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New study shows mysterious solar particle blasts can devastate the
ozone layer, bathing Earth in radiation for years
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Credit: Harrison Haines from Pexels
The remarkable aurora in early May this year demonstrated the power
that solar storms can emit as radiation, but occasionally the sun does
something far more destructive. Known as "solar particle events,"
these blasts of protons directly from the surface of the sun can shoot
out like a searchlight into space.
Records show that around every thousand years Earth gets 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 paper
published July 1 in the _Proceedings of the National Academy of
Sciences_. We also show that at times when Earth's 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 the normal
state, it functions like a gigantic bar magnet with field lines rising
from one pole, looping around, and plunging back down at 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 down as far as the upper atmosphere, where it
interacts with gas molecules to create the glow we know as the aurora.
However, the field changes a great deal over time. In the past
century, the north magnetic pole has wandered across northern Canada
at a speed of around 40 kilometers per year, and the field has
weakened by more than 6%. Geological records show there have been
periods of centuries or millennia when the geomagnetic field has been
very weak or even entirely 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
most of its atmosphere as a result. In May, not long after the aurora,
a strong solar particle event hit Mars. It disrupted the operation of
the Mars Odyssey spacecraft, and caused radiation levels at the
surface of Mars 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 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 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 stronger than anything recorded with modern
instruments.
## Extreme solar particle events
These extreme solar particle events occur roughly every few millennia.
The most recent one happened around 993 AD, and was used to show that
Viking buildings in Canada used timber cut in 1021 AD.
## Less ozone, more radiation
Beyond their immediate effect, solar particle events can also
kickstart a chain of chemical reactions in the upper atmosphere that
can deplete ozone. Ozone absorbs harmful solar UV radiation, which can
damage eyesight and also DNA (increasing the risk of skin cancer), as
well as impacting 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 such an event could deplete ozone levels for a year or so,
raising UV levels at the surface and increasing DNA damage. But if a
solar proton event arrived during a period when Earth's magnetic field
was very weak then ozone damage would last six years, increasing UV
levels by 25% and boosting the rate of solar-induced DNA damage by 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 them occurs, it
appears likely they happen together relatively often.
In fact, this combination of events may explain several mysterious
occurrences in Earth's past.
The most recent period of weak magnetic field—including a temporary
switch in 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 disappearance of the last Neanderthals in
Europe and the extinctions of marsupial megafauna including giant
wombats and kangaroos in Australia.
VIDEO
An even bigger evolutionary event has also been linked to 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 South Australia's Flinders Ranges, occurred after a 26-million-year
period of weak or absent magnetic field.
Similarly, the rapid evolution of diverse groups of animals in the
Cambrian Explosion (around 539 million years ago) has also been
related 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 to both detect and avoid the harmful
incoming UV rays, in a "flight from light."
We are still only starting to explore the role of solar activity and
Earth's magnetic field in the history of life.
**More information:** Pavle Arsenović et al, Global impacts of an
extreme solar particle event under different geomagnetic field
strengths, _Proceedings of the National Academy of Sciences_ (2024).
DOI: 10.1073/pnas.2321770121
This article is republished from The Conversation under a Creative
Commons license. Read the original article.
**Citation** : New study shows mysterious solar particle blasts can
devastate the ozone layer, bathing Earth in radiation for years (2024,
July 2) retrieved 3 July 2024 from
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devastate.html
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