This article was originally published on The conversation. The publication contributed to the Space.com article Expert Voices: Editorials and Reflections.
Alan Cooper is a professor at Charles Sturt University
Pavle Arsenovic is a senior scientist at Natural Resources and Life Sciences University (BOKU).
The remarkable aurora in early May this year demonstrated the power that solar storms can emit in the form of radiation, but sometimes the sun does something far more destructive. Known as “solar particle events,” these explosions of protons directly from the surface of the sun can shoot out like a spotlight into space.
Records show that approximately every thousand years Earth is hit by an extreme solar particle event, 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 a article published today. We also show that at times when the Earth 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 acts as 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 back down at 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.
Related: We may have just witnessed some of the strongest northern lights in 500 years
However, the field changes a lot over time. timeOver the past century, the north magnetic pole has moved across northern Canada at a rate of about 40 kilometres 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 was very weak or even completely absent.
We can see what would happen without the Earth’s magnetic field by looking Marchwhich lost its global magnetic field in the distant past, and most of its atmosphere as a result. In May, shortly after dawn, A powerful solar particle event hit Mars. This disrupted the functioning of the Mars Odyssey spacecraft and caused radiation levels on the surface of Mars about 30 times higher than what you would receive in 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 “solar windHowever, the Sun’s surface also sporadically emits bursts of energy, primarily protons, during solar particle events – which are 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 weak 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 millenniaThe 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 studyWe 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 – including a temporary reversal of the north and south poles – began 42,000 years ago and lasted about 1,000 years. Several major evolutionary events happened at that timesuch as the disappearance of the last Neanderthals in Europe and the extinctions of marsupial megafauna including Wombats and giant kangaroos in Australia.
To watch
An even more important evolutionary event has also been linked to the Earth’s geomagnetic field. The origin of multicellular animals at the end of the Ediacaran period (565 million years ago), recorded in Fossils in the Flinders Ranges in South Australiaoccurred after a period of 26 million years 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 describe as the best way to detect and avoid incoming harmful UV rays, in a “light leak”.
We are only beginning to explore the role of solar activity and the Earth’s magnetic field in the history of life.