Drake equation (English Wikipedia)

Physics Today 14 (4), 40–46 (1961). Drake, F. D. (April 1961). "Project Ozma". Physics Today. 14 (4). American Institute of Physics: 40–46. Bibcode:1961PhT....14d..40D. doi:10.1063/1.3057500. Retrieved 27 April 2023. The question of the existence of intelligent life elsewhere in space has long fascinated people, but, until recently, has been properly left to the science‐fiction writers.

archive.org (Global: 6^th place; English: 6^th place)

Bonner, J. T. (1988). The evolution of complexity by means of natural selection. Princeton University Press. ISBN 0-691-08494-7.

archives-ouvertes.fr (Global: 1,143^rd place; English: 973^rd place)

hal.archives-ouvertes.fr

Selsis, Franck; Kasting, James F.; Levrard, Benjamin; Paillet, Jimmy; Ribas, Ignasi; Delfosse, Xavier (2007). "Habitable planets around the star Gl 581?". Astronomy and Astrophysics. 476 (3): 1373–1387. arXiv:0710.5294. Bibcode:2007A&A...476.1373S. doi:10.1051/0004-6361:20078091. S2CID 11492499.

arxiv.org (Global: 49^th place; English: 31^st place)

Glade, N.; Ballet, P.; Bastien, O. (2012). "A stochastic process approach of the drake equation parameters". International Journal of Astrobiology. 11 (2): 103–108. arXiv:1112.1506. Bibcode:2012IJAsB..11..103G. doi:10.1017/S1473550411000413. S2CID 119250730. Note: This reference has a table of 1961 values, claimed to be taken from Drake & Sobel, but these differ from the book.
Robitaille, Thomas P.; Barbara A. Whitney (2010). "The present-day star formation rate of the Milky Way determined from Spitzer-detected young stellar objects". The Astrophysical Journal Letters. 710 (1): L11. arXiv:1001.3672. Bibcode:2010ApJ...710L..11R. doi:10.1088/2041-8205/710/1/L11. S2CID 118703635.
Kennicutt, Robert C.; Evans, Neal J. (22 September 2012). "Star Formation in the Milky Way and Nearby Galaxies". Annual Review of Astronomy and Astrophysics. 50 (1): 531–608. arXiv:1204.3552. Bibcode:2012ARA&A..50..531K. doi:10.1146/annurev-astro-081811-125610. S2CID 118667387.
Cassan, A.; et al. (11 January 2012). "One or more bound planets per Milky Way star from microlensing observations". Nature. 481 (7380): 167–169. arXiv:1202.0903. Bibcode:2012Natur.481..167C. doi:10.1038/nature10684. PMID 22237108. S2CID 2614136.
Petigura, Eric A.; Howard, Andrew W.; Marcy, Geoffrey W. (31 October 2013). "Prevalence of Earth-size planets orbiting Sun-like stars". Proceedings of the National Academy of Sciences of the United States of America. 110 (48): 19273–19278. arXiv:1311.6806. Bibcode:2013PNAS..11019273P. doi:10.1073/pnas.1319909110. PMC 3845182. PMID 24191033.
Lineweaver, C. H.; Fenner, Y.; Gibson, B. K. (2004). "The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way". Science. 303 (5654): 59–62. arXiv:astro-ph/0401024. Bibcode:2004Sci...303...59L. doi:10.1126/science.1092322. PMID 14704421. S2CID 18140737.
Dressing, C. D.; Charbonneau, D. (2013). "The Occurrence Rate of Small Planets around Small Stars". The Astrophysical Journal. 767 (1): 95. arXiv:1302.1647. Bibcode:2013ApJ...767...95D. doi:10.1088/0004-637X/767/1/95. S2CID 29441006.
