Enzyme Stalled Development of Early Life on Earth for 2 Billion Years

(CN) – A special enzyme may be directly responsible for significantly slowing down the evolution of life on Earth, according to a new study published Thursday.

This is the graphic of Anabaena cylindrica, a filamentous cyanobacterium, 1946 watercolor by G.E. Fogg, FRS.

The study, published in the journal Trends in Plant Sciences, sought out to better understand the function and history of a small enzyme known as nitrogenase. The enzyme, found today only in bacteria, is largely considered to be one of the most vital biological ingredients in Earth’s oxygen production cycle, with nitrogenase making it possible for water to produce oxygen via photosynthesis. Researchers agree that without this enzyme, life on Earth would be drastically hindered.

What John Allen, co-author of the study and professor of genetics and evolution at University College London, and a team of researchers discovered, however, is that while nitrogenase may play a crucial role in Earth’s oxygen production, it may have had a previous role: slowing down the time it took for our planet to evolve by roughly 2 billion years.

Researchers suggest that nitrogenase is directly responsible for a drastic slowdown in chemical and biological evolution that took place during the Proterozoic Eon, a time commonly referred to as the “boring billion” by scientists. This is because for 2 billion years, this time period experienced remarkable few evolutionary changes as universal oxygen levels remained low.

The study reports that nitrogenase caused this slowdown by not fulfilling its core duty – that of producing oxygen – because it failed to adapt to rising atmospheric pressure. Researchers theorize that as Earth’s oxygen count began to rise, nitrogenase simply ceased to properly function, chemically chocked by the rising chemical presence of our atmosphere.

Had this not been the case, and nitrogenase adapted to the rising oxygen pressure, oxygen would have been produced at a remarkably faster rate and would have helped the planet to evolve.

“What we think we have identified in our paper is one of the pre-conditions for the establishment of an atmosphere rich in oxygen produced by photosynthesis in a biosphere,” Allen said in an email. “On Earth, photosynthesis originally created oxygen at low concentrations. If our hypothesis is correct, then oxygen rose to remotely detectable levels only when the obstacle of the oxygen-sensitivity of nitrogenase was removed by life having colonized land.”

The study suggests that this stagnation finally came to an end several hundred million years ago, when plant life began to dominate Earth’s surface. Once this took place, oxygen could be produced by the leaves of plants, and had a sizeable physical separation from the nitrogenase in the soil. This separation allowed oxygen production to drastically increase, as it was now no longer in conflict with the enzyme that for so long kept Earth’s oxygen levels stagnant.

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