A deficiency of oxygen and the heavy metal molybdenum in the ancient deep ocean may have delayed the evolution of animal life on Earth for nearly two billion years. ‘For decades it was assumed that the ocean became oxygenated shortly after an initial rise in atmospheric oxygen about 2.4 billion years ago,’ said Dr Poulton. ‘This study provides independent confirmation that there was a major delay in the oxygenation of the ocean, and furthermore, it now appears that the availability of molybdenum may have played a crucial role in animal evolution.
‘At last, a coherent picture of the environmental conditions that led to the evolution of animal life is emerging.’
Past research has shown that Earth’s oxygenation occurred in two major steps: The first step, around 2.4 billion years ago, took place as the ocean transformed to a state where only the surface ocean was oxygenated by photosynthesizing bacteria, while the deep ocean was relatively oxygen-free.
The second step, around 600 million years ago, marked the point when the entire ocean became fully oxygenated through a process not yet fully understood. The purpose of this research was to find out the state of the ocean between the two steps.
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Maybe it's just me but the more we learn about life on Earth, the more it seems that the transition from 'simple' reproducing entities to complex, multicellular motile life forms larger than a centimeter or so is not a straightforward process. Given the relatively begnin and stable environment of this well situated water planet around a stable non-flare star of long lifetime it's sobering how many billions of years it took to invent a frog.