A mass extinction is a colossal event that is accompanied by easily recognizable phenomena and events. Experts believe that one of these markers of an impending disaster in the distant past was a sharp increase in the number of microorganisms in lakes and rivers.
Wildfires, abnormal heat and abundant "blooming" of reservoirs - researchers are noticing more and more signs indicating the proximity of another mass extinction.
So, for example, after the Permian extinction, which happened 252 million years ago, there was a sharp surge in bacterial and algal blooms, which lasted hundreds of thousands of years. According to research by geologists, the devastating consequences of abrupt climate change and massive deforestation have led to the fact that the Sydney Basin - one of the oldest freshwater ecosystems on Earth - has turned into a "poisonous broth" of phytoplankton and other organisms.
Why is it so important? Recently, massive fires due to an abnormally hot summer have destroyed large tracts of forest in Australia. Ash blown into the ocean by the wind contains a lot of iron and organic particles. As a result, it acted as a catalyst that accelerated the reproduction of phytoplankton - now a significant part of the ocean has become poisonous due to the abundance of "blooming" microbes.
An unpleasant coincidence, isn't it? Alas, it is far from the only one. Geologist Tracy Frank of the University of Connecticut notes that “… in the past, the source of CO2 was volcanic activity. However, we calculated that the rate of entry of carbon dioxide into the atmosphere then and now is almost the same, only in the 21st century human activity becomes its source."
Algae and bacteria are the most common elements of the freshwater environment, but their uncontrolled proliferation literally sucks oxygen out of the water, creating zones of "dead water" in which larger creatures cannot survive. Global warming, deforestation and the leaching of nutrients from the soil into the water are three factors that contribute to this harmful phenomenon.
After examining data from soil and geochemical analysis of the Sydney Basin, the researchers conclude that the spread of microbes after the Permian extinction "was both a symptom of the collapse of the continental ecosystem and the reason for its slow recovery."
Volcanic eruptions initially caused an accelerated and sustained rise in greenhouse gas emissions. This, in turn, triggered an increase in global temperatures on the planet and its sudden deforestation due to wildfires and droughts.
As soon as the trees disappeared, the soil structure began to deteriorate, and nutrients entered the freshwater ecosystems. For more than three million years, Earth's forests have fought to recover. Instead, the Sydney Basin was littered with low-lying ecosystems that "were regularly inundated with stagnant fresh and brackish bodies of water that were home to thriving populations of algae and bacteria," the authors write.
In turn, these persistent dead zones have impeded the recovery of important carbon sinks such as peatlands and slowed down the recovery of climate and ecosystems.
Other studies around the world also show that microbial blooms are common after mass extinctions caused by warming. The exception seems to be the case of an oversized asteroid that caused the extinction of the dinosaurs 66 million years ago.
This episode lifted huge amounts of dust and sulfate aerosols into the atmosphere, but compared to volcanic activity, the meteorite caused only a moderate, rather than sustained, increase in carbon dioxide concentration and temperature. Thus, the outbreak of microbial bloom was short-lived.
Alas, all these apocalyptic omens are not very different from the picture of our day. For example, the researchers note that the “optimal temperature range for growth” of harmful microalgae in freshwater environments is 20-32 ° C. This range corresponds to the calculated continental summer surface air temperatures for the region in the Early Triassic. And this is precisely the range predicted for mid-latitude summer surface air temperatures by 2100.
What's in store for us? Only time will tell. But one thing is already clear today: if urgent and extraordinary measures are not taken by the efforts of the entire planet to reduce the level of pollution of the planet, then we will not need to wait a century to see the harmful consequences of man's negligence towards the Earth.