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Natural shielding against space weather and solar wind, such as the magnetosphere depicted in this artistic rendition, is required for planets to sustain life for prolonged periods.

A Habitable Zone for Complex Life (HZCL) is a range of distances from a star suitable for complex aerobic life. Different types of limitations preventing complex life give rise to different zones.[1] Conventional habitable zones are based on compatibility with water.[2] Most zones start at a distance from the host star and then end at a distance farther from the star. A planet or exoplanet (a planet outside the Solar System) would need to orbit inside the boundaries of this zone. With multiple zonal constraints, the zones would need to overlap for the planet to support complex life. The requirements for bacterial life produce much larger zones than those for complex life, which requires a very narrow zone.[3][4][5]

Exoplanets

Main articles: Exoplanets and Earth analog

The first confirmed exoplanets was discovered in 1992, several planets orbiting the pulsar PSR B1257+12.[6] Since then the list of exoplanets has grown to the thousands.[7] Most exoplanets are hot Jupiter planets, that orbit very close the star.[8] Many exoplanets are super-Earths, that could be a gas dwarf or large rocky planet, like Kepler-442b at a mass 2.36 times Earths.[9]

Star

Main articles: Star and Solar twin

Unstable stars are young and old stars, or very large or small stars. Unstable stars have changing solar luminosity that changes the size of the life habitable zones. Unstable stars also produce extreme solar flares and coronal mass ejections. Solar flares and coronal mass ejections can strip away a planet's atmosphere that is not replaceable. Thus life habitable zones require and very stable star like the Sun, at ±0.1% solar luminosity change.[10][11] Finding a stable star, like the Sun, is the search for a solar twin, with solar analogs that have been found.[12] Stars with an age of 4.6 billion years are at the most stable state. Proper star metallicity, size, mass, age, color, and temperature are also very important to having low luminosity variations.[13][14][15] The Sun is unique as it is metal rich for its age and type, a G2V star. The Sun is currently in its most stable stage and has the correct metallicity to make it very stable.[16] Dwarf stars (red dwarf/orange dwarf/brown dwarf/subdwarf) are not only unstabe, but also emit low energy, so habitable zone is very close to the star and the planet is tidally locked. Planet very close also puts it out of almost all the Life habitable zones.[17] Giant stars (subgiant/giant star/red giant/red supergiant) are unstable and emit high energy, so habitable zone is very far from star. Planet very far out also puts it out of almost all the Life habitable zones, in a place were there are no rocky planets.[18]

Named habitable zones

Main article: Habitable zone

A conventional habitable zone is defined by liquid water.

Named habitable zones for complex life

Over time and with more research, astronomers, cosmologists and astrobiologist have discovered more parameters needed for life. Each parameter could have a corresponding zone. Some of the named zones include:[25][26]

Carbon Dioxide habitable and Carbon Monoxide habitable zone

Other orbital-distance related factors

Some factors that depend on planetary distance and may limit complex aerobic life have not been given zone names. These include:

Life

Main articles: Life and Carbon-based life

Life on Earth is carbon-based. However, some theories suggest that life could be based on other elements in the periodic table.[109] Other elements proposed have been silicon, boron, arsenic, ammonia, methane and others. As more research as been done on life on Earth, it has been found that only carbon's organic molecules have the complexity and stability to form life.[110][111][112] Carbon properties allows for complex chemical bonding that produces covalent bonds needed for organic chemistry. Carbon molecules are lightweight and relatively small in size. Carbon's ability to bond to oxygen, hydrogen, nitrogen, phosphorus, and sulfur (called CHNOPS) is key to life.[113] [114][115]

