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Phosphorus and the Oxygen Connection

In deep geologic time, it may have helped turned the sky from orange (!) to blue, a new study shows.

As recently reported by Miller-McCune, scientists believe the world may be approaching "peak phosphorus." Supplies of phosphate rock, a key source of phosphorus for fertilizers, may start to decline in 20 years, they say, triggering famine and food shortages.

Now, beyond food, phosphorus is getting credit for the very air we breathe. New research from the Carnegie Institution for Science suggests that hundreds of millions of years ago, phosphorus may have jump-started the modern-day atmosphere, paving the way for the evolution of complex life forms and even turning the sky blue.

Biochemist Dominic Papineau studied the phosphate deposits that formed during a critical interval in the history of the Earth, from 2.5 billion years ago to about 540 million years ago. During this period, levels of oxygen in the atmosphere increased in two phases, from trace amounts to near-present levels, giving rise to a spectacular explosion in the diversity of life forms, including sponges and hard-shelled marine organisms.

"Phosphate rocks formed only sporadically during geologic history," Papineau was quoted in a release announcing his paper, "and it's striking that their occurrences coincided with major global biogeochemical changes as well as significant leaps in biological evolution."

Over geologic timescales of tens of millions to a few hundreds of millions of years, he said, supercontinents broke up and glaciers melted, increasing the weathering of the Earth's crust and washing large quantities of phosphorus into the oceans.

"When you melt a 'Snowball Earth,' you're going to create a lot of rivers," Papineau told "That has the potential to erode the crust under the ice sheet and make rivers all over the place. That will really accelerate the erosion and lead to higher rates of delivery of phosphorus to the ocean."

Once there, he said, the phosphorus likely fed the growth of vast blooms of cyanobacteria, or blue-green algae, which in turn pumped oxygen into the atmosphere.

"The previous atmosphere was possibly methane-rich, which would have given the sky an orangish color," Papineau was quoted. "So this is the time that the sky literally began to become blue."

During Great Oxidation Event, when the oxygen in the atmosphere increased to 10 percent of present-day values, single-celled organisms grew large and acquired cell structures called mitochondria, the so-called "powerhouses" of cells. Mitochondria burn oxygen to yield energy. In the second phase studied by Papineau, ending 540 million years ago, oxygen increased to near-present levels, climaxing in the most significant leap in biological diversity and complexity in Earth's history. The "Cambrian Explosion," as it is called, has been documented in the fossil record.

"Phosphorus has been overlooked," Papineau told "I think it's an essential clue. Phosphate is one of the main connections between the geosphere, the crust and the weathering — and the biosphere, the cyanobacteria and all the changes they cause when they bloom."