Heller, René; Barnes, Rory (29 April 2014). "Constraints on the Habitability of Extrasolar Moons". Proceedings of the International Astronomical Union. 8 (S293): 159–164. arXiv:1210.5172. Bibcode:2014IAUS..293..159H. doi:10.1017/S1743921313012738. S2CID 92988047.
Westby, Tom; Conselice, Christopher J. (15 June 2020). "The Astrobiological Copernican Weak and Strong Limits for Intelligent Life". The Astrophysical Journal. 896 (1): 58. arXiv:2004.03968. Bibcode:2020ApJ...896...58W. doi:10.3847/1538-4357/ab8225. S2CID 215415788.
Kipping, David (18 May 2020). "An objective Bayesian analysis of life's early start and our late arrival". Proceedings of the National Academy of Sciences. 117 (22): 11995–12003. arXiv:2005.09008. Bibcode:2020PNAS..11711995K. doi:10.1073/pnas.1921655117. PMC 7275750. PMID 32424083.
Forgan, D.; Elvis, M. (2011). "Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence". International Journal of Astrobiology. 10 (4): 307–313. arXiv:1103.5369. Bibcode:2011IJAsB..10..307F. doi:10.1017/S1473550411000127. S2CID 119111392.
von Bloh, W.; Bounama, C.; Cuntz, M.; Franck, S. (2007). "The habitability of super-Earths in Gliese 581". Astronomy & Astrophysics. 476 (3): 1365–1371. arXiv:0705.3758. Bibcode:2007A&A...476.1365V. doi:10.1051/0004-6361:20077939. S2CID 14475537.
Selsis, Franck; Kasting, James F.; Levrard, Benjamin; Paillet, Jimmy; Ribas, Ignasi; Delfosse, Xavier (2007). "Habitable planets around the star Gl 581?". Astronomy and Astrophysics. 476 (3): 1373–1387. arXiv:0710.5294. Bibcode:2007A&A...476.1373S. doi:10.1051/0004-6361:20078091. S2CID 11492499.
Lineweaver, C. H.; Davis, T. M. (2002). "Does the rapid appearance of life on Earth suggest that life is common in the universe?". Astrobiology. 2 (3): 293–304. arXiv:astro-ph/0205014. Bibcode:2002AsBio...2..293L. doi:10.1089/153110702762027871. PMID 12530239. S2CID 431699.
Forgan, D. (2009). "A numerical testbed for hypotheses of extraterrestrial life and intelligence". International Journal of Astrobiology. 8 (2): 121–131. arXiv:0810.2222. Bibcode:2009IJAsB...8..121F. doi:10.1017/S1473550408004321. S2CID 17469638.
Frank, Adam; Sullivan III, W. T. (22 April 2016). "A New Empirical Constraint on the Prevalence of Technological Species in the Universe". Astrobiology. 16 (5) (published 13 May 2016): 359–362. arXiv:1510.08837. Bibcode:2016AsBio..16..359F. doi:10.1089/ast.2015.1418. PMID 27105054.
Christopher J. Conselice; et al. (2016). "The Evolution of Galaxy Number Density at $z < 8$ and its Implications". The Astrophysical Journal. 830 (2): 83. arXiv:1607.03909. Bibcode:2016ApJ...830...83C. doi:10.3847/0004-637X/830/2/83. S2CID 17424588.
Sandberg, Anders; Drexler, Eric; Ord, Toby (6 June 2018). "Dissolving the Fermi Paradox". arXiv:1806.02404 [physics.pop-ph].

astro-tom.com (Global: low place; English: low place)

Schilling, Govert (November 2011). "The Chance of Finding Aliens: Reevaluating the Drake Equation". astro-tom.com.

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SETI: A celebration of the first 50 years. Keith Cooper. Astronomy Now. 2000

bbc.co.uk (Global: 11^th place; English: 10^th place)

Palmer, J. (11 January 2012). "Exoplanets are around every star, study suggests". BBC. Retrieved 12 January 2012.

