Sprecher
Beschreibung
After 70 years of experimentation, we still have not reconstructed the origin of life – but in the meantime many interesting experiments have been conducted, some more promising than others. One of the constraints may be that the topic is approached from too much of an organic chemistry point of view and not enough from the environmental side. Happily, there is budding awareness of the importance of environmental conditions during the Hadean, when life emerged on Earth. But the danger lies in the desire of chemists to constrain their experiments to their own idea of Hadean conditions – because their experiments work better if there is some control.
Life emerged as a natural evolution of chemistry into biology more than 4 billion years ago on a world that was totally different to the Earth today. Origins of life researchers suggest life emerging in submarine hydrothermal vents and their environments, in pumice rafts, in subaerial lakes fuelled by radioactive energy sources, in rivers or ponds, or in subaerial hydrothermal systems. The difficulty is establishing the local-scale conditions that fomented prebiotic chemistry 4 billion years ago. Much can be learned from the ancient rock record but there are limitations. The oldest, well-preserved rocks formed 1 billion years after the consolidation of the Earth. Rare older rocks are highly altered. Piecing together the local environments of Hadean Earth from the rock record is challenging.
It is certain that the different environments evoked for the emergence of life generally have compelling attributes (pumice rafts, however, are not very plausible, nor is the idea of uranium-rich placer sands, since U only became significantly mobile after the Great Oxygenation Event at ~2.4 Ga). It is likely that some degree of molecular evolution took place in most of them. The question is, to what extent? Simply the formation of complex molecules or did living cells emerge? Did life emerge in more than one environment? Would it have been possible for a variety of interesting molecules formed in subaerial to subaqueous environments to mix in the “middle ground, i.e. at the edges of shallow marine basins with hydrothermal activity?
Another question concerns the emergence of extraterrestrial life. If life emerged in one environment on Earth, let us say on emerged landmasses, could it have emerged in a purely subaqueous environment on another planetary body, such as the icy moons Europa and Enceladus? We need open minds to consider dirty chemistry in realistic, and possibly different, geological environments.
