This article was originally published on Conversation. The publication contributed to the article on Space.com Expert Voices: Op-Ed & 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 spectacular aurora at the beginning of May this year showed the power that solar storms can emit as radiation, but from time to time SUN it does something much more destructive. Known as “solar particle events,” these explosions of protons directly from the surface of the sun can shoot like a searchlight at ROOM.
The data show that every thousand years 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 one newspaper published today. We also show this at times when the Earth 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.
Connected: We may have witnessed some of the strongest auroras in 500 years
However, the field varies greatly 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 from 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 the Earth’s magnetic field by looking March, which lost its global magnetic field in the ancient past, and as a result most of its atmosphere. In May, not long after the aurora, a strong solar particle event hit Mars. It stopped working Mars Odyssey spacecraft and caused radiation levels on the surface of Mars about 30 times higher than you would get during a chest X-ray.
The power of protons
The sun’s outer atmosphere emits a continuous oscillating current electrons and protons known as “the solar windHowever, the sun’s surface also sporadically emits bursts of energy, mostly protons, in solar particle events – which are often accompanied by 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 year solar cycle (approximately 11 years), but scientists have found traces of much stronger events during 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 latest occurred around 993 AD and was used to indicate that Viking buildings in Canada used wood cut 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 ours 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 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. Some major evolutionary events happened around this timesuch as the extinction of the last Neanderthals in Europe and extinctions of marsupial megafauna including Wombats and giant kangaroos in Australia.
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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 Australiahappened after a period of 26 million years 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 “light flight”.
We are still beginning to explore the role of solar activity and the Earth’s magnetic field in the history of life.