How a Microbial Evolutionary Accident Changed Earth’s Atmosphere

A dense rainforest or other verdant terrestrial vegetation may be what first comes to mind at the mention of photosynthesis. Yet the clouds of phytoplankton that fill the oceans are the major drivers of that process in nature. The plantlike single-celled aquatic microbes generate more than 50 percent of the oxygen in the atmosphere, and they absorb nearly half of the carbon dioxide, converting it into the glucose, fats, proteins and other organic molecules that nourish the food web of the oceans.

A recently published study in Current Biology finally pins down the source of this unparalleled photosynthetic efficiency, which has long baffled scientists. The new research found that some phytoplankton are equipped with an extra internal membrane that carries a “proton pump” enzyme that supercharges their ability to convert carbon dioxide into other substances. The enhancements due to this one protein modification seem to contribute to the production of nearly 12 percent of the oxygen in the air and as much as 25 percent of all the carbon “fixed” (locked into organic compounds)…