Finding a second sample of life on earth.

If life emerges readily under Earth-like conditions, the possibility arises of multiple terrestrial genesis events. We seek to quantify the probability of this scenario using estimates of the Archean bombardment rate and the fact that life established itself fairly rapidly on Earth once conditions became favorable. We find a significant likelihood that at least one more sample of life, referred to here as alien life, may have emerged on Earth, and could have coexisted with known life. Indeed, it is difficult to rule out the possibility of extant alien life. We offer some suggestions for how an alternative sample of life might be detected.

[1]  Cosmic Thermobiology: Thermal Constraints on the Origin and Evolution of Life in the Universe , 2003, astro-ph/0305214.

[2]  J. H. Strauss,et al.  Virus Evolution , 2001, Cell.

[3]  Robert L. Folk,et al.  SEM imaging of bacteria and nannobacteria in carbonate sediments and rocks , 1993 .

[4]  Ernest L. Eliel,et al.  Stereochemistry of Organic Compounds , 1962 .

[5]  J. Bada.  Biogeochemistry of Organic Nitrogen Compounds , 1998 .

[6]  N. Pace.  A molecular view of microbial diversity and the biosphere. , 1997, Science.

[7]  A. Cairns-smith.  Genetic takeover and the mineral origins of life , 1982 .

[8]  D. Lovley,et al.  Extending the Upper Temperature Limit for Life , 2003, Science.

[9]  Paul Davies,et al.  The Fifth Miracle , 2004 .

[10]  Philip M. Novack-Gottshall,et al.  Effects of sampling standardization on estimates of Phanerozoic marine diversification , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[11]  R Buick,et al.  Archean molecular fossils and the early rise of eukaryotes. , 1999, Science.

[12]  Matthew Prior,et al.  Letter from “J” , 1863, The Dental register.

[13]  B. Carter.  The anthropic principle and its implications for biological evolution , 1983, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[14]  N. Sleep,et al.  Impacts and the Early Evolution of Life , 2006 .

[15]  N. Sleep,et al.  Initiation of clement surface conditions on the earliest Earth , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[16]  F. Casadei,et al.  Protective effect of clay minerals on adsorbed nucleic acid against UV radiation: possible role in the origin of life , 2004, International Journal of Astrobiology.

[17]  C. Woese.  The universal ancestor. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[18]  D. Catling.  EVOLUTION OF ATMOSPHERIC OXYGEN , 2003 .

[19]  Patricio Jeraldo,et al.  The Genetic Code , 2006 .

[20]  Simonetta Gribaldo,et al.  The Root of the Universal Tree of Life Inferred from Anciently Duplicated Genes Encoding Components of the Protein-Targeting Machinery , 1998, Journal of Molecular Evolution.

[21]  F. Dewhirst,et al.  Identification of oral streptococci using PCR-based, reverse-capture, checkerboard hybridization , 1998 .

[22]  T. Davis,et al.  Does the rapid appearance of life on Earth suggest that life is common in the universe? , 2002, Astrobiology.

[23]  William K. Hartmann,et al.  The Time-Dependent Intense Bombardment of the Primordial Earth/Moon System , 2000 .

[24]  L. Hurst,et al.  The Genetic Code Is One in a Million , 1998, Journal of Molecular Evolution.

[25]  N. C. Wickramasinghe,et al.  Astronomical origins of life : steps towards panspermia , 2000 .

[26]  David J. Stevenson,et al.  Impact frustration of the origin of life , 1988, Nature.

[27]  O. Kandler,et al.  Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya. , 1990, Proceedings of the National Academy of Sciences of the United States of America.

[28]  J. O'keefe.  The origin of the moon and the core of the earth. , 1966 .

[29]  Jared R Leadbetter,et al.  Cultivation of recalcitrant microbes: cells are alive, well and revealing their secrets in the 21st century laboratory. , 2003, Current opinion in microbiology.

[30]  Christopher P. McKay,et al.  Mars-Like Soils in the Atacama Desert, Chile, and the Dry Limit of Microbial Life , 2003, Science.

[31]  J. Kasting,et al.  New insights into Archean sulfur cycle from mass-independent sulfur isotope records from the Hamersley Basin, Australia , 2003 .

[32]  Antonio Lazcano,et al.  How long did it take for life to begin and evolve to cyanobacteria? , 1994, Journal of Molecular Evolution.

[33]  J L Bada,et al.  Preservation of key biomolecules in the fossil record: current knowledge and future challenges. , 1999, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[34]  Richard I. Webb,et al.  NOVEL NANO-ORGANISMS FROM AUSTRALIAN SANDSTONES , 1998 .

[35]  Harald Huber,et al.  A new phylum of Archaea represented by a nanosized hyperthermophilic symbiont , 2002, Nature.

[36]  W. Doolittle,et al.  Biodiversity: Something new under the sea , 2002, Nature.

[37]  D M Raup,et al.  Periodic extinction of families and genera. , 1986, Science.

[38]  Harold J. Morowitz,et al.  Annihilation of ecosystems by large asteroid impacts on the early Earth , 1989, Nature.

[39]  H. Melosh,et al.  The origin of the moon and the single-impact hypothesis III. , 1991, Icarus.

[40]  C. Darwin.  The Life and Letters of Charles Darwin , 1959, The Yale Journal of Biology and Medicine.

[41]  V. Oberbeck,et al.  Estimates of the maximum time required to originate life , 2005, Origins of life and evolution of the biosphere.