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"The unsurprising non-detection of intelligent aliens". Big Think. 23 April 2024. Retrieved 29 April 2024.

books.google.com (Global: 3^rd place; English: 3^rd place)

Wanjek, C. (2015). The Drake Equation. Cambridge University Press. ISBN 9781107073654. Retrieved 9 September 2016.
Webb, S. (2015). If the Universe Is Teeming with Aliens ... WHERE IS EVERYBODY?: Seventy-Five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life. Springer International Publishing. ISBN 978-3319132358.

brin-l.com (Global: low place; English: low place)

Brin, G. D. (1983). "The Great Silence – The Controversy Concerning Extraterrestrial Intelligent Life" (PDF). Quarterly Journal of the Royal Astronomical Society. 24 (3): 283–309. Bibcode:1983QJRAS..24..283B.

cosmosmagazine.com (Global: low place; English: low place)

^{[better source needed]} Dean, T. (10 August 2009). "A review of the Drake Equation". Cosmos Magazine. Archived from the original on 3 June 2013. Retrieved 16 April 2013.

cplire.ru (Global: low place; English: low place)

Zaitsev, A. (May 2005). "The Drake Equation: Adding a METI Factor". SETI League. Retrieved 20 April 2013.

csicop.org (Global: 5,333^rd place; English: 3,752^nd place)

Tarter, Jill C. (May–June 2006). "The Cosmic Haystack Is Large". Skeptical Inquirer. 30 (3). Retrieved 21 August 2013.

daviddarling.info (Global: 8,448^th place; English: low place)

Darling, D. J. "Green Bank conference (1961)". The Encyclopedia of Science. Archived from the original on 21 February 2024. Retrieved 13 August 2013.

doi.org (Global: 2^nd place; English: 2^nd place)

