Why did the earth warm three billion years ago, when the young sun was still shining so weak? Researchers can now find an explanation for this paradox: Microbes in the iron-rich oceans at that time release densely the greenhouse gas methane into the atmosphere, causing temperatures to rise. Research results from a lake in Indonesia support this scenario, where conditions are basically similar to those of the sea three billion years ago. Analysis shows that the microbes release very large amounts of methane there.
This is known as the “weak young sun paradox”: because of our still low stellar radiation, most of Earth’s oceans should have frozen three billion years ago. But geological evidence shows that is not the case. This contradiction actually emerged in the 1970’s. A possible explanation is that the strong greenhouse effect must be responsible for warming the Earth’s atmosphere at that time. But how such high concentrations of greenhouse gases came into being is a mystery.
What warmed the earth three billion years ago?
The conditions of the oceans at that time seemed to oppose the massive production of methane, which was extremely potent from greenhouse gases by the microorganisms already present at the time. Because there is almost no free oxygen and the sediments are mostly made up of ferrous minerals. Today this is evidenced by so-called iron ore deposits – the most important iron ore deposits on Earth. Given these biochemical conditions, metabolic processes will most likely produce carbon dioxide, which, compared to methane, has a much less greenhouse effect.
In order to obtain more accurate information about microbial processes such as those that took place in the oceans three billion years ago, an international research team has now devoted itself to investigating a body of water with unusual conditions: Lake Tutti in the forests of Sulawesi Island is located at a depth of more than 130 meters. From oxygen-free water rich in dissolved iron. Iron minerals, especially iron oxides, make up more than one-third of the sedimentary material. The researchers explain that conditions in Lake Tutti are very similar to those of the ocean about three billion years ago. For their investigation, they extracted samples of sediment holes from the depths of the lake. Samples were taken from them, which were then sent to the participating research group’s laboratories. Then scientists there carried out mineralogical and biochemical studies of microbial metabolism.
Methane production is staggering
As the researchers explain, they have predicted that in the absence of oxygen, the microbes will primarily use the iron oxide in the sediments to process organic matter, resulting in the release of carbon dioxide in the process. In fact, they found that the organisms in the Lake Tutti sediments instead used a metabolic process to produce methane. “Because microorganisms prefer to use the mineral oxide mineral in laboratory studies, this research has thus far provided the basis for our knowledge of such metabolism on Earth from an early age,” said first author Kohen Bauer of the University of British Columbia in Vancouver. “However, our findings from Lake Tutti are now forcing us to rethink the processes that contributed to Earth’s early climate regulation.”
As the researchers explain, the methane rising from the sediments of Lake Tutti is now rapidly converting to carbon dioxide by reaction with dissolved oxygen in the upper water layer. However, due to a lack of oxygen three billion years ago, this process did not exist so that the gas could be transported into the atmosphere in large quantities. Because methane is a much more potent greenhouse gas than carbon dioxide, this fertilization process warmed the world’s climate at that time, scientists say.
“Our results from Lake Tutti challenge current knowledge of microbial processes in iron-rich environments. The results were very different from what was expected. That way, we can help solve the mystery of the evolution of the atmosphere three billion years ago, “said senior author Jens Kalmer of the Potsdam German Center for Geoscience Research. “Due to its special chemical properties, we see Lake Tutti as the perfect model system for now. However, we are only slowly starting to understand its properties. ” Now microbiologists hope to gain more interesting insights from this mysterious body of water deep in the forests of Sulawesi Island.
Source: Helmholtz Center Potsdam – GFZ German Research Center for Geosciences. Technical Articles: Nature Communications, doi: 10.1038 / s41467-021-22453-0
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