The first animals may have caused global warming and anoxia in the oceans


An article published in the journal “Nature Communications” describes a research on the consequences of the evolution of the first animals on the Earth’s climate over 500 million years ago. A team of researchers investigated the consequences of the process called bioturbation, the reworking of soil and sediment by animals or plants, the cycles of phosphorus, oxygen and sulfur concluding that it led to a drop in oxygen in the seas and a global warming with various mass extinctions over the next 100 million years.

The scarcity of fossils doesn’t allow to establish with certainty when the first animals evolved in the Paleozoic era’s Earth seas but about 540 million years ago there was the so-called Cambrian explosion with the greatest diversification of species ever seen in history of life on the planet. The sea floor was filled with creatures that ate the organic materials present and dug burrows, although at a depth limited that could go from 1 to 3 centimeters.

There’s a branch of paleontology and geology called ichnology that specifically studies the traces such as planolites (photo ©FunkMonk) left by animals, called ichnofossils. These traces allow among other things to reconstruct the bioturbations that occurred in the past, even those of the Cambrian period studied in this research. An article published in September 2017 in the journal “Nature” described the study of tiny traces left by organisms in that period.

All this may seem irrelevant as far as the climate is concerned, instead it could have had profound consequences. Those animals’ growing activity transformed the sea floors and led to an increase in global consumption of oxygen and carbon dioxide emissions. In the Cambrian seas, this led to a growing anoxia, meaning a presence of no oxygen or almost no oxygen dissolved in the waters.

In the atmosphere, the growth of carbon dioxide slowly caused global warming. In essence, animals that had little activity had a strong global influence over the long term. Previous research had already indicated those phenomena during about 100 million years after the beginning of the Cambrian explosion but now the authors of this new research believe they have found their causes in the first animals.

The consequences of those phenomena with the extinction of a large amount of species over a long period were already known. This new research may have found the culprits in the first animals in a disturbing parallel with what’s happening today. Traces of past events of anoxia in the oceans are typically linked to mass extinctions and today the oceans are again affected by that problem.

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