Physics Today 14 (4), 40–46 (1961). Drake, F. D. (April 1961). "Project Ozma". Physics Today. 14 (4). American Institute of Physics: 40–46. Bibcode:1961PhT....14d..40D. doi:10.1063/1.3057500. Retrieved 27 April 2023. The question of the existence of intelligent life elsewhere in space has long fascinated people, but, until recently, has been properly left to the science‐fiction writers.
Burchell, M. J. (2006). "W(h)ither the Drake equation?". International Journal of Astrobiology. 5 (3): 243–250. Bibcode:2006IJAsB...5..243B. doi:10.1017/S1473550406003107. S2CID 121060763.
Glade, N.; Ballet, P.; Bastien, O. (2012). "A stochastic process approach of the drake equation parameters". International Journal of Astrobiology. 11 (2): 103–108. arXiv:1112.1506. Bibcode:2012IJAsB..11..103G. doi:10.1017/S1473550411000413. S2CID 119250730. Note: This reference has a table of 1961 values, claimed to be taken from Drake & Sobel, but these differ from the book.
Cocconi, G.; Morisson, P. (1959). "Searching for Interstellar Communications" (PDF). Nature. 184 (4690): 844–846. Bibcode:1959Natur.184..844C. doi:10.1038/184844a0. S2CID 4220318. Archived (PDF) from the original on 28 July 2011. Retrieved 10 April 2013.
Robitaille, Thomas P.; Barbara A. Whitney (2010). "The present-day star formation rate of the Milky Way determined from Spitzer-detected young stellar objects". The Astrophysical Journal Letters. 710 (1): L11. arXiv:1001.3672. Bibcode:2010ApJ...710L..11R. doi:10.1088/2041-8205/710/1/L11. S2CID 118703635.
Kennicutt, Robert C.; Evans, Neal J. (22 September 2012). "Star Formation in the Milky Way and Nearby Galaxies". Annual Review of Astronomy and Astrophysics. 50 (1): 531–608. arXiv:1204.3552. Bibcode:2012ARA&A..50..531K. doi:10.1146/annurev-astro-081811-125610. S2CID 118667387.
Cassan, A.; et al. (11 January 2012). "One or more bound planets per Milky Way star from microlensing observations". Nature. 481 (7380): 167–169. arXiv:1202.0903. Bibcode:2012Natur.481..167C. doi:10.1038/nature10684. PMID 22237108. S2CID 2614136.
Petigura, Eric A.; Howard, Andrew W.; Marcy, Geoffrey W. (31 October 2013). "Prevalence of Earth-size planets orbiting Sun-like stars". Proceedings of the National Academy of Sciences of the United States of America. 110 (48): 19273–19278. arXiv:1311.6806. Bibcode:2013PNAS..11019273P. doi:10.1073/pnas.1319909110. PMC 3845182. PMID 24191033.
Trimble, V. (1997). "Origin of the biologically important elements". Origins of Life and Evolution of the Biosphere. 27 (1–3): 3–21. Bibcode:1997OLEB...27....3T. doi:10.1023/A:1006561811750. PMID 9150565. S2CID 7612499.
Lineweaver, C. H.; Fenner, Y.; Gibson, B. K. (2004). "The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way". Science. 303 (5654): 59–62. arXiv:astro-ph/0401024. Bibcode:2004Sci...303...59L. doi:10.1126/science.1092322. PMID 14704421. S2CID 18140737.
Dressing, C. D.; Charbonneau, D. (2013). "The Occurrence Rate of Small Planets around Small Stars". The Astrophysical Journal. 767 (1): 95. arXiv:1302.1647. Bibcode:2013ApJ...767...95D. doi:10.1088/0004-637X/767/1/95. S2CID 29441006.
Heller, René; Barnes, Rory (29 April 2014). "Constraints on the Habitability of Extrasolar Moons". Proceedings of the International Astronomical Union. 8 (S293): 159–164. arXiv:1210.5172. Bibcode:2014IAUS..293..159H. doi:10.1017/S1743921313012738. S2CID 92988047.
Davies, P. (2007). "Are Aliens Among Us?". Scientific American. 297 (6): 62–69. Bibcode:2007SciAm.297f..62D. doi:10.1038/scientificamerican1207-62.
Crick, F. H. C.; Orgel, L. E. (1973). "Directed Panspermia" (PDF). Icarus. 19 (3): 341–346. Bibcode:1973Icar...19..341C. doi:10.1016/0019-1035(73)90110-3. Archived from the original (PDF) on 29 October 2011.
Westby, Tom; Conselice, Christopher J. (15 June 2020). "The Astrobiological Copernican Weak and Strong Limits for Intelligent Life". The Astrophysical Journal. 896 (1): 58. arXiv:2004.03968. Bibcode:2020ApJ...896...58W. doi:10.3847/1538-4357/ab8225. S2CID 215415788.
Muro, Enrique M.; Ballesteros, Fernando J.; Luque, Bartolo; Bascompte, Jordi (2025). "The emergence of eukaryotes as an evolutionary algorithmic phase transition". PNAS. 122 (13) e2422968122. Bibcode:2025PNAS..12222968M. doi:10.1073/pnas.2422968122. PMC 12002324. PMID 40146859.