Gallery

See also

References

  1. ^ "Not All Habitable Zones Are Created Equal". www.spacedaily.com.
  2. ^ a b c d Schwieterman, Edward W.; Reinhard, Christopher T.; Olson, Stephanie L.; Harman, Chester E.; Lyons, Timothy W. (June 10, 2019). "A Limited Habitable Zone for Complex Life". The Astrophysical Journal. 878 (1): 19. arXiv:1902.04720. Bibcode:2019ApJ...878...19S. doi:10.3847/1538-4357/ab1d52.
  3. ^ a b "New Discovery Shows 'Habitable Zone for Complex Life' is Much More Narrow than Original Estimates – NASA". June 10, 2019.
  4. ^ a b Williams, Matt; Today, Universe. "Complex life might require a very narrow habitable zone". phys.org.
  5. ^ How do you form a habitable planet?, Georgia State University Research
  6. ^ Wolszczan, A.; Frail, D. A. (1992). "A planetary system around the millisecond pulsar PSR1257 + 12". Nature. 355 (6356): 145–147. Bibcode:1992Natur.355..145W. doi:10.1038/355145a0. S2CID 4260368.
  7. ^ "Exoplanet and Candidate Statitics". exoplanetarchive.ipac.caltech.edu.
  8. ^ "Orbital Evolution of planets in Extra-solar systems". users.auth.gr.
  9. ^ Valencia, V.; Sasselov, D. D.; O'Connell, R. J. (2007). "Radius and structure models of the first super-earth planet". The Astrophysical Journal. 656 (1): 545–551. arXiv:astro-ph/0610122. Bibcode:2007ApJ...656..545V. doi:10.1086/509800. S2CID 17656317.
  10. ^ a b c Green, James; Boardsen, Scott; Dong, Chuanfei (February 20, 2021). "Magnetospheres of Terrestrial Exoplanets and Exomoons: Implications for Habitability and Detection". The Astrophysical Journal Letters. 907 (2): L45. arXiv:2012.11694. Bibcode:2021ApJ...907L..45G. doi:10.3847/2041-8213/abd93a.
  11. ^ a b Brasch, Klaus R. (July 7, 2023). "Is Earth the only Goldilocks planet? | Astronomy.com".
  12. ^ "Solar Variability and Terrestrial Climate – NASA Science". science.nasa.gov.
  13. ^ "Stellar Luminosity Calculator". astro.unl.edu.
  14. ^ The Effects of Solar Variability on Earth's Climate: A Workshop Report. National Academies Press. November 12, 2012. doi:10.17226/13519. ISBN 978-0-309-26564-5.
  15. ^ "Most of Earth's twins aren't identical, or even close! | ScienceBlogs". scienceblogs.com.
  16. ^ a b "NASA Astrobiology". astrobiology.nasa.gov.
  17. ^ Barnes, Rory, ed. (2010). Formation and Evolution of Exoplanets. John Wiley & Sons. p. 248. ISBN 978-3527408962. Archived from the original on 2023-08-06. Retrieved 2016-08-16.
  18. ^ Voisey, Jon (February 23, 2011). "Plausibility Check - Habitable Planets around Red Giants".
  19. ^ "Big Idea 2.1 – NASA Science". science.nasa.gov.
  20. ^ "What Is the Habitable Zone?". Exoplanet Exploration: Planets Beyond our Solar System.
  21. ^ "Planets in the habitable zone". www.esa.int.
  22. ^ a b c "Which habitable zone planets are the best candidates for detecting life? | astrobites".
  23. ^ "Second Earth-sized World Found in System's Habitable Zone". Exoplanet Exploration: Planets Beyond our Solar System.
  24. ^ "The Habitable Zone | Astronomy 801: Planets, Stars, Galaxies, and the Universe". www.e-education.psu.edu.
  25. ^ Taylor, Stuart Ross (29 July 2004). "Why can't planets be like stars?". Nature. 430 (6999): 509. Bibcode:2004Natur.430..509T. doi:10.1038/430509a. PMID 15282586. S2CID 12316875.
  26. ^ Stern, Alan. "Ten Things I Wish We Really Knew In Planetary Science". Retrieved 2009-05-22.
  27. ^ Cowing, Keith (March 30, 2023). "The Ultraviolet Habitable Zone Of Exoplanets". Astrobiology.
  28. ^ Spinelli, Riccardo; Borsa, Francesco; Ghirlanda, Giancarlo; Ghisellini, Gabriele; Haardt, Francesco (April 13, 2023). "The ultraviolet habitable zone of exoplanets". Monthly Notices of the Royal Astronomical Society. 522 (1): 1411–1418. arXiv:2303.16229. doi:10.1093/mnras/stad928.
  29. ^ "Habitable zones :: Vera Dobos". veradobos.webnode.page.
  30. ^ Hall, C.; Stancil, P. C.; Terry, J. P.; Ellison, C. K. (May 1, 2023). "A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone". The Astrophysical Journal Letters. 948 (2): L26. arXiv:2301.13836. Bibcode:2023ApJ...948L..26H. doi:10.3847/2041-8213/acccfb.
  31. ^ Blog, The Physics arXiv (February 24, 2023). "A new place to look for alien life: The photosynthetic habitable zone".
  32. ^ Hall, C.; Stancil, P. C.; Terry, J. P.; Ellison, C. K. (May 1, 2023). "A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone". The Astrophysical Journal Letters. 948 (2): L26. arXiv:2301.13836. Bibcode:2023ApJ...948L..26H. doi:10.3847/2041-8213/acccfb.
  33. ^ N.H. Sleep “Tectonics and the photosynthetic habitable zone” American Geophysical Union, Fall 2009, abstract #B11E-03
  34. ^ Association, American Lung. "Ozone". www.lung.org.
  35. ^ Proedrou, Elisavet; Hocke, Klemens (June 1, 2016). "Characterising the three-dimensional ozone distribution of a tidally locked Earth-like planet". Earth, Planets and Space. 68 (1): 96. Bibcode:2016EP&S...68...96P. doi:10.1186/s40623-016-0461-x.
  36. ^ "Photochemical Smog - an overview | ScienceDirect Topics". www.sciencedirect.com.
  37. ^ Yang, Jun; Boué, Gwenaël; Fabrycky, Daniel C.; Abbot, Dorian S. (May 1, 2014). "Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate". The Astrophysical Journal. 787 (1): L2. arXiv:1404.4992. Bibcode:2014ApJ...787L...2Y. doi:10.1088/2041-8205/787/1/L2 – via NASA ADS.
  38. ^ "Rotation of planets influences habitability". phys.org.
  39. ^ Jansen, T. (March 19, 2021). "Effects of Rotation Rate on the Habitability of Earth-like Planets using NASA's ROCKE-3D GCM". Bulletin of the AAS. 53 (3): 0603. Bibcode:2021BAAS...53c0603J – via baas.aas.org.
  40. ^ The Moon's Role in the Habitability of the Earth, Georgia State University Research
  41. ^ Seasons, Georgia State University Research
  42. ^ Ecliptic Plane, Georgia State University Research
  43. ^ Axis Tilt is Critical for Life, Georgia State, astr.gsu.edu
  44. ^ Starr, Michelle (July 8, 2021). "This One Planetary Feature May Be Crucial For The Rise of Complex Life in The Universe". ScienceAlert.
  45. ^ Conference, Goldschmidt. "Goldilocks planets 'with a tilt' may develop more complex life". phys.org.
  46. ^ Jenkins, Gregory S. (March 27, 2000). "Global climate model high-obliquity solutions to the ancient climate puzzles of the Faint-Young Sun Paradox and low-altitude Proterozoic glaciation". Journal of Geophysical Research: Atmospheres. 105 (D6): 7357–7370. Bibcode:2000JGR...105.7357J. doi:10.1029/1999JD901125 – via CrossRef.
