Erosion of Ozone Layer Spurred Mass Extinction Event

Normal and malformed spores from East Greenland. (Photo by John Marshall)

(CN) — One of the most significant extinction events in Earth’s history occurred because of a short but critical failure of Earth’s ozone layer millions of years ago — a failure that could point to a potentially dire future.

During a lifespan that stretches across billions of years, Earth is no stranger to extinction events. These devastating and cataclysmic occurrences have come in many forms throughout the years, be it a massive asteroid that wiped out the dinosaurs or a series of powerful volcanic eruptions that threw Earth’s atmosphere into chemical chaos. Regardless of the form they took or the damage they dealt, each event played an important role in fundamentally shaping Earth’s existence.

Researchers now believe that they have identified the cause of another extinction event, one that may prove eerily relevant to today’s climate change crisis.

In a study published Wednesday in Science Advances, researchers from the University of Southampton revealed that an extinction event roughly 360 million years ago was directly caused by a temporary erosion of Earth’s ozone layer.

The ozone layer acts as a shield that protects Earth’s surface from harmful ultraviolet radiation emitted by the sun. But researchers suggest that this protective shield suffered a brief but massive failure millions of years ago, allowing UV radiation to do untold damage to Earth’s surface.

This lapse, scientists say, singlehandedly destroyed entire forest ecosystems and killed much of Earth’s freshwater aquatic life. This included the dominant group of armored fish at the time and different types of tetrapods, types of fish that evolved with limbs instead of fins and were some of the earliest ancestors to humans.

Researchers say the event took place during the end of the Devonian period, shortly after Earth came out of an extended ice age. Earth’s temperatures suddenly and drastically rose and the heat generated the chemicals needed to erode the ozone layer.

This left Earth all but defenseless to harsh UV radiation for the next several thousand years.

“Our ozone shield vanished for a short time in this ancient period, coinciding with a brief and quick warming of the Earth,” John Marshall, of the University of Southampton’s School of Ocean and Earth Science and a National Geographic Explorer, said with the release of the study. “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.”

Researchers made this discovery by studying rock samples taken from locations around the world that were geographically significant during the Devonian period, such as East Greenland and the Andean Mountains in Bolivia. After submerging the rocks in hydrofluoric acid, the rocks released a number of special plant spores that had been preserved in them for millions of years.

These spores ultimately revealed to scientists the bigger picture. Upon closer microscopic analysis, researchers found that many of the spores were scarred with oddly shaped surface spines and darker tans on their cellular walls.

Scientists concluded that these marks were the result of DNA damage caused by intense UV radiation during the UV radiation extinction event.

Researchers warn that this illuminating discovery holds potentially dark significance. With current models projecting the possibility of Earth reaching the kinds of temperatures seen 360 million years ago, researchers say that an ozone collapse like the one seen during the Devonian period could happen again.

Should this take place, researchers say, the amount of harmful radiation Earth would be exposed to could prove globally severe.

Marshall said that as dire as these discoveries may sound, learning and understanding them is preferable to ignorance.

“With pandemics and global warming, you would wonder why we need to know about another way we are all going to die,” Marshall said in an email. “However, the parallel is with the discovery that an asteroid impact caused the extinction of the dinosaurs amongst other ancient life forms. So, we can now identify the threat, study it, model the process and evaluate the likely risk. Is it real, what is the time scale etc. We can then make informed decisions. We should see it as a warning from deep time.”

Marshall said, however, there is still much work and scientific discourse to be done before the problem is fully understood.

“I think it’s a major discovery that changes the way we should regard the ozone as a barrier that’s not permanent and thickens and thins,” Marshall said. “However, there is an enormous amount of work to do and the scientific community will or should have a quite intense debate. For example, it’s taken 40 years to finally resolve the issue of dinosaur extinctions.”

He added: “The bottom line is that we should be rather concerned.”

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