At least in the past, microbes similar to today's cyanobacteria triggered an ice age (Huronian ice age or Palaeoproterozoic glaciation) that lasted almost 300 million years.

 

These microbes evolved over three billion years ago and have the special ability to produce biomass with the help of sunlight and CO2, i.e. to photosynthesise. The Earth's atmosphere at that time consisted mainly of the two greenhouse gases CO2 and methane as well as nitrogen and thus offered optimal conditions for photosynthesis. The photosynthesis of early cyanobacteria is almost identical to that of today's plants. Molecular oxygen is produced as a by-product or waste product of photosynthesis. Any oxygen present in the atmosphere comes from the activity of photosynthetic organisms such as cyanobacteria, algae and plants.

Significant oxygen concentrations arose in the atmosphere around 2.4 billion years before our time, around one billion years after the appearance of the first cyanobacteria and thus photosynthesis. The first oxygen presumably reacted with methane from the atmosphere to form CO2 and water, among other things, before it could accumulate in significant concentrations. As a result, the greenhouse gas methane disappeared and led to a serious climate change, the Huronian Ice Age.

 

Some scientists postulate that the climate change resulting from the disappearance of methane was so severe that the earth was frozen close to the equator (snowball earth). The snow-covered landscape reflected a lot of sunlight, which led to further cooling of the atmosphere and the advance of the ice masses towards the equator. Presumably, it took a period of strong volcanic activity to end the Huronian Ice Age. However, the hypothesis and the geological findings of the Snowball Earth are controversial. Regardless of climate change, the accumulation of oxygen in the atmosphere triggered one of the largest mass extinctions in the history of life on Earth to date.

Microbes also continue to influence the climate through their sheer mass. For example, microbes make up 90% of the biomass in today's oceans (phytoplankton). Photosynthetically active microbes such as cyanobacteria continue to absorb CO2 from the atmosphere. On the other hand, other bacteria and archaea that decompose plant residues in soils, for example, release large amounts of CO2. The current global warming could therefore lead to an increase in the metabolic activity of soil bacteria and thus to an increased release of CO2. Many researchers are therefore of the opinion that changes in microbial activity in permafrost soils, forests and oceans are not sufficiently taken into account in current climate models. They are therefore calling for research into microbes and their interactions with the environment to be intensified and given greater consideration in the study of climate change, as well as for the topic to be better reflected in school curricula.

 

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