New study shows mysterious solar particle explosions can devastate the ozone layer, bathing Earth in radiation for years

The remarkable northern lights in early May demonstrated the power of radiation from solar storms, but sometimes the sun does something far more destructive. Known as “solar particle events,” these proton explosions directly from the sun’s surface can be projected into space like a searchlight.

Data shows that Earth is hit by an extreme solar particle event about every thousand years, which could cause severe damage to the ozone layer and increase levels of ultraviolet (UV) radiation at the surface.

We analyzed what happens during such an extreme event in an article published on July 1 in the Proceedings of the National Academy of SciencesWe also show that at times when Earth’s magnetic field is weak, these events could have a dramatic effect on life across the planet.

Earth’s Essential Magnetic Shield

The Earth’s magnetic field provides a protective cocoon essential to life, deflecting electrically charged radiation from the Sun. In its normal state, it functions like a giant bar magnet, with field lines rising from one pole, looping around, and descending to the other pole, in a pattern sometimes described as an “upside-down grapefruit.” The vertical orientation of the poles allows some ionizing cosmic radiation to penetrate into the upper atmosphere, where it interacts with gas molecules to create the glow we know as the aurora.

However, the magnetic field changes considerably over time. Over the past century, the North Magnetic Pole has moved across northern Canada at a rate of about 40 kilometres per year, and the magnetic field has weakened by more than 6%. Geological records show that there have been periods of centuries or millennia when the geomagnetic field has been very weak or completely absent.

We can see what would happen without Earth’s magnetic field by looking at Mars, which lost its global magnetic field in the distant past, and much of its atmosphere as a result. In May, shortly after the aurora borealis, a powerful solar particle event struck Mars. It disrupted the Mars Odyssey spacecraft and caused radiation levels on the Martian surface about 30 times higher than what you would get during a chest X-ray.

The power of protons

The Sun’s outer atmosphere emits a constant and fluctuating stream of electrons and protons known as the “solar wind.” However, the Sun’s surface also sporadically emits bursts of energy, primarily protons, during solar particle events, often associated with solar flares.

Protons are much heavier than electrons and carry more energy. They therefore reach lower altitudes in the Earth’s atmosphere, exciting gas molecules in the air. However, these excited molecules only emit X-rays, invisible to the naked eye.

Hundreds of faint solar particle events occur every solar cycle (about 11 years), but scientists have found evidence of much more powerful events throughout Earth’s history. Some of the most extreme events were thousands of times more powerful than anything recorded with modern instruments.

Extreme solar particle events

These extreme solar particle events occur approximately every few millennia. The most recent occurred around 993 AD and has been used to show that Viking buildings in Canada used wood cut in 1021 AD.

Less ozone, more radiation

Beyond their immediate effects, solar particles can also trigger a chain of chemical reactions in the upper atmosphere that can deplete the ozone layer. Ozone absorbs the sun’s harmful UV rays, which can damage eyesight and DNA (increasing the risk of skin cancer), as well as impacting the climate.

In our new study, we used large computer models of global atmospheric chemistry to examine the impacts of an extreme solar particle event.

We found that such an event could deplete ozone levels for about a year, increasing UV levels at the surface and increasing DNA damage. But if a solar proton event occurred during a period when the Earth’s magnetic field was very weak, the ozone damage would last for six years, increasing UV levels by 25% and increasing the rate of solar-induced DNA damage by up to 50%.

Particle explosions from the past

How likely is this deadly combination of a weak magnetic field and extreme solar proton events? Given how often each of these phenomena occurs, it seems likely that they occur together relatively often.

In fact, this combination of events could explain several mysterious events that occurred in Earth’s past.

The most recent period of weak magnetic field, which included a temporary reversal of the North and South poles, began 42,000 years ago and lasted about 1,000 years. Several major evolutionary events occurred during this time, such as the disappearance of the last Neanderthals in Europe and the extinction of marsupial megafauna, including giant wombats and kangaroos in Australia.

An even more important evolutionary event has also been linked to the Earth’s magnetic field. The appearance of multicellular animals at the end of the Ediacaran period (565 million years ago), attested by fossils in the Flinders Ranges of South Australia, occurred after a 26-million-year period of weak or absent magnetic field.

Similarly, the rapid evolution of various animal groups during the Cambrian explosion (about 539 million years ago) has also been linked to geomagnetism and high UV levels. The simultaneous evolution of eyes and hard body shells in several unrelated groups has been described as the best way to detect and avoid incoming harmful UV rays, in a “light escape.”

We are only beginning to explore the role of solar activity and the Earth’s magnetic field in the history of life.

This article is republished from The Conversation under a Creative Commons license. Read the original article.