Editing Comet (section)

=== Comets and impact on life ===

Many comets and asteroids collided with Earth in its early stages. Many scientists think that comets bombarding the young Earth about 4&nbsp;billion years ago brought the [[Origin of water on Earth|vast quantities of water]] that now fill Earth's oceans, or at least a significant portion of it. Others have cast doubt on this idea.<ref>{{cite web |last=Muir |first=Hazel |title=Earth's water brewed at home, not in space |url=https://www.newscientist.com/article/dn12693 |work=New Scientist |date=25 September 2007 |access-date=30 August 2013}}</ref> The detection of organic molecules, including [[polycyclic aromatic hydrocarbon]]s,<ref name="NASA-20150210">{{cite web |last=Clavin |first=Whitney |title=Why Comets Are Like Deep Fried Ice Cream |url=http://www.jpl.nasa.gov/news/news.php?feature=4480 |date=10 February 2015 |publisher=[[NASA]] |access-date=10 February 2015}}</ref> in significant quantities in comets has led to speculation that comets or [[meteorite]]s may have brought the precursors of life—or even life itself—to Earth.<ref>{{cite book |url=https://books.google.com/books?id=Dfn0VoICrBYC&pg=PA315 |page=315 |title=Comets |isbn=978-1-4020-3495-4 |last=Fernández |first=Julio A. |date=2006|publisher=Springer }}</ref> In 2013 it was suggested that impacts between rocky and icy surfaces, such as comets, had the potential to create the [[amino acid]]s that make up [[protein]]s through [[shock synthesis]].<ref>{{cite journal |doi=10.1038/ngeo1930 |title=Shock synthesis of amino acids from impacting cometary and icy planet surface analogues |date=2013 |last1=Martins |first1=Zita |last2=Price |first2=Mark C. |last3=Goldman |first3=Nir |last4=Sephton |first4=Mark A. |last5=Burchell |first5=Mark J. |display-authors=1 |journal=Nature Geoscience |bibcode=2013NatGe...6.1045M |volume=6 |issue=12 |pages=1045–1049}}</ref> The speed at which the comets entered the atmosphere, combined with the magnitude of energy created after initial contact, allowed smaller molecules to condense into the larger macro-molecules that served as the foundation for life.<ref>{{Cite web|url=https://www.astrobio.net/also-in-news/did-comet-impacts-jump-start-life-on-earth/|title=Did comet impacts jump-start life on Earth?|date=2019-10-18|website=Astrobiology Magazine|language=en-US|access-date=2019-12-01 |archive-url=https://web.archive.org/web/20210308143059/https://www.astrobio.net/also-in-news/did-comet-impacts-jump-start-life-on-earth/ |archive-date=2021-03-08 |url-status=usurped}}</ref> In 2015, scientists found significant amounts of molecular oxygen in the outgassings of comet 67P, suggesting that the molecule may occur more often than had been thought, and thus less an indicator of life as has been supposed.<ref>Oregonian (29 Oct 2015), "Comet's oxygen shakes theories on solar system", p. A5</ref>

It is suspected that comet impacts have, over long timescales, delivered significant quantities of water to Earth's [[Moon]], some of which may have survived as [[lunar ice]].<ref>{{cite web |url=http://lunarscience.nasa.gov/articles/water-discovered-in-apollo-moon-rocks-likely-came-from-comets/ |title=Water Discovered in Apollo Moon Rocks Likely Came from Comets |access-date=7 September 2013 |publisher=NASA}}</ref> Comet and [[meteoroid]] impacts are thought to be responsible for the existence of [[tektite]]s and [[australite]]s.<ref>{{cite web |url=http://museumvictoria.com.au/discoverycentre/infosheets/australites/ |archive-url=https://web.archive.org/web/20080726071448/http://museumvictoria.com.au/DiscoveryCentre/Infosheets/Australites/ |url-status=dead |archive-date=26 July 2008 |title=Australites |publisher=Museum Victoria |access-date=7 September 2013}}</ref>