Could Earth’s mantle control the rise of oxygen?This photo shows peat – high organic carbon material

Could Earth’s mantle control the rise of oxygen?This photo shows peat – high organic carbon material formed today out of plant matter. Every bit of organic carbon on Earth, including the stuff I’m using to type on this keyboard, at some point started out as carbon in the atmosphere. Organic carbon is produced when organisms take CO2 from the atmosphere or ocean, break it apart using energy, and turn it into carbon while releasing oxygen. The first life forms on Earth had to do this process using chemical energy, but about 3 billion years ago life figured out how to use sunlight as the source of energy that drove this reaction. Single-celled organisms began creating carbon by photosynthesis, releasing oxygen to the atmosphere in the process. By 2.5 billion years ago, oxygen became a regular constituent in the atmosphere, but even though life forms were releasing oxygen, the abundance of that gas didn’t rise anywhere close to the level seen today for nearly 2 billion years. All the ingredients seem to be there, but there just wasn’t enough carbon being buried to push oxygen up in the atmosphere. Why?A new paper proposes that one possible explanation for why oxygen did not rise in the atmosphere is actually found in the mantle, and connected to the surface through the element phosphorus.Phosphorus poorly fits in the mantle, it is what we call an incompatible element. When the mantle melts, phosphorus is concentrated into the magma, and eventually it is concentrated in the Earth’s crust. However, when Earth first formed, the planet was so hot that any phosphorus in early magmas was going to be diluted by everything else that melted. Early rocks, therefore, have less phosphorus in them than more recent rocks.Phosphorus is a nutrient element required for life to flourish. There are areas of the planet today that are phosphorus-limited, meaning that more organisms could live there if there was more phosphorus available, they have every other nutrient they need in abundance.This paper, led by researchers from The University of Adelaide, suggests that these two topics are connected. Over time, as the planet cools off, phosphorus will go up in rocks coming out of the mantle. As these rocks get more phosphorus in them due to the planet cooling, weathering them releases more phosphorus out to the world, and more organisms are able to grow.More organisms able to grow means forming more biomass, and more biomass means more oxygen in the atmosphere. Basically, increase the phosphorus in rocks, life gets more phosphorus, more life grows, and the end result is more oxygen in the atmosphere.There are complications to this idea, of course. As the continental crust was forming, erosion on continents could trap phosphorus in long-lived sedimentary rocks, removing it from the nutrient cycle, and these authors consider some cases where that may have happened during the Precambrian when oxygen contents still remained low.If this hypothesis is an important one for evolution of the ecosystem on Earth, it will also be important on any other body where life exists. Phosphorus will have the same behavior elsewhere, and if it is a common key nutrient element as is found on Earth, then large planets that remain hot for long periods of time, or planets that do not cool efficiently through plate tectonics, may have a limit to how large of a biosphere they could develop. Oxygen may be easier to detect in the atmosphere of planets like ours – ones that efficiently bring nutrients to the surface and concentrate them through plate tectonics.-JBBImage credit: Public Domain Pictureshttps://bit.ly/2N3jXUzOriginal paper:https://bit.ly/2tv1xn8 -- source link

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