This article was originally published in The conversation. The publication contributed to the article for Space.com. Expert Voices: Opinion articles and opinions.
Alan Cooper He is a professor at Charles Sturt University
Pavle Arsenovic is a senior scientist at the University of Natural Resources and Life Sciences (BOKU).
The remarkable aurora in early May this year demonstrated the power that solar storms can emit as radiation, but occasionally Sun does something much more destructive. Known as “solar particle events,” these explosions of protons directly from the surface of the sun can be fired like a reflector towards space.
Records show that approximately every thousand years Land is hit by an extreme solar particle event, which could cause severe damage to the ozone layer and increase ultraviolet (UV) radiation levels at the surface.
We analyze what happens during such an extreme event in a Article published todayWe 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 critical magnetic shield
Earth's magnetic field provides a crucial protective cocoon for life, deflecting electrically charged radiation from the sun. In its normal state, it functions like a giant magnet with field lines rising from one pole, circling around, and then descending again at the other pole, in a pattern sometimes described as an “inverted grapefruit.” The vertical orientation at the poles allows some of the ionizing cosmic radiation to penetrate all the way to 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 auroras in 500 years.
However, the field changes a lot over time. timeOver the past century, the magnetic north pole has been drifting across northern Canada at a rate of about 40 kilometers per year, and the field has weakened. more than 6%Geological records show 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 observing Marswhich lost its global magnetic field in the ancient past and, as a result, most of its atmosphere. In May, shortly after the aurora, A strong solar particle event hit Mars. Interrupted the operation of the Odyssey on Mars spacecraft and caused radiation levels on the surface of Mars to be about 30 times higher than what you would receive during a chest X-ray.
The power of protons
The Sun's outer atmosphere emits a constant fluctuating stream of electrons and protons known as “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 have more energy, so they reach lower altitudes in Earth's atmosphere, exciting gas molecules in the air. However, these excited molecules only emit X-rays, which are invisible to the naked eye.
Hundreds of faint solar particle events occur each year. solar cycle (about 11 years), but scientists have found traces of much stronger events throughout Earth's history. Some of the most extreme were thousands of times stronger 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 was used to show that Viking buildings in Canada used Wood cut in 1021 AD.
Less ozone, more radiation
Beyond their immediate effect, solar particle phenomena can also trigger a chain of chemical reactions in the upper atmosphere that can deplete ozone. Ozone absorbs harmful solar ultraviolet radiation, which can damage eyesight and DNA (increasing the risk of skin cancer), as well as affecting the climate.
In our New studyWe use large computer models of global atmospheric chemistry to examine the impacts of an extreme solar particle event.
We found that such an event could reduce ozone levels for about a year, which would raise UV levels at the surface and increase DNA damage. But if a solar proton event occurred during a period when 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 bursts from the past
How likely is it that this deadly combination of weak magnetic field and extreme solar proton events will occur? Given how frequently each occurs, it seems likely that they occur together relatively frequently.
In fact, this combination of events may explain several mysterious events in Earth's past.
The most recent period of weak magnetic field, which includes a temporary shift between the north and south poles, began 42,000 years ago and lasted about 1,000 years. Several important evolutionary events It happened at this timesuch as the disappearance of the last Neanderthals in Europe and the Extinctions of marsupial megafauna including Giant wombats and kangaroos in Australia.
An even greater evolutionary event has also been linked to the Earth's geomagnetic field. The origin of multicellular animals in the late Ediacaran period (565 million years ago), recorded in Fossils in the Flinders Ranges of South Australiaoccurred after a period of 26 million years weak or absent magnetic field.
Similarly, the rapid evolution of diverse animal groups in the Cambrian Explosion (about 539 million years ago) has also been linked to geomagnetism and high levels of ultraviolet light. The simultaneous evolution of eyes and hard body shells in multiple unrelated groups has been linked to the evolution of eyes and hard body shells in multiple unrelated groups. described as the best means of detecting and avoiding harmful incoming UV rays, in a “flight from light” fashion.
We are still beginning to explore the role of solar activity and the Earth's magnetic field in the history of life.
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