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1 Introduction
Pages 5-10

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From page 5...
... That priority reflects public interest, which was enhanced in the mid-1990s when fragments of Mars delivered to Earth as meteorites were shown to contain small structures reminiscent of microbial life. The proper interpretation of those structures remains controversial, but it is certain that nothing would alter our view of humanity and our position in the cosmos more than the discovery of alien life.
From page 6...
... The biomolecules found in terran life appear to have molecular structures that create properties specifically suited to the demands imposed by water. • Living systems that have emerged on Earth have done so by a process of random variation in the structure of inherited biomolecules, on which was superimposed natural selection to achieve fitness.
From page 7...
... If the ability to undergo Darwinian evolution is a canonical trait of life no matter how different a life form is from Earth life, are there properties of evolving extraterrestrial organisms that would be detectable as positive signs of life? Evolution provides organisms the opportunity to exploit new and changing environments, and one piece of evidence for the cosmic ubiquity of evolution is that on Earth life occupies all available habitats and even creates new ones as a consequence of metabolism.
From page 8...
... Natural selection based solely on mutation is probably not an adequate mechanism for evolving complexity. More important, lateral gene transfer and endosymbiosis are probably the most obvious mechanisms for creating complex genomes that could lead to free-living cells and complex cellular communities in the short geological interval between life's origin and the establishment of autotrophic CO2 fixation about 3.8 billion years ago and microbial sulfate reduction 3.47 billion years ago on the basis of isotope data.
From page 9...
... Exploration of Earth has taken researchers to environments that human-like organisms find extreme, to the highest temperatures at which liquid water is possible, to the lowest temperatures at which water is liquid, to the depths of the ocean where pressures are high, to extremes of acidity and alkalinity, to places where the energy flux is too high for human-like life to survive, to locales where thermodynamic disequilibria are too scarce to support human-like life, and to locations where the chemical environment is toxic to human-like life. The committee then asked, Can we identify environments on Earth where Darwinian processes that exploit human-like biochemistry cannot exploit available thermodynamic disequilibria?
From page 10...
... 13. Adami, C., and Wilke, C.O., 2004, Experiments in digital life, Artificial Life 10:117-122; Rosing, M.T., 1999, 13C-depleted carbon microparticles in >3700-Ma sea-floor sedimentary rocks from West Greenland, Science 283:674-676; Shen, Y., Buick, R., and Canfield, D.E., 2001, Isotopic evidence for microbial sulphate reduction in the early Archaean era, Nature 410:77-81; and Shidlowski, M.A., 1988, A 3800-million-year isotopic record of life from carbon in sedimentary rocks, Nature 333:313-318.


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