This article was originally published on The conversation. The publication contributed the article to Space.com Expert Voices: Opinion Pieces and Insights.
Alan Cooper is a professor at Charles Sturt University
Pavle Arsenovic is a senior scientist at the University of Natural Resources and Life Science (BOKU).
The remarkable aurora borealis in early May this year showed the power that solar flares can emit as radiation, but occasionally the sun does something much more destructive. These explosions, known as “solar particle events”, protons directly from the surface of the sun can shoot into space like a searchlight room.
Data shows that approximately every thousand years Soil is hit by an extreme solar particle explosion, which could cause serious damage to the ozone layer and increase the amount of ultraviolet (UV) radiation at the Earth’s surface.
We have analyzed what happens during such an extreme event in a article published todayWe also show that at times when the Earth magnetic field weak, these events can have a dramatic effect on life across the planet.
The Earth’s Critical Magnetic Shield
The Earth’s magnetic field provides a crucial protective cocoon for life by 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 it, and diving back down at the other pole in a pattern sometimes described as an “inverted grapefruit.” The vertical orientation at the poles allows ionizing cosmic rays to penetrate into the upper atmosphere, where they interact with gas molecules to create the glow known as the aurora borealis.
Related: We may have just seen one of the strongest northern lights in 500 years
However, the field changes dramatically over time. timeOver the past century, the magnetic north pole has moved across northern Canada at a rate of about 40 kilometers per year, and the field has weakened by more than 6%Geological data show that there have been periods of centuries or millennia when the Earth’s magnetic field was very weak or even absent altogether.
We can see what would happen without the Earth’s magnetic field by looking at Marswhich in the distant past lost its global magnetic field, and most of its atmosphere as a result. In May, not long after the aurora, a strong explosion of solar particles hit Mars. It disrupted the functioning of the Mars Odyssey spacecraft and produced radiation levels on the Martian surface about 30 times higher than what you would expect from a chest X-ray.
The power of protons
The Sun’s outer atmosphere emits a constant, fluctuating stream of electrons and protons known as the “solar wind.” However, the Sun’s surface also sporadically emits bursts of energy, usually 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 faint solar particle events occur every day solar cycle (about 11 years) but scientists have found traces of much stronger events in Earth’s history. Some of the most extreme were thousands of times stronger than anything recorded by modern instruments.
Extreme solar particle events
These extreme solar particle events are happening about every few millenniaThe most recent occurred around 993 AD and was used to demonstrate that Viking buildings were present in Canada wood cut in 1021 AD..
Less ozone, more radiation
In addition to their direct effect, solar particles can also trigger a series of chemical reactions in the upper atmosphere that can deplete ozone. Ozone absorbs harmful UV radiation from the sun, which can damage vision and also DNA (increasing the risk of skin cancer), and can also affect the climate.
In our new studyWe used large computer models of global atmospheric chemistry to investigate the effects of an extreme solar particle explosion.
We found that such an event could reduce ozone levels for about a year, increasing UV levels at the Earth’s 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 weak magnetic field and extreme solar proton events? Given how common each is, it seems likely that they occur together relatively often.
This combination of events may provide an explanation for a number of mysterious events from Earth’s past.
The most recent period of weak magnetic field – including a temporary switching of the north and south poles – began 42,000 years ago and lasted about 1,000 years. Several key evolutionary events took place around this timesuch as the disappearance of the last Neanderthals in Europe and the extinction of marsupial megafauna included giant wombats and kangaroos in Australia.
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An even larger evolutionary event is also 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 diverse groups of animals 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 is described as the best way to detect and avoid the harmful incoming UV radiation, in a “flight from the light”.
We are only at the beginning of our investigation into the role of solar activity and Earth’s magnetic field in the history of life.