Kipping, David (18 May 2020). "An objective Bayesian analysis of life's early start and our late arrival". Proceedings of the National Academy of Sciences. 117 (22): 11995–12003. arXiv:2005.09008. Bibcode:2020PNAS..11711995K. doi:10.1073/pnas.1921655117. PMC 7275750. PMID 32424083.
Forgan, D.; Elvis, M. (2011). "Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence". International Journal of Astrobiology. 10 (4): 307–313. arXiv:1103.5369. Bibcode:2011IJAsB..10..307F. doi:10.1017/S1473550411000127. S2CID 119111392.
Tarter, Jill C. (September 2001). "The Search for Extraterrestrial Intelligence (SETI)". Annual Review of Astronomy and Astrophysics. 39: 511–548. Bibcode:2001ARA&A..39..511T. doi:10.1146/annurev.astro.39.1.511. S2CID 261531924.
Shermer, M. (August 2002). "Why ET Hasn't Called". Scientific American. 287 (2): 21. Bibcode:2002SciAm.287b..33S. doi:10.1038/scientificamerican0802-33.
Vinn, O. (2024). "Potential incompatibility of inherited behavior patterns with civilization: Implications for Fermi paradox". Science Progress. 107 (3) 00368504241272491: 1–6. doi:10.1177/00368504241272491. PMC 11307330. PMID 39105260.
"The value of $N$ remains highly uncertain. Even if we had a perfect knowledge of the first two terms in the equation, there are still five remaining terms, each of which could be uncertain by factors of 1,000." from Wilson, TL (2001). "The search for extraterrestrial intelligence". Nature. 409 (6823). Nature Publishing Group: 1110–1114. Bibcode:2001Natur.409.1110W. doi:10.1038/35059235. PMID 11234025. S2CID 205014501., or more informally, "The Drake Equation can have any value from "billions and billions" to zero", Michael Crichton, as quoted in Douglas A. Vakoch; et al. (2015). The Drake Equation: Estimating the prevalence of extraterrestrial life through the ages. Cambridge University Press. ISBN 978-1-10-707365-4., p. 13
von Bloh, W.; Bounama, C.; Cuntz, M.; Franck, S. (2007). "The habitability of super-Earths in Gliese 581". Astronomy & Astrophysics. 476 (3): 1365–1371. arXiv:0705.3758. Bibcode:2007A&A...476.1365V. doi:10.1051/0004-6361:20077939. S2CID 14475537.
Selsis, Franck; Kasting, James F.; Levrard, Benjamin; Paillet, Jimmy; Ribas, Ignasi; Delfosse, Xavier (2007). "Habitable planets around the star Gl 581?". Astronomy and Astrophysics. 476 (3): 1373–1387. arXiv:0710.5294. Bibcode:2007A&A...476.1373S. doi:10.1051/0004-6361:20078091. S2CID 11492499.
Lineweaver, C. H.; Davis, T. M. (2002). "Does the rapid appearance of life on Earth suggest that life is common in the universe?". Astrobiology. 2 (3): 293–304. arXiv:astro-ph/0205014. Bibcode:2002AsBio...2..293L. doi:10.1089/153110702762027871. PMID 12530239. S2CID 431699.
Forgan, D. (2009). "A numerical testbed for hypotheses of extraterrestrial life and intelligence". International Journal of Astrobiology. 8 (2): 121–131. arXiv:0810.2222. Bibcode:2009IJAsB...8..121F. doi:10.1017/S1473550408004321. S2CID 17469638.
Frank, Adam; Sullivan III, W. T. (22 April 2016). "A New Empirical Constraint on the Prevalence of Technological Species in the Universe". Astrobiology. 16 (5) (published 13 May 2016): 359–362. arXiv:1510.08837. Bibcode:2016AsBio..16..359F. doi:10.1089/ast.2015.1418. PMID 27105054.
Maccone, C. (2010). "The Statistical Drake Equation". Acta Astronautica. 67 (11–12): 1366–1383. Bibcode:2010AcAau..67.1366M. doi:10.1016/j.actaastro.2010.05.003. S2CID 121239391.
Golden, Leslie M. (1 August 2021). "A joint mind consideration of the Drake equation in the search for extraterrestrial intelligence". Acta Astronautica. 185: 333–336. Bibcode:2021AcAau.185..333G. doi:10.1016/j.actaastro.2021.03.020. ISSN 0094-5765. S2CID 233663920.
Stern, Robert J.; Gerya, Taras V. (12 April 2024). "The importance of continents, oceans and plate tectonics for the evolution of complex life: implications for finding extraterrestrial civilizations". Scientific Reports. 14 (1): 8552. Bibcode:2024NatSR..14.8552S. doi:10.1038/s41598-024-54700-x. PMC 11015018. PMID 38609425.
Christopher J. Conselice; et al. (2016). "The Evolution of Galaxy Number Density at $z < 8$ and its Implications". The Astrophysical Journal. 830 (2): 83. arXiv:1607.03909. Bibcode:2016ApJ...830...83C. doi:10.3847/0004-637X/830/2/83. S2CID 17424588.
Jones, E. M. (1 March 1985). "Where is everybody?" An account of Fermi's question (PDF) (Report). Los Alamos National Laboratory. Bibcode:1985STIN...8530988J. doi:10.2172/5746675. OSTI 5746675. Archived (PDF) from the original on 12 October 2007. Retrieved 21 August 2013.

