New Study: Surprisingly Low Oxygen Levels Delayed Explosion Of Life
A mystery may have been solved as to why Animals didn’t flourish earlier in earth’s history even though oxygen levels should have permitted it. Scientists claim it’s because oxygen levels at that time were a fraction of what we thought they were.
Big multi-cellular life really proliferated on the earth in the period of geologic history called the Proterozoic about 800 million years ago. But the preceding billion years or so seemed to have enough oxygen for the simple organisms then existing to take advantage of. The bottom line question then has been: What the hell took so long?
A solution to this mystery may have been found according to Noah Planavsky of Yale University’s Department of Geology and Geophysics. He said:
“Our research now shows empirical evidence for a surface oxygen level that would have inhibited animal evolution”
He and his colleagues came to this conclusion after studying ancient sediments from the U.S, China, Australia, and Canada. They were specifically looking for the levels of chromium isotopes because the rate at which those isotopes oxidize (combine with oxygen) could be used to infer the amount of free oxygen in the atmosphere at the time. The stunning result is that oxygen levels before the explosion of animal life on earth were at a paltry 0.1% of what they are today. This is a far cry from previous estimates that put it at around 40%.
If these results are accurate, they could provide a direct link between atmospheric oxygen and the rise of animal life. According to Simon Poulton, a geochemist at the University of Leeds:
“If correct, the very low levels of oxygen found in this study would have provided a major restriction on early animal evolution, thus suggesting that it was indeed a rise in oxygen that ultimately stimulated the evolution of our earliest animal ancestors”
But why is oxygen so important? I know that sounds silly but couldn’t organisms use other elements or gasses in the atmosphere? It’s not like they didn’t have a lot time to come up with one. Nitrogen for example is more than three times as abundant as oxygen. The answer is that oxygen is exquisitely reactive, allowing it to liberate much more energy that could be used for metabolic activity than other elements like nitrogen. If you want to grow and have an efficient metabolism, utilizing oxygen is the way to go. It’s ironic then that 99.999% of the oxygen in our atmosphere was created by life. It’s also weird to consider that when oxygen first made the scene, it was literally a poisonous pollutant. Many species of simple organisms died out because they couldn’t deal with it. Those that could obviously took over.
Oxygen’s reactivity also means that has to be continually replenished by life otherwise it would eventually disappear from the atmosphere. This means that if or when we ever discover oxygen on an exo-planet, we can use that information to be very confident that some kind of life produced it and continues to produce it.
Before you start celebrating this low-oxygen discovery, keep in mind that there is much more work to be done to increase our confidence to sufficient levels. Professor Poulton said:
“So the problem is far from solved, but this is a major step forward and I am sure that this will spark many further studies as the record is still far from complete – this study incorporates just a few analyses across a huge period of Earth history,”
Some scientists are even more skeptical like Nicholas Butterfield of Cambridge University’s department of Earth Sciences. He claims that the researchers method of using marine rocks does not directly reflect atmospheric oxygen levels. He further believes that the long delay in animal life can be attributed to the sheer complexity of the task of evolving the necessary cellular machinery required to make that happen. After all, as he told the BBC:
“It’s the most complex recipe that evolution has ever derived.”
I can’t help thinking what our biosphere would be like if the earth had enough oxygen 2 billion years ago. The diversity and array of animal life would of course be radically different and potentially sublimely more complicated and fascinating than anything extant today.
I’m suddenly very dissatisfied with life now.
Image Credit: http://www.reasons.org/articles/an-atmosphere-without-oxygen