Scientists have shown that the lengthening of the day leads to more productive photosynthesis and may have once helped cyanobacteria to carry out an oxygen revolution on the ancient Earth.
Thanks to the moon’s gravity, the speed of our planet’s rotation gradually slows down, and the day becomes about two milliseconds longer 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 that led to one of the most serious transformations in the history of life: the emergence of the oxygen atmosphere.
The major events are thought to have unfolded about 2.4 billion years ago or earlier. During that period, photosynthetic cyanobacteria emerged, releasing oxygen that dissolved into the ocean, settled into minerals, and filled the air. And, according to new work, the length of the day played an important role in this oxygen revolution. This is discussed in a new article by scientists from Germany and the United States, published in the journal Nature Geoscience.
Researchers pushed to the possible connection by bacteria living in the Middle Island Sinkhole (Middle Island Sinkhole) – a natural underwater cavern in Lake Huron in North America. 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 multilayered bacterial mats. Cyanobacteria in them neighbor and compete with sulfate-reducing bacteria, which produce energy without light, using sulfate.
Biologists have observed that sulfate-reducing bacteria move closer to the surface of the multilayer mat when it’s dark and are replaced by photosynthetic cyanobacteria when it’s light. This daily cycle is associated with microbial competition for access to the surface of the mat, where the most intense exchange of substances and energy with the environment takes place. However, the daily replacement of one bacteria by another is far from instantaneous, taking several hours.
As a result, cyanobacteria don’t have much time left for “work”. But the longer the day, the more. To test this hypothesis, scientists used data from sensors installed in the Middle Island Fault, and conducted experiments with samples of bacteria brought into the laboratory. On this basis, a model was derived that showed the dependence of oxygen release on the frequency of light and dark periods.
It would seem that two 12-hour days are the same as one 24-hour day; however, in terms 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 mean that cyanobacteria need considerable time to “fire up” and launch these processes to their full potential. Therefore, lengthening the daylight hours can dramatically increase their efficiency – which is apparently what happened in the era of the oxygen revolution.