Astroparticle Physics

288 14 Astrobiologyage of life on Earthbioastronomymasses of quarksThe oldest sedimentary rocks on Earth (3.9 × 10 9 yearsold) contain fossiles of cells. It is known that bacteria evenexisted 3.5 × 10 9 years ago. If the biological evolution hadrequired extremely long time scales, it is conceivable thatthe development of the higher forms of life would have beenimpossible, since the fuel of stars typically only lasts for10 10 years.The origin of life is a question of much debate. In additionto the theory of a terrestrial origin also the notion ofextra-terrestrial delivery of organic matter to the early Earthhas gained much recognition. These problems are investigatedin the framework of bioastronomy.The many free parameters in the Standard Model of electroweakand strong interactions can actually be reduced to asmall number of parameters, whose values are of eminentimportance for the astrobiological development of the universe.Among these important parameters are the masses ofthe u and d quarks and their mass difference. Experimentsin elementary particle physics have established the fact thatthe mass of the u quark (≈ 5 MeV) is smaller than that ofthe d quark (≈ 10 MeV). The neutron, which has a quarkcontent udd, is therefore heavier than the proton (uud), andcan decay according ton → p + e − +¯ν e . (14.1)unstable proton?If, on the other hand, m u were larger than m d , the protonwould be heavier than the neutron, and it would decay accordingtop → n + e + + ν e . (14.2)stability of deuteriumStable elements would not exist, and there would be nochance for the development of life as we know it. On theother hand, if the d quark were much heavier than 10 MeV,deuterium (d = 2 H) would be unstable and heavy elementscould not be created. This is because the synthesis of elementsin stars starts with the fusion of hydrogen to deuterium,p + p → d + e + + ν e , (14.3)and the formation of heavier elements requires stable deuterium.Life could also not develop under these circumstances.Also the value of the lifetime of the neutron takesan important influence on primordial chemistry and thereby