Scientists have shown that lengthening the day leads to more productive photosynthesis and may have once helped cyanobacteria make the oxygen revolution on ancient Earth.
Thanks to the gravity of the Moon, the speed of rotation of our planet is gradually slowing down, and the day becomes longer by about two milliseconds per century. On the scale of human life, these changes are imperceptible, but, accumulating over millions of years, they have a huge impact on the entire biosphere. Perhaps it was they who led to one of the most serious transformations in the history of life - the emergence of an oxygen atmosphere.
It is believed that the main events developed about 2.4 billion years ago or earlier. At that time, photosynthetic cyanobacteria appeared, releasing oxygen, which dissolved in the ocean, settled in mineral compounds, and filled the air. And, judging by the data of the new work, the length of the day played an important role in this oxygen revolution. This is described in a new article by scientists from Germany and the United States, published in the journal Nature Geoscience.
A possible connection was prompted by bacteria living in the Middle Island Sinkhole, a natural underwater cavern on Lake Huron in North America. The conditions there are extreme: the water is saturated with sulfur and poor in oxygen. However, the rocks are covered with thriving communities of extremophile microbes that form multi-layered bacterial mats. Cyanobacteria in them coexist and compete with sulfate-reducing bacteria, which generate energy without light, using sulfate.
Biologists have noticed that in the dark, sulfate reducers rise closer to the surface of the multilayer mat, and in light, they are replaced by photosynthetic cyanobacteria. This daily cycle is associated with the competition of microbes for access to the surface of the mat, where the most intensive exchange of substances and energy with the environment takes place. However, the daily change of some bacteria to others does not occur instantly, taking several hours.
As a result, cyanobacteria do not have much time to “work”. But the longer the day, the more it is. To test this hypothesis, scientists used data from sensors installed in the Middle Island dip, and also conducted experiments with bacteria samples brought to the laboratory. On this basis, a model was obtained that showed the dependence of oxygen evolution on the frequency of alternation of light and dark periods.
It would seem that two days for 12 hours is the same as one day in 24 hours; however, from the point of view of photosynthesis, they are far from equal. The limitations associated with the slow movement of microbes and the diffusion of molecules through the bacterial mat lead to the fact that cyanobacteria take a noticeable time to "heat up" and start these processes in full force. Therefore, the lengthening of daylight hours can dramatically increase the efficiency of their work - which, apparently, happened in the era of the oxygen revolution.