![]() ![]() Thus, Mulkidjanian and his colleagues argue that they may have been the "hatcheries" of the first cells. Condensed geothermal steam in these pools can have ratios of potassium to sodium ions as high as 75 to 1, and are rich in the other elements of life that have been leached from rock by the hot water. The only such places extant today are so-called "vapor-dominated" geothermal systems-locales where water, heated deep within Earth until it becomes steam, reaches the surface, cools and condenses back to elementally enriched liquid pools. "We looked all over the place for the conditions and processes that would lead to enrichment," Mulkidjanian says. The team noted that most modern cells maintain a high ratio of potassium ions to sodium ions. "By reconstructing the inorganic chemistry of the cytoplasm, it might be possible to reconstruct the habitats where the first cells could dwell." "If the very first membranes were leaky for small molecules and ions, then the interior of the first cells should have been in equilibrium with their surroundings," explains biophysicist Armen Mulkidjanian of the University of Osnabrück in Germany, lead author of the paper presenting the hypothesis published online February 13 in Proceedings of the National Academy of Sciences. That modern archaea and bacteria instead possess internal fluid low in sodium, and enzymes built from other elements hints that they arose in an environment both rich in such elements as well as relatively sodium-free. If life arose in the salty sea, then the first cells and their living relatives might be expected to have enzymes built from abundant sodium-or at least tolerate more sodium internally. Some biologists suspect that the membranes of early life-forms were not yet the tight coverings that they are today, and would have instead let small molecules and ions flow in and out freely. ![]() The argument rests on one indisputable observation-enzymes common to all archaea and bacteria are built from potassium, phosphorus or zinc, not sodium. But a new study suggests that the first cells-or at least the ones that left descendants still extant-got their start in geothermal pools, like those seen at Yellowstone National Park and other geologic hot spots today. Given these inhospitable conditions, scientists have long wondered: How did the first cells come to be nearly four billion years ago?Ĭonventional scientific wisdom holds that life arose in the sea. Furthermore, the thin primeval atmosphere may have provided only scant protection from the young sun's harsh ultraviolet glare. Earth started as a violent place, its surface churned by continuous volcanic eruptions and cloaked in an atmosphere that would have been poisonous to today's life-forms. ![]()
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