Tree rings chronicle a mysterious cosmic storm that strikes every thousand years

The history of the bombing of the Earth with cosmic radiation is written on the trees.

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

This record shows us that the largest of these events, known as the Miyake events (after the scientist who discovered them), occur approximately once every thousand years. However, we don’t know what causes them — and new research suggests that our groundbreaking theory, which includes giant solar flares, could be off the table.

Without an easy way to predict these potentially devastating events, we’re left with a serious problem.

“We need to know more, because if one of these things happened today, it would destroy technology including satellites, internet cables, long-range 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 radiation storms is here to decipher 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 is formed only in the upper atmosphere, when cosmic rays collide with nitrogen atoms, resulting in a nuclear reaction that produces radioactive carbon.

Since cosmic rays are constantly colliding with our atmosphere, we have a steady but very small supply of material raining down on the surface. Some are hung in tree rings. As trees add a new growth ring each year, radiocarbon deposition can be traced through time, giving a record of radioactivity over tens of thousands of years.

A huge rise in radiocarbon found in trees around the world means a slight increase in cosmic radiation. There are many mechanisms that can cause this, and solar flares are significant. But there are some other potential sources of radiation storms that have not been conclusively ruled out. Solar flares have also not been definitively controlled.

Because interpreting tree-ring data entails a comprehensive understanding of the global carbon cycle, a team of researchers led by mathematician Chengyuan Zhang of the University of Queensland set out to reconstruct the global carbon cycle, based on every piece of tree-ring radiocarbon data they could obtain. Holding hands.

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

“We designed the global carbon cycle to reconstruct the process over 10,000 years, to gain insight into the scale and nature of Miyake events.”

The results of this modeling gave the team a very detailed picture of a number of radiative events – enough to conclude that the timing and profile do not correspond to solar flares. Mutations in radiocarbon are not related to sunspot activity, which is itself related to flare activity. Some of the upsides persisted over several years.

There was a discrepancy in the radiocarbon profiles between regions for the same event. For one major event, recorded in AD 774, some trees in some parts of the world showed sharp and sudden rises in radiocarbon for one year, while others showed slower rises over two to three years.

“Instead of a single instantaneous explosion or glow, what we might be looking at is some kind of astrophysical ‘storm’ or explosion,” Chang says.

Researchers don’t know, at this point, what could have caused those eruptions, but there are a number of candidates. One of these events is a supernova, the radiation from which can be blasted through space. The supernova likely occurred in 774 AD, and scientists have established 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 supersolar planets, but it is unlikely that an explosion strong enough to produce the 774 CE radiocarbon spike from our sun. There may have been some previously unrecorded solar activity. But the truth is that there is no simple explanation that accurately explains the causes of Miyake’s events.

This, according to the researchers, is a concern. The human world has changed dramatically since 774 AD. Now Miyake’s event may cause what scientists call an “internet apocalypse” where infrastructure is damaged, health of air travelers and even the ozone layer is depleted.

“Based on the available data, there’s about a 1% chance of seeing another one within the next decade,” Bob says.

“But we don’t know how to predict it or what harm it might cause. These possibilities are very worrying, and they lay the foundation for further research.”

The search was published in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

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