The Rise of Oxygen and the origin of the Eukaryotic Cell
Oxygenic photosynthesis started out locally, but its considerable advantage over organisms requiring externally produced food molecules resulted in its global expansion. The need for carbon dioxide might initially have been met by such CO2 as was contained in the atmosphere and dissolved in the oceans. When this was consumed, all photosynthesizers had to depend on new CO2 produced by geologic process, such as subduction of organic sediments followed by reaction of reduced carbon compounds in the sediment with water under magmatic conditions in the upper mantle of Earth. This supply of new carbon dioxide lasted for a billion years or more, and in fact is still producing some CO2 at present, though probably not in amounts comparable to the early Precambrian. Oxygenic photosynthesis opened up an enormous new energy supply for life. In parallel with this, oxidative metabolism using available molecular oxygen resulted in much more efficient cells. These could be larger since nutrient supply to the interior parts of the cells was now more efficient. The increase in cell size may have made it possible for cells to isolate their DNA into separate compartments (nuclei) in which the DNA would be more protected from the surroundings, and thus a more stable and reliable storage vehicle for genetic information. More stable genomes could also become larger, perhaps yielding more complex cells. Eukaryote cells, with numerous intracellular bodies doing specialized work in the cell, may have arisen by capture of smaller prokaryotic cells by the larger, possibly nucleated cells. These more sophisticated cells were able to thrive using the contributions of their internal partners, such as mitchondria and chloroplasts, and eventually became the basis for multicellular organisms.
KeywordsPlate tectonics Subduction Magma/magmatism Mitochondria Chloroplast Eukaryote/eukaryotic Nucleus ATP Cyanobacteria
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