New study shows mysterious bursts of solar particles could destroy the ozone layer, showering Earth with radiation for years

The spectacular aurora at the beginning of May this year showed the power that solar storms can unleash as radiation, but every now and then the sun does something far more destructive. Known as “solar particle events,” these bursts of protons directly from the sun’s surface can shoot out like a searchlight into space.

Data shows that every thousand years the Earth is hit by an extreme solar particle event, which can cause severe damage to the ozone layer and increase the 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 Proceedings of the National Academy of Sciences. We also show that at times when the Earth’s magnetic field is weak, these events can have a dramatic effect on life across the planet.

Earth’s critical magnetic shield

Earth’s magnetic field provides a protective cocoon essential for life, deflecting electrically charged radiation from the sun. In its normal state, it works like a giant bar magnet with field lines rising from one pole, spinning around and dipping back to the other pole, in a pattern sometimes described as an “inverted grapefruit.” The vertical orientation at the poles allows some ionizing cosmic radiation to penetrate up into the upper atmosphere, where it interacts with gas molecules to create the glow we know as the aurora.

However, the field changes a lot over time. In the past century, the north magnetic pole has moved across northern Canada at a speed of about 40 kilometers per year and the field has weakened by more than 6%. The geological record shows that there have been periods of centuries or millennia when the geomagnetic field has been very weak or even 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 ancient past, and as a result much of its atmosphere. In May, not long after the aurora, a strong solar particle event hit 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 constantly fluctuating stream of electrons and protons known as the “solar wind”. However, the sun’s surface also sporadically emits bursts of energy, mostly protons, in solar particle events—which are often associated with solar flares.

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

Hundreds of weak solar particle events occur every solar cycle (roughly 11 years), but scientists have found traces of much stronger events throughout Earth’s history. Some of the most extreme were thousands of times louder than anything recorded with modern instruments.

Extreme solar particle events

These extreme solar particle events occur roughly every few millennia. The most recent occurred around 993 AD and was used to show that Viking buildings in Canada used felled timber in 1021 AD.

Less ozone, more radiation

Beyond their immediate effect, solar particle events can also set off a chain of chemical reactions in the upper atmosphere that can deplete ozone. Ozone absorbs harmful solar UV radiation, which can damage vision and also DNA (increasing the risk of skin cancer), as well as affecting 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 a year or more, increasing surface UV levels and increasing DNA damage. But if a solar proton event were to arrive during a period when the Earth’s magnetic field was very weak, then ozone depletion would last for six years, increasing UV levels by 25% and increasing the rate of damage to the Sun-induced DNA up to 50%.

Particle blasts from the past

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

In fact, this combination of events may explain some mysterious phenomena in Earth’s past.

The most recent period of weak magnetic field – including a temporary switch to the north and south poles – began 42,000 years ago and lasted about 1,000 years. Several major evolutionary events occurred around this time, such as the extinction of the last Neanderthals in Europe and the extinction of marsupial megafauna, including giant wombats and kangaroos in Australia.

An even larger evolutionary event has also been linked to the Earth’s geomagnetic field. The origin of multicellular animals at the end of the Ediacaran period (from 565 million years ago), recorded in 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 in 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 multiple unrelated groups has been described as the best means of detecting and avoiding harmful incoming UV rays, in a “flight from light”.

We are still 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.