Scientists discover sixth mass extinction in Earth’s ancient past

(ORDO NEWS) — Extinctions periodically occur on our planet, that is, a large number of animal and plant species die out within a short geological time scale. They arose for various reasons.

For example, the last extinction occurred due to the fall of the Chicxulub meteorite 65 million years ago and led to the extinction of 70-75% of all terrestrial species, among which were all non-avian dinosaurs.

For a long time it was believed that there were only five mass extinctions in the history of our planet, and now, apparently, the sixth extinction has begun.

However, a recent study showed that in fact there were at least one more. The sixth extinction, previously unknown to science, occurred 550 million years ago, that is, at the very peak of life in the ocean. But why did it arise and what consequences did it lead to?

Was there a sixth extinction

The oldest extinction known to science occurred 440 million years ago. It is called Ordovician-Silurian. Then followed the Devonian extinction 365 million years ago. As a result of these two extinctions, many marine organisms disappeared.

After it was the “Great Dying”, or Permian-Triassic, which occurred 250 million years ago. This was followed by the Triassic-Jurassic extinction 201 million years ago, which we talked about earlier.

The most recent extinction occurred, as we said above, 65 million years ago, and affected the dinosaurs. Should one more be added to this list of extinctions?

This question remained open for a long time. The fact is that scientists have long recorded a sharp decline in biodiversity 550 million years ago. However, there was no evidence of a mass extinction.

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There have been five mass extinctions in Earth‘s history

The decline in biodiversity can be explained by various processes, for example, the ancient fauna could die because it began to compete in the same habitat with marine armored arthropods.

Or maybe the Ediacaran fauna did not die out at all, just at that moment there were no conditions for the emergence of fossils. As we said earlier, petrification is a complex process that occurs quite rarely and requires certain conditions.

Why did the mass extinction happen?

To summarize all of the above, scientists know that something happened to the fauna 550 million years ago, but what exactly is unknown.

To find out, the scientists compiled a database of Ediacaran fossils described earlier in the scientific literature. Moreover, they classified all the fossils according to several criteria – the geography of habitat, dietary habits, and body size.

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Extinct Ediacaran animals are very different from modern ones

The team ended up cataloging 70 animal species that existed before the supposed extinction. Of these, 56 species became extinct after 10 million years. However, scientists did not notice a change in the conditions that influenced the formation of fossils.

In addition, they did not find differences in the way of eating between the disappeared creatures and those who continued to live 10 million years later. This means that the Ediacaran animals did not die out due to competition with creatures that appeared later.

Then scientists took a closer look at the surviving creatures, and found they had one thing in common, which they reported in the journal Proceedings of the National Academy of Sciences.

The body structure of all the surviving species indicated that they could live in oxygen-deficient conditions. Combined with geochemical evidence of oxygen depletion, this suggests that the Ediacaran period ended in a mass extinction caused by a decrease in oxygen levels in the water.

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The sixth (first) extinction was caused by a decrease in oxygen levels in the ocean

The sixth extinction – why it is important to know about it

What caused the decrease in oxygen levels? Scientists cannot answer this question. There can be many reasons – volcanic eruptions, movements of tectonic plates, asteroids falling to Earth, etc. The only thing we can say with certainty is that the mass extinction influenced subsequent evolution, like all other extinctions.

According to the researchers, this work helps to understand the ecological and geological consequences of the lack of oxygen in the water.

The fact is that human activity leads to an increase in algae, which lowers the level of oxygen. Already now there are some areas where oxygen is not enough to sustain life. Over time, this can create serious problems for modern animals.


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