  47. ^ Becker, Juliette; Seligman, Darryl Z.; Adams, Fred C.; Styczinski, Marshall J. (March 1, 2023). "The Influence of Tidal Heating on the Habitability of Planets Orbiting White Dwarfs". The Astrophysical Journal Letters. 945 (2): L24. arXiv:2303.02217. Bibcode:2023ApJ...945L..24B. doi:10.3847/2041-8213/acbe44.
  48. ^ Hasler, Caroline (February 17, 2022). "Tidally Locked and Loaded with Questions". Eos.
  49. ^ "New conditions for life on other planets: Tidal effects change 'habitable zone' concept". ScienceDaily.
  50. ^ Vladimir S. Airapetian, “Space Weather Affected Habitable Zones around Active Stars,” AASTCS5 Radio Exploration of Planetary Habitability, Proceedings of the Conference, May 7–12, 2017 in Palm Springs, CA, published in the Bulletin of the American Astronomical Society 49, no. 3, id. 101.05
  51. ^ Smith, David S.; Scalo, John M. (September 20, 2009). "Habitable zones exposed: astrosphere collapse frequency as a function of stellar mass". Astrobiology. 9 (7): 673–681. Bibcode:2009AsBio...9..673S. doi:10.1089/ast.2009.0337. PMID 19778278 – via PubMed.
  52. ^ Time History of the Martian Dynamo from Crater Magnetic Field Analysis Journal of Geophysical Research: Planets 118, no. 7 (July 2013), by Robert J. Lillis et al., page 1488–1511
  53. ^ Timing of the Martian Dynamo Nature 408, by G. Schubert, C. T. Russell, and W. B. Moore, December 7, 2000: page 666–667
  54. ^ Langlais, Benoit; Thébault, Erwan; Houliez, Aymeric; Purucker, Michael E.; Lillis, Robert J. (2019). "A New Model of the Crustal Magnetic Field of Mars Using MGS and MAVEN". Journal of Geophysical Research: Planets. 124 (6): 1542–1569. Bibcode:2019JGRE..124.1542L. doi:10.1029/2018JE005854. ISSN 2169-9100. PMC 8793354. PMID 35096494.
  55. ^ "Space Radiation is Risky Business for the Human Body – NASA". September 19, 2017.
  56. ^ Collinson, Glyn A.; Frahm, Rudy A.; Glocer, Alex; Coates, Andrew J.; Grebowsky, Joseph M.; Barabash, Stas; Domagal-Goldman, Shawn D.; Fedorov, Andrei; Futaana, Yoshifumi; Gilbert, Lin K.; Khazanov, George; Nordheim, Tom A.; Mitchell, David; Moore, Thomas E.; Peterson, William K.; Winningham, John D.; Zhang, Tielong L. (June 28, 2016). "The electric wind of Venus: A global and persistent "polar wind"-like ambipolar electric field sufficient for the direct escape of heavy ionospheric ions". Geophysical Research Letters. 43 (12): 5926–5934. Bibcode:2016GeoRL..43.5926C. doi:10.1002/2016GL068327. S2CID 54886960 – via CrossRef.
  57. ^ Collinson, Glyn; Mitchell, David; Glocer, Alex; Grebowsky, Joseph; Peterson, W. K.; Connerney, Jack; Andersson, Laila; Espley, Jared; Mazelle, Christian; Sauvaud, Jean-André; Fedorov, Andrei; Ma, Yingjuan; Bougher, Steven; Lillis, Robert; Ergun, Robert; Jakosky, Bruce (November 16, 2015). "Electric Mars: The first direct measurement of an upper limit for the Martian "polar wind" electric potential". Geophysical Research Letters. 42 (21): 9128–9134. Bibcode:2015GeoRL..42.9128C. doi:10.1002/2015GL065084 – via CrossRef.
  58. ^ "Strong 'electric wind' strips planets of oceans and atmospheres". UCL News. June 20, 2016.
