,000&nbsp;m Class Remotely Operated Vehicle ''KAIKO 7000''|url=http://www.jamstec.go.jp/e/about/equipment/ships/kaiko7000.html|publisher=Japan Agency for Marine-Earth Science and Technology (JAMSTEC)|accessdate=2008-06-07}}</ref> but, again, there are probably places at the bottom of the [[Arctic Ocean]] that are nearer to the center of the Earth.

=== Earth’s core ===

[[File:Earth-crust-cutaway-english.svg|thumb|right|220px|A picture of the inside of the Earth, showing the different levels. In fact, the air and the outside levels are much thinner than shown here]]

The [[Kola superdeep borehole|deepest hole ever dug]] is only about {{convert|12.3|km|mi|disp=or|sp=us|sigfig=2}}. We know something about the inside of the Earth, though, because we can learn things from [[earthquake]]s and the times when [[volcano]]es [[Volcanic eruption|erupt]]. We are able to see how quickly the [[shock wave]]s move through Earth in different places.

The inside of Earth is very different from the outside. Almost all of Earth's liquid water is in the [[ocean|sea]]s or close to the surface. The surface also has a lot of [[oxygen]], which comes from plants. Small and simple kinds of life can live far under the surface, but animals and plants only live on the surface or in the seas. The rocks on the surface of Earth ([[Earth's crust]]) are well known. They are thicker where there is land, between {{convert|30|to|50|km|mi|disp=or|sp=us|abbr=on|sigfig=2}} thick. Under the [[ocean|sea]]s they are sometimes only {{convert|6|km|mi|disp=or|sp=us|abbr=on|sigfig=2}} thick.<ref>{{cite web|author=Toshiro Tanimoto|date=|title=Crustal Surface of the Earth|url=http://www.agu.org/reference/gephys/15_tanimoto.pdf|url-status=dead|archive-url=https://web.archive.org/web/20030410215144/http://www.agu.org/reference/gephys/15_tanimoto.pdf|archive-date=April 10, 2003|accessdate=2009-08-02|website=|publisher=American Geophysical Union}}</ref> There are three groups of rocks that make up most of the Earth's crust. Some rock is made when the hot liquid rock comes from inside the earth ([[igneous rock]]s); another type of rock is made when [[sediment]] is laid down, usually under the sea ([[sedimentary rock]]s); and a third kind of rock is made when the other two are changed by very high [[temperature]] or [[pressure]] ([[metamorphic rock]]s). A very few rocks also fall out of the sky ([[meteorite]]s).

Below the crust is hot and almost-[[liquid]] rock which is always moving around (the [[Earth's mantle]]). Then, there is a thin liquid layer of heated rock (the [[outer core]]). This is very hot: {{convert|7000|°C|°F K|disp=or|sigfig=2}}.<ref>{{cite web|url=http://chianti.geol.ucl.ac.uk/~dario/pubblicazioni/PTRSA2002.pdf|title=The ab initio simulation of the Earth's core|date=2002-04-25|accessdate=2009-08-02|publisher=The Royal Society|author=D. Alfé}}</ref> The middle of the inside of the Earth would be liquid as well but all the pressure of the rock above it makes it a  solid. This solid middle part (the [[inner core]]) is almost all [[iron]]. It is what makes the Earth [[magnetic field|magnetic]].

=== Pieces of the crust form plates ===

[[File:Plates tect2 en.svg|thumb|right|A [[map|picture]] showing the Earth's largest and most important plates.]]

{{main|Plate tectonics}}

The [[Earth's crust]] is solid but made of [[plate tectonics|parts]] which move very slowly.<ref name="jour">{{cite journal| last=Tackley | first=Paul J.| title=Mantle convection and plate tectonics: towards an integrated physical and chemical theory| journal=Science | date=2000-06-16| volume=288 | issue=5473 | pages=2002–2007| doi=10.1126/science.288.5473.2002| pmid=10856206 | bibcode=2000Sci...288.2002T}}</ref> The thin skin of hard rock on the outside of the Earth rests on hot liquid material below it in the deeper [[mantle (geology)|mantle]].<ref name="TecPlates">{{cite web|last=|first=|date=|title=The Crust|url=http://volcano.oregonstate.edu/education/vwlessons/lessons/Earths_layers/Earths_layers4.html|url-status=dead|archive-url=https://web.archive.org/web/20091213011245/http://volcano.oregonstate.edu/education/vwlessons/lessons/Earths_layers/Earths_layers4.html|archive-date=December 13, 2009|accessdate=2009-07-03|website=|publisher=Oregon State University}}</ref> This liquid material moves because it gets heat from the hot center of the Earth. The slow movement of the plates is what causes [[earthquake]]s, [[volcano]]es and large groups of mountains on the Earth.

