Privileged Planet:Earth itself helped get high oxygen levels (Introduction)

by David Turell , Tuesday, December 10, 2019, 21:51 (1609 days ago) @ David Turell
edited by David Turell, Tuesday, December 10, 2019, 22:00

A new study thinks it was mainly the photosynthetic bugs encouraged by what was available on Earth:

https://www.newscientist.com/article/2226874-why-is-earth-so-rich-in-oxygen-the-answer-...

"It may have been unexpectedly easy for the air to become rich in oxygen. A new simulation of the rise of oxygen suggests it was driven by the planet itself, and needed little help from living organisms.

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"Oxygen levels then rose twice more: once between 800 and 540 million years ago, and again 450-400 million years ago.

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"Scientists have tried to explain the oxidation events by linking them to major evolutionary shifts or tectonic activity, says Simon Poulton of the University of Leeds. For instance, the final rise has been linked to the spread of land plants.

"Alcott and Poulton believe there is no need to invoke any such dramatic events, other than the initial evolution of photosynthetic bacteria. With Benjamin Mills, they have shown that the behaviour of the planet is enough to explain the stepwise rises in oxygen levels.

"The key is that Earth’s mantle has been gradually cooling since the planet formed, and as it cools it releases fewer volcanic gases like sulphur dioxide, which react with oxygen and remove it from the air. When the team modelled how this shift affected the cycling of oxygen around the planet, they observed three sharp increases in oxygen that corresponded to the known oxidation events.

"The initial Great Oxidation Event came about because the oxygen from bacteria overwhelmed the volcanic gases in the air. Levels then held steady for millions of years, because any extra oxygen reacted with minerals on land.

"In the model, the second rise happened because the extra oxygen changed the nature of phosphorus-containing materials, making them more likely to be buried in sediments. Phosphorus is a vital nutrient, so this change meant fewer organisms that would otherwise have taken in oxygen, allowing more oxygen to escape into the air and into surface layers of the sea. The same process led to a third sharp rise in oxygen, when it reached the deep ocean."

Comment: Studies continue to show how this planet prepared for life to start. Planned by God!? Another site explains the research done:

https://phys.org/news/2019-12-life-oxygen-debate.html

"In a new study, Leeds researchers modified a well-established conceptual model of marine biogeochemistry so that it could be run over the whole of Earth history, and found that it produced the three oxygenation events all by itself.

Their findings suggest that beyond early photosynthetic microbes and the initiation of plate tectonics—both of which were established by around three billion years ago—it was simply a matter of time before oxygen would reach the necessary level to support complex life.

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"The first "Great Oxidation Event" occurred during the Paleoproterozoic era—roughly 2.4 billion years ago. The subsequent wholesale oxygenation events occurred in the Neoproterozoic era around 800 million years ago and finally in the Paleozoic Era roughly 450 million years ago, when atmospheric oxygen rose to present day levels.

"Large animals with high energy demands require high levels of oxygen, and evolved soon after the last of these steps, ultimately evolving into dinosaurs and mammals.

"Currently, the two prevailing theories suggest the drivers of these oxygenation events were either major steps in biological revolutions—where the evolution of progressively more complex lifeforms essentially "bioengineered" oxygenation to higher levels—or tectonic revolutions—where oxygen rose due to shifts in the style of volcanism or make-up of the crust."

Comment: Clarifies the concepts. Lots of oxygen allows for evolutionary advances as genomes are changed.