  59. ^ "Eccentric Habitable Zones". Exoplanet Exploration: Planets Beyond our Solar System.
  60. ^ Zubritsky, Elizabeth. "Jupiter's Youthful Travels Redefined Solar System". NASA. Retrieved 4 November 2015.
  61. ^ Beatty, Kelly (16 October 2010). "Our "New, Improved" Solar System". Sky & Telescope. Retrieved 4 November 2015.
  62. ^ Sanders, Ray (23 August 2011). "How Did Jupiter Shape Our Solar System?". Universe Today. Retrieved 4 November 2015.
  63. ^ https://astrobiology.nasa.gov/news/exoplanets-with-complex-life-may-be-very-rare-even-in-their-habitable-zones/ Exoplanets With Complex Life May Be Very Rare, Even in Their “Habitable Zones”, nasa.gov]
  64. ^ Schwieterman, Edward W., et al. "A limited habitable zone for complex life." The Astrophysical Journal 878.1 (2019): 19
  65. ^ Allen, Michael (June 15, 2019). "Toxic gases in habitable zone could hinder emergence of alien life". Physics World.
  66. ^ Liu, Hui; Tian, Yaohua; Xiang, Xiao; Li, Man; Wu, Yao; Cao, Yaying; Juan, Juan; Song, Jing; Wu, Tao; Hu, Yonghua (September 6, 2018). "Association of short-term exposure to ambient carbon monoxide with hospital admissions in China". Scientific Reports. 8 (1): 13336. Bibcode:2018NatSR...813336L. doi:10.1038/s41598-018-31434-1. PMC 6127141. PMID 30190544.
  67. ^ a b "New study dramatically narrows the search for advanced life in the universe | UCR News | UC Riverside". news.ucr.edu.
  68. ^ "Hubble Views Striking Carbon Star in Colorful Cluster – NASA Science". science.nasa.gov.
  69. ^ "Carbon monoxide in large-star disks". Nature. 537 (7619): 140. September 20, 2016. doi:10.1038/537140b. PMID 27604918 – via www.nature.com.
  70. ^ See, V.; Jardine, M.; Vidotto, A. A.; Petit, P.; Marsden, S. C.; Jeffers, S. V.; Nascimento, J. D. do (October 1, 2014). "The effects of stellar winds on the magnetospheres and potential habitability of exoplanets". Astronomy & Astrophysics. 570: A99. arXiv:1409.1237. Bibcode:2014A&A...570A..99S. doi:10.1051/0004-6361/201424323 – via www.aanda.org.
  71. ^ "Planetary Habitability page of the Trieste Astrobiology Group". wwwuser.oats.inaf.it.
  72. ^ Vladilo, Giovanni; Murante, Giuseppe; Silva, Laura; Provenzale, Antonello; Ferri, Gaia; Ragazzini, Gregorio (March 25, 2013). "The Habitable Zone Of Earth-Like Planets With Different Levels Of Atmospheric Pressure". The Astrophysical Journal. 767 (1): 65. arXiv:1302.4566. Bibcode:2013ApJ...767...65V. doi:10.1088/0004-637x/767/1/65.
  73. ^ "Mars & Comets – NASA". mars.nasa.gov.
  74. ^ Nair, C. P. Reghunadhan; Unnikrishnan, Vibhu (April 18, 2020). "Stability of the Liquid Water Phase on Mars: A Thermodynamic Analysis Considering Martian Atmospheric Conditions and Perchlorate Brine Solutions". ACS Omega. 5 (16): 9391–9397. doi:10.1021/acsomega.0c00444. PMC 7191838. PMID 32363291.
  75. ^ "How Does Barometric Pressure Affect Humans?". MedicineNet.
  76. ^ Tarver, William J.; Volner, Keith; Cooper, Jeffrey S. (January 20, 2023). "Aerospace Pressure Effects". StatPearls. StatPearls Publishing. PMID 29262037 – via PubMed.
  77. ^ Complex life may be possible in only 10% of all galaxies, 24 Nov 2014, By Adrian Cho cience.org]
  78. ^ "Which Galaxies are Best Suited for the Evolution of Alien Life?". Discover Magazine.
