May 29, 2023
Tree Rings Chronicle a mysterious cosmic storm that strikes every thousand years

Tree Rings Chronicle a mysterious cosmic storm that strikes every thousand years

The history of the bombardment of Earth with cosmic radiation is written in the trees.

Specifically, when radiation hits Earth’s atmosphere, it can change the nitrogen atoms it hits to produce a form of carbon, which is in turn absorbed by plants. Linking spikes in this carbon isotope to growth rings on trees can give us a reliable record of radiation storms going back thousands of years.

This record shows us that the most colossal of these events, known as Miyake events (after the scientist who discovered them), occur about once every thousand years. But we don’t know what causes them – and new research suggests that our leading theory, involving giant solar flares, could be out of the question.

Without an easy way to predict these potentially catastrophic events, we have a serious problem.

“We need to know more, because if one of these happened today, it would destroy technology, including satellites, internet cables, long-distance power lines and transformers,” says astrophysicist Benjamin Pope of the University of Queensland in Australia .

“The impact on global infrastructure would be unimaginable.”

The history of Earth’s encounters with cosmic ray storms is there to be deciphered if you know how to look. The main clue is a radioactive isotope of carbon called carbon-14, often referred to as radiocarbon. Compared to other naturally occurring carbon isotopes on Earth, radioactive carbon is relatively rare. It forms only in the upper atmosphere when cosmic rays collide with nitrogen atoms, triggering a nuclear reaction that creates radioactive carbon.

Because cosmic rays are constantly colliding with our atmosphere, we have a constant but very small amount of material raining down to the surface. Some of them get caught in tree rings. Since trees add a new growth ring each year, the radiocarbon deposit can be traced back in time, giving a record of radiation activity spanning tens of millennia.

A large spike in radiocarbon found in trees around the world means an increase in cosmic radiation. There are several mechanisms that can cause this, and solar flares are big. But there are some other possible sources of radiation storms that have not been definitively ruled out. Solar flares have not been definitively defined either.

Because interpreting tree-ring data requires a comprehensive understanding of the global carbon cycle, a team of researchers led by University of Queensland mathematician Qingyuan Zhang set out to reconstruct the global carbon cycle, based on every scrap of tree-ring radiocarbon data they could get. in the hands.

“When the radiation hits the atmosphere, it produces radioactive carbon-14, which filters into the air, oceans, plants and animals, and produces an annual record of radiation in tree rings,” Zhang explains.

“We modeled the global carbon cycle to reconstruct the process over a 10,000-year period to gain insight into the scale and nature of the Miyake events.”

The results of this modeling gave the team a highly detailed picture of some radiation events – enough to conclude that the timing and profile were inconsistent with solar flares. The spikes in radiocarbon are not correlated with sunspot activity, which is associated with flare activity. Some peaks persisted for many years.

And there was inconsistency in radiocarbon profiles between regions for the same event. For one major event, recorded in 774 CE, some trees in some parts of the world showed sharp, sudden increases in radiocarbon over a year, while others showed a slower spike over two to three years.

“Instead of a momentary burst or explosion, what we may be looking at is a kind of astrophysical ‘storm’ or explosion,” Zhang says.

Researchers don’t know, at this point, what might be causing these outbreaks, but there are several candidates. One of these is supernova events, the radiation from which can be launched into space. A supernova may have occurred in 774 CE, and scientists have made links between radiocarbon spikes and other possible supernova events, but we have known supernovae without radiocarbon spikes and spikes without associated supernovae.

Other possible causes include solar superflares, but a flare strong enough to produce the radiocarbon spike 774 CE is unlikely to have erupted from our Sun. Perhaps there is some previously unrecorded solar activity. But the fact is that there is no simple explanation that accurately explains what causes Miyake’s events.

And this, according to the researchers, is worrying. The human world has changed dramatically since 774 AD. a Miyake event now could trigger what scientists call a “cyberapocalypse,” as infrastructure breaks down, harms the health of air travelers, and even depletes the ozone layer.

“Based on the available data, there’s about a one percent chance we’ll see another within the next decade,” says Pope.

“But we don’t know how to predict it or what damage it might cause. These possibilities are quite alarming and set the stage for further research.”

The research has been published in Proceedings of the Royal Society A: Mathematical, Physical, and Engineering Sciences.

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