An extinction event 360 million years ago which caused the forest ecosystem to collapse was caused by a brief breakdown of the ozone layer, scientists have discovered.

And the researchers from the University of Southampton warn that the world could face a similar emergency as temperatures are predicted to rise to the same levels as the catastrophic event which “reset the evolution of our ancestors”.

The study, published in the journal Science Advances, shows that the ozone collapse occurred as the climate rapidly warmed following an intense ice age at the end of the Devonian geological period.

It states that the reduced ozone layer exposed the Earth to high levels of UV radiation, causing forest ecosystems to collapse and killing off many species of fish and tetrapods – the four-limbed ancestors of humans.

Professor John Marshall, of Southampton’s School of Ocean and Earth Science, said: “Our ozone shield vanished for a short time in this ancient period, coinciding with a brief and quick warming of the Earth.

“Our ozone layer is naturally in a state of flux – constantly being created and lost – and we have shown this happened in the past too, without a catalyst such as a continental scale volcanic eruption.”

He continued: “Current estimates suggest we will reach similar global temperatures to those of 360 million years ago, with the possibility that a similar collapse of the ozone layer could occur again, exposing surface and shallow sea life to deadly radiation.

“This would move us from the current state of climate change, to a climate emergency.”

The team collected rock samples during expeditions to mountainous polar regions in East Greenland, which once formed a huge ancient lake bed in the arid interior of the Old Red Sandstone Continent, made up of Europe and North America.

The rocks were dissolved in hydrofluoric acid, releasing microscopic plant spores similar to pollen but from fern-like plants which had lain preserved for hundreds of millions of years.

On microscopic examination, the scientists found many of the spores had bizarrely formed spines on their surface which the scientists say was a response to the increased UV radiation damaging their DNA.

Also, many spores had dark pigmented walls, thought to be a kind of protective “tan”, due to increased and damaging UV levels.

The scientists believe that during the extinction some plants survived but ecosystems collapsed, and in the seas, the dominant group of armoured fish became extinct, and the sharks and bony fish that survived remain the dominant fish.

The researchers also say that the extinction reset the direction of the evolution of tetrapods, leading them to become terrestrial dwellers with the number of fingers and toes reduced to five.