There are three ways plates can come together. Two plates can move towards each other ("convergent" plate edges). This can form [[island]]s, [[volcanoes]], and high [[mountain range]]s (such as the [[Andes]] and [[Himalayas]]).<ref name="book1">{{cite book| last1 = Seyfert| first1 = Carl K.| last2 = Seyfert| first2 = Carl| last3 = Seyfert| first3 = Claus| title = The encyclopedia of structural geology and plate tectonics| url = https://archive.org/details/encyclopediaofst0000unse| year = 1987| publisher = Springer| isbn = 978-0-442-28125-0 }}</ref> Two plates can move away from each other ("divergent" plate edges). This gives the [[magma|warm liquid rock inside the earth]] a place to come out. This makes [[mid-ocean ridge|special mountain range]]s below the sea or large low lands like [[Africa]]'s [[Great Rift Valley]].<ref name="'platetectonics.com'">{{cite web |title=Plate Tectonics: plate boundaries |url=http://www.platetectonics.com/book/page_5.asp |publisher=platetectonics.com |accessdate=12 June 2010 |archive-date=16 June 2010 |archive-url=https://web.archive.org/web/20100616062513/http://www.platetectonics.com/book/page_5.asp |url-status=dead }}</ref><ref name="'usgs.understanding.com'">{{cite web |title=Understanding plate motions |url= http://pubs.usgs.gov/gip/dynamic/understanding.html|publisher=USGS|accessdate=12 June 2010}}</ref> Plates are able to move beside each other as well ("transform" plate edges, such as the [[San Andreas Fault]]). This makes their edges crush against each other and makes many [[earthquakes|shocks as they move]].<ref name="book2">{{cite book|title=Plate tectonics: an insider's history of the modern theory of the Earth|isbn=0813341329|last=Oreskes|first=Naomi|publisher=Westview Press|year=2003}}</ref>

The outside of the Earth is not even. There are high places called [[mountain]]s, and high flat places called [[plateau]]s. There are low places called [[valley]]s and [[canyon]]s. For the most part, moving [[wind|air]] and [[rain|water from the sky]] and [[tide|sea]]s [[erosion|damages rocks in high places and breaks them into small pieces]]. The air and water then move these pieces to lower places. Because of this, the Earth would have been very flat a long time before now. The fundamental cause of the differences in the Earth's surface is [[plate tectonics]]. The shape of the entire planet itself is not even a ball. Because of its velocity, Earth has a slight bulge at the [[Equator]]. Other than that, Earth is shaped more like a pear than an actual sphere.

All places on Earth are made of, or are on top of, rocks. The outside of the Earth is usually not uncovered rock. Over 70[[percent|%]] of the Earth is covered by [[ocean|sea]]s full of [[salt]]y water.<ref name="Physical-Hydro">{{cite web|url=http://www.physicalgeography.net/fundamentals/8a.html|title=Chapter 8: Introduction to the Hydrosphere|accessdate=2009-08-06|publisher=Physical Geography}}</ref> This salty water makes up about 97{{Frac|2}}[[percent|%]] of all Earth's water. The [[fresh water]] people can drink is mostly [[ice]]. Only a very small amount is in [[river]]s and under the Earth for people to drink and use.<ref>{{cite web|last=|first=|date=|title=World water resources and their uses|url=http://webworld.unesco.org/water/ihp/db/shiklomanov/|url-status=dead|archive-url=https://web.archive.org/web/20010720061344/http://webworld.unesco.org/water/ihp/db/shiklomanov/|archive-date=July 20, 2001|accessdate=2009-08-06|website=|publisher=UNESCO}}</ref> The air above the Earth stops the water from going away into [[outer space]]. Also, much of the land on Earth is covered with plants, or with what is left from earlier living things. Places with very little rain are dry wastes called [[desert]]s. Deserts usually have few living things, but life is able to grow very quickly when these wastes have rainfall. Places with large amounts of rain may be [[rain forest|large woods]]. Lately, people have changed the [[environment]] of the Earth a great deal.

=== Air ===

All around the Earth is the of air (the [[atmosphere]]). The mass of the Earth holds the [[gas]]ses in the air down and does not let them go into outer space. The air is mostly made of [[nitrogen]] (about 78[[percent|%]]) and [[oxygen]] (about 21[[percent|%]]) and there are a few other gasses as well.<ref>{{cite web|url=http://www.nasa.gov/audience/forstudents/9-12/features/912_liftoff_atm.html|title=NASA - Earth's atmosphere|accessdate=2009-08-06|publisher=NASA}}</ref> Most living things need the air (or parts of the air gripped in the water) to breathe and live. They use the gasses&mdash;especially [[oxygen]] and [[carbon dioxide]]&mdash;to make and use [[sugar]] and to give themselves power.

