{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,14]],"date-time":"2026-10-14T19:37:21Z","timestamp":1792006641780,"version":"4.4.0"},"reference-count":118,"publisher":"American Association for the Advancement of Science (AAAS)","issue":"4967","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Science"],"published-print":{"date-parts":[[1990,7,27]]},"abstract":"<jats:p>\n                    It has long been speculated that Earth accreted prebiotic organic molecules important for the origins of life from impacts of carbonaceous asteroids and comets during the period of heavy bombardment 4.5 \u00d7 10\n                    <jats:sup>9<\/jats:sup>\n                    to 3.8 \u00d7 10\n                    <jats:sup>9<\/jats:sup>\n                    years ago. A comprehensive treatment of comet-asteroid interaction with the atmosphere, surface impact, and resulting organic pyrolysis demonstrates that organics will not survive impacts at velocities greater than about 10 kilometers per second and that even comets and asteroids as small as 100 meters in radius cannot be aerobraked to below this velocity in 1-bar atmospheres. However, for plausible dense (10-bar carbon dioxide) early atmospheres, we find that 4.5 \u00d7 10\n                    <jats:sup>9<\/jats:sup>\n                    years ago Earth was accreting intact cometary organics at a rate of at least \u223c10\n                    <jats:sup>6<\/jats:sup>\n                    to 10\n                    <jats:sup>7<\/jats:sup>\n                    kilograms per year, a flux that thereafter declined with a half-life of \u223c10\n                    <jats:sup>8<\/jats:sup>\n                    years. These results may be put in context by comparison with terrestrial oceanic and total biomasses, \u223c3 \u00d7 10\n                    <jats:sup>12<\/jats:sup>\n                    kilograms and \u223c6 \u00d7 10\n                    <jats:sup>14<\/jats:sup>\n                    kilograms, respectively.\n                  <\/jats:p>","DOI":"10.1126\/science.11538074","type":"journal-article","created":{"date-parts":[[2006,10,5]],"date-time":"2006-10-05T18:10:14Z","timestamp":1160071814000},"page":"366-373","source":"Crossref","is-referenced-by-count":512,"title":["Cometary Delivery of Organic Molecules to the Early Earth"],"prefix":"10.1126","volume":"249","author":[{"given":"Christopher F.","family":"Chyba","sequence":"first","affiliation":[{"name":"Laboratory for Planetary Studies, Cornell University, Ithaca, NY 14853, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Paul J.","family":"Thomas","sequence":"additional","affiliation":[{"name":"Laboratory for Planetary Studies, Cornell University, Ithaca, NY 14853, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Leigh","family":"Brookshaw","sequence":"additional","affiliation":[{"name":"Section of Applied Physics, Yale University, Box 2159, Yale Station, New Haven, CIT 06520."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Carl","family":"Sagan","sequence":"additional","affiliation":[{"name":"Laboratory for Planetary Studies, Cornell University, Ithaca, NY 14853, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"221","reference":[{"key":"e_1_2_1_1_1","unstructured":"Sesame '83: Report on the Los Alamos Equation-of-State Library (1983)."},{"key":"e_1_2_1_2_1","first-page":"79","year":"1959","unstructured":"Abelson, P. 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