  79. ^ "What's killing galaxies? Large survey reveals how star formation is shut down in extreme regions of the Universe".
  80. ^ Canada, National Research Council (November 2, 2021). "What's killing galaxies? Large survey reveals how star formation is shut down in extreme regions of the Universe". nrc.canada.ca.
  81. ^ "New study examines which galaxies are best for intelligent life". ScienceDaily.
  82. ^ a b Vera, Matias; Alonso, Sol; Coldwell, Georgina (November 1, 2016). "Effect of bars on the galaxy properties". Astronomy & Astrophysics. 595: A63. arXiv:1607.08643. Bibcode:2016A&A...595A..63V. doi:10.1051/0004-6361/201628750 – via www.aanda.org.
  83. ^ What is a peculiar galaxy?, Monthly Notices of the Royal Astronomical Society, Volume 286, Issue 4, April 1997, Pages 969–978, by O. Lahav and A. Nairn
  84. ^ "Star Formation in Irregular Galaxies". ned.ipac.caltech.edu.
  85. ^ "Irregular Galaxy: A Unique Collections of Stars – Let's Talk Stars". www.letstalkstars.com. February 17, 2023.
  86. ^ The connection between star formation and metallicity evolution in barred spiral galaxies, Monthly Notices of the Royal Astronomical Society, Volume 431, Issue 3, 21 May 2013, Pages 2560–2575, doi.org/10.1093/mnras/stt354, 20 March 2013
  87. ^ Yu, Si-Yue; Ho, Luis C. (January 31, 2019). "On the Connection between Spiral Arm Pitch Angle and Galaxy Properties". The Astrophysical Journal. 871 (2): 194. arXiv:1812.06010. Bibcode:2019ApJ...871..194Y. doi:10.3847/1538-4357/aaf895.
  88. ^ "What process creates and maintains the beautiful spiral arms around spiral galaxies? I've been told that density waves are responsible—so where do the density waves come from?". Scientific American.
  89. ^ Hall, Shannon. "The Milky Way's Spiral Arms May Have Carved Earth's Continents". Scientific American.
  90. ^ "The origin of elements, by Miller, astro.umd.edu" (PDF).
  91. ^ Mahoney, Trevor (July 13, 2020). "Why Different Types of Galaxies May Affect the Development of Life".
  92. ^ Mason, Paul (January 1, 2018). "The Supergalactic Habitable Zone". American Astronomical Society. 231: 401.04. Bibcode:2018AAS...23140104M – via NASA ADS.
  93. ^ Mason, P. A.; Biermann, P. L. (November 1, 2017). "The Large-Scale Structure of Habitability in the Universe". Habitable Worlds 2017. 2042: 4149. Bibcode:2017LPICo2042.4149M – via NASA ADS.
  94. ^ Mason, Paul (January 1, 2019). "The dawn of habitable conditions for complex life in the Universe". American Astronomical Society Meeting. 233: 432.06. Bibcode:2019AAS...23343206M – via NASA ADS.
  95. ^ "The Cosmic Blueprint | Paul Davies". cosmos.asu.edu.
  96. ^ "How plate tectonics have maintained Earth's 'Goldilocks' climate". The University of Sydney.
  97. ^ Ramirez, Ramses M. (May 4, 2020). "A Complex Life Habitable Zone Based On Lipid Solubility Theory". Scientific Reports. 10 (1): 7432. Bibcode:2020NatSR..10.7432R. doi:10.1038/s41598-020-64436-z. PMC 7198600. PMID 32366889.
  98. ^ "altvw102". www.npl.washington.edu.
  99. ^ Gribbin, John (2011). Alone in the Universe: Why our planet is unique. Wiley
