Two of Earth's mass extinctions were caused by something much worse than asteroids

Human societies often focus on dangers that exist here on Earth, but there are moments when the threats might come from much farther away.

Scientists have long wondered about cosmic events that can affect our planet’s biology. Some have been exploring whether powerful stellar explosions could be tied to catastrophic shifts in Earth’s distant past.

The idea that blasts from massive stars might have influenced global conditions is catching attention.

Two large-scale losses of life have drawn renewed interest from researchers who see a pattern in the timing of star explosions and severe changes in Earth’s environment.

In a new study from Keele University, lead author Dr. Alexis Quintana, formerly of Keele and now at the University of Alicante, worked with Dr. Nick Wright from Keele to examine the distribution of massive stars in our region of the galaxy.

The study found that the rate of these stars going supernova near Earth appears to match two large ancient losses of life that happened 372 million years ago and 445 million years ago.

Past mass extinctions

Scientists refer to these moments in Earth’s past as the late Devonian and Ordovician events.

The first occurred about 372 million years ago and led to the disappearance of around 70 percent of all species, shifting the balance of aquatic life.

The second happened 445 million years ago, removing 60 percent of marine invertebrates at a time when life mostly existed in the sea.

Researchers have struggled to nail down a clear spark for those events, though many have pointed to an erosion of the ozone layer.

Some now propose that cosmic detonations may have stripped away that protective layer, allowing intense ultraviolet light to reach Earth’s surface.

Supernovas within Earth’s reach

The authors say it is “a great illustration for how massive stars can act as both creators and destructors of life”.

These stars generate heavy elements that make planets possible, but their demise can produce bursts of radiation.

The team embarked on what they call a “census” of nearby massive stars, known as OB stars, within around 3,260 light-years of the Sun.

OB stars are giants that can collapse under gravity when they run out of fuel, leading to an explosion that releases intense waves of energy.

The researchers then calculated how often these explosions might happen within 65 light-years of Earth, which is about 20 parsecs.

By comparing those estimates with the frequency of major losses of life linked to external triggers, they found a match that points to a nearby supernova as a likely suspect in the late Devonian and Ordovician events.

“We calculated the supernova rate close to Earth and found it to be consistent with the rate of mass extinction events on our planet that have been linked to external forces such as supernovae,” Dr Wright explained.

What would a supernova do to Earth

The study suggests that a supernova near Earth might erode the ozone layer, spark chemical reactions that produce acid rain, and expose organisms to harmful solar radiation.

“Supernova explosions bring heavy chemical elements into the interstellar medium, which are then used to form new stars and planets. Dr. Quintana explained.

“But if a planet, including the Earth, is located too close to this kind of event, this can have devastating effects.”

If enough shielding is lost, regions of the planet might become biologically hazardous. This could halt the growth of some organisms while allowing others to take over previously occupied niches.

Dr Wright added, “Supernova explosions are some of the most energetic explosions in the universe. If a massive star were to explode as a supernova close to the Earth, the results would be devastating for life on Earth. This research suggests that this may have already happened.”

He and his colleagues see the new data as helpful for understanding how elements move around the galaxy and form the basis for new celestial objects.

Why does any of this matter?

Supernova events are believed to happen at a rate of about one or two per century in galaxies such as the Milky Way. The chance of one erupting in our immediate neighborhood is low, though not impossible.

The researchers note that stars like Antares and Betelgeuse might run out of fuel in the next million years or so, yet they sit far enough away that the effects on Earth are likely limited.

The project’s census of massive stars also aids in studying black holes and neutron stars, which arise from the aftermath of stellar collapses.

The data can support improvements to gravitational wave detectors, which help scientists pinpoint the origins and structure of cosmic events.

By refining how often massive stars explode, astronomers can hone their forecasts for how often gravitational waves ripple through space.

Earth, supernovas, and future study

Plenty of questions remain about the ways in which these explosions can set off harmful changes in Earth’s environment.

Some experts wonder how quickly the atmosphere recovers if solar radiation spikes. Others are curious if life on land reacts differently from life at sea when cosmic rays increase.

Although researchers highlight a connection between supernovae and serious biological upheavals, there could be additional processes at work.

These blasts may seed the universe with valuable ingredients while also posing potential dangers when they happen too close for comfort.

The evidence is still coming together, but it points to a story where Earth’s ancient tragedies may have a cosmic explanation. Scientists plan to keep tracking massive stars in our galaxy to see what more can be learned.

The full study was published in the journal Monthly Notices of the Royal Astronomical Society.

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