elte.hu (Global: 5,662^nd place; English: 8,968^th place)

astro.elte.hu

Hetesi, Z.; Regaly, Z. (2006). "A new interpretation of Drake-equation" (PDF). Journal of the British Interplanetary Society. 59: 11–14. Bibcode:2006JBIS...59...11H. Archived from the original (PDF) on 5 February 2009.

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ghostarchive.org (Global: 64^th place; English: 28^th place)

Overbye, Dennis (4 November 2013). "Far-Off Planets Like the Earth Dot the Galaxy". The New York Times. Archived from the original on 1 January 2022. Retrieved 5 November 2013.
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iaragroup.org (Global: low place; English: low place)

Cocconi, G.; Morisson, P. (1959). "Searching for Interstellar Communications" (PDF). Nature. 184 (4690): 844–846. Bibcode:1959Natur.184..844C. doi:10.1038/184844a0. S2CID 4220318. Archived (PDF) from the original on 28 July 2011. Retrieved 10 April 2013.

independent.co.uk (Global: 46^th place; English: 29^th place)

Sulleyman, Aatif (2 November 2017). "Stephen Hawking warns artificial intelligence 'may replace humans altogether'". independent.co.uk.

io9.com (Global: 4,391^st place; English: 2,871^st place)

"A New Equation Reveals Our Exact Odds of Finding Alien Life". io9. 21 June 2013.

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"The Drake Equation". phys.libretexts.org. 13 August 2014. Retrieved 4 February 2024.

michaelshermer.com (Global: low place; English: low place)

Shermer, M. (August 2002). "Why ET Hasn't Called". Scientific American. 287 (2): 21. Bibcode:2002SciAm.287b..33S. doi:10.1038/scientificamerican0802-33.

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jpl.nasa.gov

"NASA Unveils Design for Message Heading to Jupiter's Moon Europa". NASA Jet Propulsion Laboratory (JPL). Retrieved 11 March 2024. This article incorporates text from this source, which is in the public domain.

nationalgeographic.com (Global: 489^th place; English: 425^th place)

news.nationalgeographic.com

Drake, N. (30 June 2014). "How my Dad's Equation Sparked the Search for Extraterrestrial Intelligence". National Geographic. Archived from the original on 5 July 2014. Retrieved 2 October 2016.

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"Life On Other Planets?". Sydney Morning Herald. 8 November 1959. Retrieved 2 October 2015.

nih.gov (Global: 5^th place; English: 5^th place)

