Thông tin tài liệu
202 ATMOSPHERE EVOLUTION Figure Mass independent sulphur isotopic compositions track changes in atmospheric composition with time (Reproduced from Mojzsis et al (2003).) the atmosphere It has been found that sedimentary sulphide and sulphate minerals in Archaean rocks contain sulphur where the levels of the minor isotope (33S) deviate from the mass-fractionation line with other post-2.3 Ga terrestrial sulphur minerals It appears that the signal of this chemistry can be transferred from the atmosphere to surface materials and thereafter to the geological record The mass-independent fractionation effect of sulphur in ancient sulphides records chemical reactions in early anoxic terrestrial atmospheres, which were destroyed in the Early Proterozoic (2.4–2.3 Ga), and tracks the rise in levels of atmospheric oxygen (Figure 6) Metabolic Energy and the Rise of Oxygen Changes in atmospheric composition have had a profound effect on the evolution of life Sequence analyses used to compare genomes have been used to infer the phylogenetic relatedness of living organisms and their evolutionary history in terms of molecular biology and metabolic style It has been found that three great domains exist within the ribosomal RNA tree of life: Bacteria, Archaea, and Eukarya (Figure 7) (see Precambrian: Prokaryote Fossils) The organisms with the deepest branches in the tree, corresponding to the most ancient pedigrees, close to the root in Figure 7, are hyperthermophilic (heat-loving) chemoautotrophs (organisms that obtain their metabolic energy from chemical disequilibria) It appears that at least some of the earliest organisms lived off chemical energy, in much the same way as contemporary hot-spring microbial communities Such environments are widespread in volcanic centres on land and on the seafloor, and they would have been even more widespread on a geologically restive early Earth However, hyperthermophilic organisms are restricted to zones around hydrothermal vents where optimal chemical and temperature conditions persist Photosynthesizers, on the other hand, are less restricted and have evolved to inhabit environments away from those of their chemosynthetic ancestors into the open ocean Light from the Sun provides a readily accessible, stable, and inexhaustible energy source to drive metabolic reactions Photosynthesis uses light energy to capture electrons and move low-energy-state ions to higher energy states The energy released can then be used to power metabolic reactions such as growth and reproduction Photosystem I was the earliest photosynthetic pathway and used light-activated chlorophylls and electron donors such as H2S and Fe2ỵ to yield S0 and Fe3ỵ as oxidative products At a later stage, photosystem II developed; this uses water as the electron
Ngày đăng: 26/10/2022, 11:28
Xem thêm:
