Complex life on Earth is generally thought to have appeared at least 1.75 billion years ago . But a young study suggests there may have been an earlier period where complex life could have evolved , before evaporate and then reappearing again .
The theory was put forward by a study led by the University of Washington , published today in theProceedings of the National Academy of Sciences . They delineate how isotopic ratios in the element Se in sedimentary rocks suggest a mellow presence of atomic number 8 in Earth ’s atmosphere between 2 and 2.4 billion age ago .
The suggestion is that for this relatively abbreviated period in Earth ’s 4.5 - billion - year history , conditions may have been lucky for complex life . Previously , it had been thought that oxygen on Earth went through a period of none , then some , then a quite a little , when eucaryote – animals , plants , kingdom Fungi , and protists – amount into existence . But this research propose there was a spike heel before “ none ” and that it dropped down again .
“ There is dodo evidence of complex cubicle that go back maybe 1.75 billion years , ” said study co - generator Roger Buick from the University of Washington in astatement . “ But the oldest fossil is not necessarily the oldest one that ever know – because the chances of getting preserved as a fogy are pretty low-down . ”
However , that ’s not to say lifetime did survive in this earlier stop . Buick added that the enquiry showed there was enough O to allow complex cells to evolve and become ecologically crucial , but that does not necessarily mean that they did .
This is n’t the first metre this hypothesis ofincreased oxygenearlier in Earth ’s chronicle has been purpose , but it does provide some additional possibility , such as Earth ’s atmosphere and surface ocean experience an gain in oxygen , but not the bass ocean .
What ’s not clear , though , is why this happened . Eva Stüeken from the University of St Andrews , another study co - author , said that was the “ million - dollar mark interrogative sentence ” .
Finding out more about this possible event could have implication for read planet outside the Solar System , too . The researcher noted that if we find oxygen in the air of a removed exoplanet , it may not necessarily suggest at a complex biosphere .
