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The extreme oxygen fluctuations in the atmosphere corresponded to phases of expansion or decline of biodiversity in the Cambrian, between 540 and 485 million years ago: it was perhaps precisely the quantity of this gas that triggered the massive diversification of species that characterized the Earth starting from from 540 million years ago and for about 20 million years, as well as to determine some extinction events that occurred before and after that phase.

According to a study by University College London and the University of Leeds published in Nature Geoscience, which sheds light on the trigger of the Cambrian life explosion, a fundamental phase of life on our planet, in which suddenly and in an arc of short time on the geological time scale the forerunners of the animals that populated the Earth were born.

In the Cambrian, atmospheric oxygen fluctuations have affected life Cambrian fossil trilobites: these creatures with a robust carapace were arthropods of the marine environment. | Nature Geoscience

The initial hypothesis. For a long time it was suspected that the percentage of atmospheric oxygen had been a determining factor in creating the conditions for these events, but the study is the first to find an important correlation between gas fluctuations and the massive appearance or disappearance of new species. Peak oxygen periods corresponded to sudden biodiversity developments and leaps forward in evolution; those of low oxygenation, due to extinction events - in a time frame in which the Cambrian explosion represents a fraction.

Mute testimonials. The evidence was found by analyzing the deep carbonate rocks of the Aldan and Lena rivers in Siberia, a region once covered by seas teeming with life. The levels of carbon and sulfur isotopes in these rocks are related to the amount of oxygen dissolved in the oceans and therefore present in the atmosphere. By studying the "isotopic signatures" the researchers reconstructed the trend of atmospheric oxygen fluctuations, which they then compared with the diversity of fossil animals corresponding to the same periods.

Through thick and thin. The findings revealed periods of strong diversification, but also "bottlenecks" in the spread of life and species, expansions and depressions corresponding to higher or lower percentages of oxygen in the atmosphere: the conclusion is that this factor therefore played a key role in determining the emergence of life on Earth.

In particular, confirm the analyzes, in a period that lasted over 13 million years in the Cambrian, there was a notable expansion of life: the Earth passed from being populated by immobile, unicellular organisms, to hosting sophisticated, bizarre forms of life and complex that later evolved into what we see today.

The study is the first to provide concrete evidence of the connection between oxygen and the mysterious explosion of biodiversity, still much debated, in the causes and modalities, by modern paleontologists.