Natures wonders: early nitrogen cycle mechanism (Introduction)

by David Turell , Friday, June 29, 2018, 20:31 (2337 days ago) @ David Turell

Where did the early Earth's nitrogen in the atmosphere come from? New study proposals:

https://phys.org/news/2018-06-continental-microbes-seed-ancient-seas.html

"Now, ASU researcher Ferran Garcia-Pichel, along with Christophe Thomazo, from the Laboratoire Biogéosciences in Dijon, France, and Estelle Couradeau, a former Marie Curie Postdoc in both labs, show that biological soil crusts—colonies of microorganisms that today colonize arid, desert environments—may have played a significant role in the Earth's nitrogen cycle, helping to fertilize early oceans and create a nutrient link between atmosphere, continents and oceans.

"Garcia-Pichel directs the Biodesign Center for Fundamental and Applied Microbiomics and is a professor in ASU's School of Life Sciences. Originally, a marine microbiologist, he became fascinated with the hidden world of microorganisms that lay on top of soils in deserts and other arid regions devoid of plant life. These living biocrusts have remarkable properties, thriving in extreme conditions, helping to anchor soils in place, so they resist erosion, and fertilizing rangelands and deserts.

"The new research, which appears in the advanced online edition of the journal Nature Communications, suggests that analogs of these biocrusts spread across otherwise desolate continents of the early Earth, and contributed to establishing the nitrogen cycle essential for life as we know it today.

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"Today, nitrogen makes up 78 percent of the atmosphere. It is a vital element in DNA, RNA and proteins, the key components of life. But the nitrogen found in the atmosphere is not suitable for use by most organisms. It must first be processed, through what is known as the nitrogen cycle. This occurs when prokaryotic organisms carry out nitrogen fixation, making atmospheric nitrogen available in a form useful to plants and animals for survival.

"While it has long been assumed that the nitrogen cycle that arose early in the Earth's history, resulted from oceanic microbes during an ancient phase known as the Archean, new research suggests significant amounts of nitrogen came from land-based biological soil crusts.

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"...intricate microbial communities similar to biocrusts found in present-day desert environments, colonized the early continents. Traces of their presence date to 3.2 billion years ago, well before the Great Oxygenation Event helped set the stage for the Cambrian explosion—a sudden burst of life that gave rise to most of the world's animal phyla.

"The researchers note that today, such biocrusts occupy roughly 12 percent of the Earth's land. They are composed of filamentous cyanobacteria, which perform most of the biocrust's carbon and nitrogen fixation and provide nutrients to the rest of the crust microbiome, while bonding soil grains together and providing microbial communities with erosion resistance.

"'These communities live on light," Garcia-Pichel says. "When plants evolved and started to accumulate, this marked their demise. There's no light on the soil anymore because of plant litter accumulation". However, in an early world, before the evolution of plants, there would be nothing to impede their colonization of the continents, where conditions for their growth and development would have been considerably less harsh.

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"Quantitative analysis suggests that biocrust contribution to nitrogen cycling during the early history of the Earth would have been significant, even with limited colonization of the pre-Cambrian continents.

"The notion of land-based life forms—the biocrusts—providing a significant contribution to the Earth's early biogeochemistry represents a significant paradigm shift. New research should help establish just how far back in Earth's record these microbial biocrusts extend and help explore their contributions to the cycling of other elements, like phosphorus."

Comment: Starting with a rocky planet without carbon-based molecules useful for life, many necessary systems had to be developed. Note that fortunately cyanobacteria arrived at the right time. More evidence of design.