(ORDO NEWS) — Throughout history, at least five major mass extinctions have occurred on Earth, during which a large part of life across the globe has died.
Most of these events quite clearly coincided with such disasters as asteroid impacts, geological activity and volcanic eruptions.
One event, however, is more of a mystery – the extinction of the Late Devonian 360 million years ago. Scientists have not found significant effects of asteroids since that time, and there are no records of mercury indicating strong volcanism.
What we know is that at that time the world became warmer as it emerged from the ice age. This alone would not necessarily be enough for mass extinction, but now scientists have found new evidence.
The fossil data suggests a sharp increase in ultraviolet radiation caused by the temporary depletion of the ozone layer as the world warms up.
This is an alarming conclusion – because it suggests that the depletion of the ozone layer could be a natural response to global warming. And the world is heating up with destructive speed right now.
Extinction in the Late Devonian occurred between 500,000 and 25 million years, killing up to 80 percent of all animal species living at that time. But it also had a devastating effect on plants.
“With regard to pollen and spores, the extinction of the Earth is clearly expressed as a complete loss of diversity at the Devonian-Carboniferous (DC) border with the extinction of at least the four main groups of spores that dominated the spore community,” the researchers write .
A previous study in 2018 showed that fossilized plant spores resulting from the Permian-Triassic extinction 252 million years ago were severely affected by ultraviolet radiation. This malformation prevented the reproduction of plants, which led to the mass extinction of vegetation.
This was due to depletion of the ozone layer due to strong volcanic activity. But such an explanation is not suitable for the late Devonian extinction (remember, no volcanic eruptions known to us), but it is possible that something else could deplete the ozone layer. Therefore, the research team turned to fossilized plant spores.
Researchers collected rock samples from sites in Greenland, which was closer to the equator during the Late Devonian, and studied them for fossilized plant spores. And they found that many of the spores showed signs of damage from ultraviolet radiation.
Prickly spores of a plant called Grandispora cornuta began to appear with irregular spikes and irregular shapes (pictured above). And many of the spores were darker in color — probably pigmentation designed to protect against more intense ultraviolet radiation.
Scientists concluded that the ozone layer was indeed thinned, increasing the amount of ultraviolet radiation that hits the Earth’s surface, destroying a large number of plant species. And since plants form the backbone of the food web, this has had a cascading effect, destroying herbivores and then carnivores.
So what caused the depletion of the ozone layer? Warming itself, scientists say. As temperature rises, natural fluorocarbons, such as methyl chloride, rise into the atmosphere, acting as a catalyst for the destruction of the ozone layer.
“Current estimates suggest that we can reach global temperatures similar to those that were 360 million years ago, with the possibility that a similar collapse of the ozone layer could occur again, exposing earthly life to deadly radiation,” said scientist John Marshall, University of Southampton In Great Britain.
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