  100. ^ Ward, Peter D.; Brownlee, Donald (2000). Rare Earth: Why Complex Life is Uncommon in the Universe. Copernicus Books (Springer Verlag). ISBN 978-0-387-98701-9.
  101. ^ Gonzales, Guillermo; Richards, Jay W (2004). The Privileged Planet. Regnery Publishing, Inc.
  102. ^ "Lucky Planet - Why Earth is Exceptional & Life In The Universe".
  103. ^ "The origin and rise of complex life | Royal Society". royalsociety.org. 7 December 2022.
  104. ^ "Ice, Snow, and Glaciers and the Water Cycle | U.S. Geological Survey". www.usgs.gov.
  105. ^ Deitrick, Russell; Barnes, Rory; Quinn, Thomas R.; Armstrong, John; Charnay, Benjamin; Wilhelm, Caitlyn (January 16, 2018). "Exo-Milankovitch Cycles. I. Orbits and Rotation States". The Astronomical Journal. 155 (2): 60. arXiv:1712.10060. Bibcode:2018AJ....155...60D. doi:10.3847/1538-3881/aaa301.
  106. ^ Deitrick, Russell; Barnes, Rory; Bitz, Cecilia; Fleming, David; Charnay, Benjamin; Meadows, Victoria; Wilhelm, Caitlyn; Armstrong, John; Quinn, Thomas R. (June 1, 2018). "Exo-Milankovitch Cycles. II. Climates of G-dwarf Planets in Dynamically Hot Systems". The Astronomical Journal. 155 (6): 266. arXiv:1805.00283. Bibcode:2018AJ....155..266D. doi:10.3847/1538-3881/aac214.
  107. ^ Tereza Pultarova (June 14, 2022). "Milankovitch cycles: What are they and how do they affect Earth?". Space.com.
  108. ^ Laboratory, By Alan Buis, NASA's Jet Propulsion. "Milankovitch (Orbital) Cycles and Their Role in Earth's Climate". Climate Change: Vital Signs of the Planet.((cite web)): CS1 maint: multiple names: authors list (link)
  109. ^ "Knowledge reference for national forest assessments – modeling for estimation and monitoring". www.fao.org. Archived from the original on January 13, 2020. Retrieved Feb 20, 2019.
  110. ^ Allison, Steven D.; Vitousek, Peter M. (2005-05-01). "Responses of extracellular enzymes to simple and complex nutrient inputs". Soil Biology and Biochemistry. 37 (5): 937–944. doi:10.1016/j.soilbio.2004.09.014. ISSN 0038-0717.
  111. ^ "Astrobiology". Biology Cabinet. September 26, 2006. Retrieved 2011-01-17.
  112. ^ "Polycyclic Aromatic Hydrocarbons: An Interview With Dr. Farid Salama". Astrobiology magazine. 2000. Archived from the original on 2008-06-20. Retrieved 2008-10-20.
  113. ^ Lipkus, Alan H.; Yuan, Qiong; Lucas, Karen A.; et al. (2008). "Structural Diversity of Organic Chemistry. A Scaffold Analysis of the CAS Registry". The Journal of Organic Chemistry. 73 (12). American Chemical Society (ACS): 4443–4451. doi:10.1021/jo8001276. PMID 18505297.
  114. ^ Molnar, Charles; Gair, Jane (May 14, 2015). "2.3 Biological Molecules". Introduction to the Chemistry of Life – via opentextbc.ca.
  115. ^ Education (2010). "CHNOPS: The Six Most Abundant Elements of Life". Pearson Education. Pearson BioCoach. Archived from the original on 27 July 2017. Retrieved 2010-12-10. Most biological molecules are made from covalent combinations of six important elements, whose chemical symbols are CHNOPS. ... Although more than 25 types of elements can be found in biomolecules, six elements are most common. These are called the CHNOPS elements; the letters stand for the chemical abbreviations of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.