Extreme blasts from Sun once in thousand years can be catastrophic to life on Earth

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About every thousand years an extreme blast from the Sun’s surface “like a searchlight into space” can severely disrupt the Earth’s ozone layer and impact all life on Earth, a new study warns.

This extreme “solar particle event” can expose people to high levels of harmful UV radiation, causing high cancer rates, and even lead to changes in global climate, researchers, including those from ETH, Zürich say.

The study, published in the journal PNAS, assessed what could happen on Earth during such an extreme event, especially at times when the planet’s protective magnetic shield is weaker.

Normally, the Earth’s magnetic field protects the planet by deflecting charged particles in space, but this magnetic shield’s strength can vary.

Meanwhile, the Sun’s surface also emits highly energetic protons in what are called “solar particle events” that can reach as far as the lower altitudes in Earth’s atmosphere.

But about every millennium, there may be extreme solar particle events “thousands of times stronger than anything recorded with modern instruments”, researchers write in The Conversation.

“These blasts of protons directly from the surface of the Sun can shoot out like a searchlight into space,” they say.

While contemporary solar particle events are weak and easily deflected by Earth’s magnetic field, extreme ones have occurred in the past, researchers warn.

Such an extreme event can tumble a cascade of dominoes in the Earth’s ozone layer and disrupt it for over a year, scientists warn.

Without the ozone layer, harmful UV radiation can reach the planet’s surface, damaging DNA in all lifeforms.

“Very high intensities of UV-B radiation could hinder plant growth and photosynthesis and generate elevated levels of DNA damage across many species,” researchers wrote.

In humans, it may lead to a heightened risk of skin cancer, cataracts, and impaired immune function with eye damage symptoms starting as early as 30 min to 12 hours after UV radiation exposure.

If such a blast from the Sun were to reach the Earth during a period when the planet’s magnetic field is much weaker, then the damage to the ozone layer may last for nearly six years.

This may increase UV levels reaching Earth by 25 per cent and DNA damage by up to 50 per cent, which can be catastrophic to crops grown across the globe.

“The resulting ground-level ultraviolet radiation would remain elevated for up to 6 y, leading to increases in UV index up to 20 to 25 per cent and solar-induced DNA damage rates by 40 to 50 per cent,” researchers wrote.

The widespread DNA damage may also spur periods of evolution such as the rapid diversification of animals during the Cambrian Explosion period about 539 million years ago.

“During those periods, cosmic ionizing particles can enter Earth’s atmosphere at lower latitudes and damage the ozone layer, resulting in marked increases in surface UV radiation,” scientists wrote.

“Potential consequences include serious health hazards and longer-term climatic and evolutionary impacts,” they said.

One such extreme solar blast likely affected hunter–forager groups about 42,200 and 41,500 years ago and may have caused the disappearance of the last Neanderthals, scientists suspect now.