Varying arsenic concentrations in the oceans lead to the fall and rise of atmospheric oxygen.
A team of researchers has revealed that the rapid evolution of complex life was hampered by the ocean toxicity. By examining rocks at the bottom of ancient oceans, the Stockholm University team found that arsenic concentrations in the oceans have varied greatly over time, but also, that in the very early oceans, arsenic co-varied with the rise of atmospheric oxygen and coincided with the coming and going of global glaciations.
Team leader Ernest Chi Fru said that in the article, the researchers argue that when they first see the appearance of complex life on Earth, is when life have developed mechanisms to resist catastrophic chemical changes forced by global glaciations and that, this enabled the expansion of complex life in oceans and paved the way for our own evolution.
Oxygen first appeared in the atmosphere when marine arsenic concentrations were quite low, which was after 2.45 billion years ago, according to the researchers. Around this time, the earth had its first global glaciation. When these glaciations ended, there was an increase in marine arsenic concentrations, which resulted in a reduction of atmospheric oxygen.
The authors infer from the way modern photosynthetic organisms react to changing marine arsenic concentrations that this event was due to widespread ocean toxicity resulting from the release of toxic elements into the oceans when the ice melted.
A similar low and high arsenic content accompanied the coming and going of global glaciations at around 0.7 billion years ago, which is when Earth first saw the appearance of complex life. While the low marine arsenic concentrations again coincide with a rapid rise in atmospheric oxygen content to near modern day levels at this time, the subsequent increase when the ice melted is not accompanied by atmospheric oxygen decline.
The study is published in the Nature Group Journal, Scientific Reports.
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 "Stockholm University, oceanic, toxicity, arsenic, oxygen, evolution, Ernest Chi Fru")
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