The air animals and plants use to live is only the first level of the air around the Earth (the [[troposphere]]). The day to day changes in this level of air are called [[weather]]; the larger differences between distant places and from year to year are called the [[climate]]. [[Rain]] and [[storm]]s come about because this part of the air gets colder as it goes up. [[convection|Cold air becomes thicker and falls, and warm air becomes thinner and goes up]].<ref name="NASA">{{cite web|last=|first=|date=|title=What causes weather?|url=http://www.nasa.gov/worldbook/weather_worldbook.html|url-status=dead|archive-url=https://web.archive.org/web/20050501070321/http://www.nasa.gov/worldbook/weather_worldbook.html|archive-date=May 1, 2005|accessdate=2009-08-06|website=|publisher=NASA}}</ref> The turning Earth moves the air as well and air moves north and south because the middle of the Earth generally gets more power from the Sun and is warmer than the north and south points. Air over warm water [[evaporation|evaporates]] but, because cold air is not able to take in as much water, it starts to make [[cloud]]s and [[rain]] as it gets colder. The way water moves around in a circle like this is called the [[water cycle]].<ref name= NASA />

Above this first level, there are four other levels. The air gets colder as it goes up in the first level; in the second level (the [[stratosphere]]), the air gets warmer as it goes up. This level has a special kind of [[oxygen]] called [[ozone]]. The [[ozone]] in this air keeps living things safe from [[ultraviolet radiation|damaging rays from the Sun]]. The power from these rays is what makes this level warmer and warmer. The middle level (the [[mesosphere]]) gets colder and colder with height; the fourth level (the [[thermosphere]]) gets warmer and warmer; and the last level (the [[exosphere]]) is almost outer space and has very little air at all. It reaches about half the way to the Moon. The three outer levels have a lot of [[electricity|electric power]] moving through them; this is called the [[ionosphere]] and is important for [[radio]] and other electric waves in the air. It is also where the [[Northern Lights]] are.

Even though air seems very light, the weight of all of the air above the outside of the Earth ([[air pressure]]) is important. Generally, from [[sea level]] to the top of [[exosphere|the outer level of the air]], a space of air one [[square centimeter|cm²]] across has a mass of about 1.03 [[kilogram|kg]] and a space of air one [[square inch|sq in]] across has a weight of about 14.7 [[Pound (mass)|lb]]. Because of the air, small meteorites generally burn up long before they get to the earth.

The air also keeps the Earth warm, specially the half turned away from the Sun. Some gasses &ndash; especially [[methane]] and [[carbon dioxide]] &ndash; [[greenhouse effect|work like a blanket to keep things warm]].<ref>{{cite web|url=http://www.physicalgeography.net/fundamentals/7h.html|title=Fundamentals of physical geography - the greenhouse effect|accessdate=2009-08-06|publisher=Physical Geography}}</ref> [[#History of Earth|In the past]], the Earth has been much warmer and much colder than it is now. Since people have grown used to the heat we have now, though, we do not want the Earth to be too much warmer or colder. Most of the ways people create [[electricity|electric power]] use burning kinds of [[carbon]]&mdash;especially [[coal]], [[oil]], and [[natural gas]]. Burning these creates new [[carbon dioxide]] and can cause more warming. A [[climate change|large discussion]] is going on now about what people should do about [[global warming|the Earth's latest warming]], which has gone on for about 150 years. So far, this warming has been acceptable: plants have grown better. The weather has been better than [[Little Ice Age|when it was colder]]. Bad things will possibly come about if the warming goes on.

== People                                                                                                                                                                      ==

About eight [[billion]] people live on Earth. They live in about 200 different lands called [[countries]]. Some, for example, [[Russia]], are large with many large cities. Others, for example, [[Vatican City]], are small. The seven countries with the most people are [[China]], [[India]], the [[United States]], [[Indonesia]],  [[Pakistan]], [[Brazil]] and [[Nigeria]]. About 90% of people live in the [[northern hemisphere]] of the world, which has most of the land. Human beings originally came from [[Africa]]. Now, 70% of all people do not live in Africa but in [[Europe]] and [[Asia]].<ref>Diamond, Jared. 1997. ''[[Guns, Germs, and Steel]]: the fate of human societies''. New York: Norton.</ref>

[[File:Population_density.png|link=https://en.wikipedia.org/wiki/File:Population_density.png|alt=|thumb|center|350px|The distribution of human [[world population]] in 2018]]

People change the Earth in many ways. They have been able to grow plants for food and clothes for about ten thousand years. When there was enough food, they were able to build towns and cities. Near these places, men and women were able to change rivers, [[irrigation|bring water to farms]], and stop [[flood]]s (rising water) from coming over their land. People found useful animals and [[domestication|bred]] them so they were easier to keep.

== Gallery ==

{{LifeOnEarth}}{{LocationOfEarth}}

== Related pages ==

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{{reflist|2}}

{{Commons|Earth}}

{{wiktionary|Earth|earth}}

* {{cite web | url = http://www.solarviews.com/eng/earth.htm | title = Solar Views | publisher = Calvin J. Hamilton }}

* {{cite web | url = http://www.earth.nasa.gov/science/questions.html | title = Earth – Science questions | publisher = [[NASA]]}}

* {{cite web | url = https://nightsky.jpl.nasa.gov/docs/HowFast.pdf | title = Earth – Speed through space – about 1 million miles an hour<!---between 0.8 - 1.9 M mph---> | publisher = [[NASA]]}}  ("[[w:Wikipedia:Reference desk/Archives/Science/2019 July 20#How fast are we moving through space?|WP discussion]]")

* {{cite web | url = https://technological-sci.blogspot.com/2020/04/10-unique-feature-of-earth.html| title = 3 unique feature of earth | publisher = Technological-Sci }}