Cambrian Explosion: role of phosphorus (Introduction)

by David Turell , Thursday, December 22, 2016, 01:16 (2675 days ago) @ David Turell

Phosphorus is a major element in the molecules of life. It had to accumulate along with oxygen for multicellular life to explode:

http://phys.org/news/2016-12-billion-years-earth-history-fertilizer.html

"Then came a fierce planetary metamorphosis. Roughly 800 million years ago, in the late Proterozoic Eon, phosphorus, a chemical element essential to all life, began to accumulate in shallow ocean zones near coastlines widely considered to be the birthplace of animals and other complex organisms, according to a new study.

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"'The most basic change was from very limited phosphorous availability to much higher phosphorus availability in surface waters of the ocean," Reinhard said. "And the transition seemed to occur right around the time that there were very large changes in ocean-atmosphere oxygen levels and just before the emergence of animals."

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"The path to understanding how a nutrient dearth would starve out breathable oxygen production leads back to a very special kind of bacteria called cyanobacteria, the mother of oxygen on Earth.

"'The only reason we have a well-oxygenated planet we can live on is because of oxygenic photosynthesis," Planavsky said. "O2 is the waste product of photosynthesizing cells, like cyanobacteria, combining CO2 and water to build sugars."
And photosynthesis is an evolutionary singularity, meaning it only evolved once in Earth's history - in cyanobacteria.

"Some other biological phenomena evolved repeatedly in dozens or hundreds of unrelated incidences across the ages, such as the transition from single-celled organisms to rudimentary multicellular organisms. But scientists are confident that oxygenic photosynthesis evolved only this one time in Earth's history, only in cyanobacteria, and all plants and other beings on Earth that photosynthesize coopted the development.

"Cyanobacteria are credited with filling Earth's atmosphere with O2, and they've been around for 2.5 billion years or more.

"That begs the question: What took so long? Basic nutrients that fed the bacteria weren't readily available, the scientist hypothesize. The phosphorus, which Planavsky and Reinhard specifically tracked, was in the ocean for billions of years, too, but it was tied up in the wrong places.

"For eons, the mineral iron, which once saturated oceans, likely bonded with phosphorous, and sank it down to dark ocean depths, far away from those shallows—also called continental margins—where cyanobacteria would have needed it to thrive and make oxygen. Even today, iron is used to treat waters polluted with fertilizer to remove phosphorous by sinking it as deep sediment.

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"something did change about 800 million years ago, and cyanobacteria and other minute organisms in continental margin ecosystems got more phosphorus, the backbone of DNA and RNA, and a main actor in cell metabolism. The bacteria became more active, reproduced more quickly, ate lots more phosphorus and made loads more O2.

"'Phosphorus is not only essential for life," Planavsky said. "What's implicit in all this is: It can control the amount of life on our planet."

"When the newly multiplied bacteria died, they fell to the floor of those ocean shallows, stacking up layer by layer to decay and enrich the mud with phosphorus. The mud eventually compressed to stone.

"As the biomass increased in phosphorus content, the more of it landed in layers of sedimentary rock," Reinhard said. "To scientists, that shale is the pages of the sea floor's history book."
Scientists have thumbed through them for decades, compiling data. Planavsky and Reinhard analyzed some 15,000 rock records for their study.

"The first compilation we had of this was only 600 samples," Planavsky said. Reinhard added, "But you could already see it then. The phosphorus jolt was as clear as day. And as the database grew in size, the phenomenon became more entrenched."

"That first signal of phosphorus in Earth's coast shallows pops up in the shale record like a shot from a starting pistol in the race for abundant life."

Comment: Now we can add phosphorus to the necessary triggers for the Cambrian explosion. But there had to be a drive to evolve within the early simple life for living organisms to react with such complexity seen in the Cambrian, which lacks any true precursors. Darwin's fears of the Silurian have been realized.