pubmed.ncbi.nlm.nih.gov

Cassan, A.; et al. (11 January 2012). "One or more bound planets per Milky Way star from microlensing observations". Nature. 481 (7380): 167–169. arXiv:1202.0903. Bibcode:2012Natur.481..167C. doi:10.1038/nature10684. PMID 22237108. S2CID 2614136.
Petigura, Eric A.; Howard, Andrew W.; Marcy, Geoffrey W. (31 October 2013). "Prevalence of Earth-size planets orbiting Sun-like stars". Proceedings of the National Academy of Sciences of the United States of America. 110 (48): 19273–19278. arXiv:1311.6806. Bibcode:2013PNAS..11019273P. doi:10.1073/pnas.1319909110. PMC 3845182. PMID 24191033.
Trimble, V. (1997). "Origin of the biologically important elements". Origins of Life and Evolution of the Biosphere. 27 (1–3): 3–21. Bibcode:1997OLEB...27....3T. doi:10.1023/A:1006561811750. PMID 9150565. S2CID 7612499.
Lineweaver, C. H.; Fenner, Y.; Gibson, B. K. (2004). "The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way". Science. 303 (5654): 59–62. arXiv:astro-ph/0401024. Bibcode:2004Sci...303...59L. doi:10.1126/science.1092322. PMID 14704421. S2CID 18140737.
Muro, Enrique M.; Ballesteros, Fernando J.; Luque, Bartolo; Bascompte, Jordi (2025). "The emergence of eukaryotes as an evolutionary algorithmic phase transition". PNAS. 122 (13) e2422968122. Bibcode:2025PNAS..12222968M. doi:10.1073/pnas.2422968122. PMC 12002324. PMID 40146859.
Kipping, David (18 May 2020). "An objective Bayesian analysis of life's early start and our late arrival". Proceedings of the National Academy of Sciences. 117 (22): 11995–12003. arXiv:2005.09008. Bibcode:2020PNAS..11711995K. doi:10.1073/pnas.1921655117. PMC 7275750. PMID 32424083.
Vinn, O. (2024). "Potential incompatibility of inherited behavior patterns with civilization: Implications for Fermi paradox". Science Progress. 107 (3) 00368504241272491: 1–6. doi:10.1177/00368504241272491. PMC 11307330. PMID 39105260.
"The value of $N$ remains highly uncertain. Even if we had a perfect knowledge of the first two terms in the equation, there are still five remaining terms, each of which could be uncertain by factors of 1,000." from Wilson, TL (2001). "The search for extraterrestrial intelligence". Nature. 409 (6823). Nature Publishing Group: 1110–1114. Bibcode:2001Natur.409.1110W. doi:10.1038/35059235. PMID 11234025. S2CID 205014501., or more informally, "The Drake Equation can have any value from "billions and billions" to zero", Michael Crichton, as quoted in Douglas A. Vakoch; et al. (2015). The Drake Equation: Estimating the prevalence of extraterrestrial life through the ages. Cambridge University Press. ISBN 978-1-10-707365-4., p. 13
Lineweaver, C. H.; Davis, T. M. (2002). "Does the rapid appearance of life on Earth suggest that life is common in the universe?". Astrobiology. 2 (3): 293–304. arXiv:astro-ph/0205014. Bibcode:2002AsBio...2..293L. doi:10.1089/153110702762027871. PMID 12530239. S2CID 431699.
Frank, Adam; Sullivan III, W. T. (22 April 2016). "A New Empirical Constraint on the Prevalence of Technological Species in the Universe". Astrobiology. 16 (5) (published 13 May 2016): 359–362. arXiv:1510.08837. Bibcode:2016AsBio..16..359F. doi:10.1089/ast.2015.1418. PMID 27105054.
Stern, Robert J.; Gerya, Taras V. (12 April 2024). "The importance of continents, oceans and plate tectonics for the evolution of complex life: implications for finding extraterrestrial civilizations". Scientific Reports. 14 (1): 8552. Bibcode:2024NatSR..14.8552S. doi:10.1038/s41598-024-54700-x. PMC 11015018. PMID 38609425.

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Petigura, Eric A.; Howard, Andrew W.; Marcy, Geoffrey W. (31 October 2013). "Prevalence of Earth-size planets orbiting Sun-like stars". Proceedings of the National Academy of Sciences of the United States of America. 110 (48): 19273–19278. arXiv:1311.6806. Bibcode:2013PNAS..11019273P. doi:10.1073/pnas.1319909110. PMC 3845182. PMID 24191033.
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