Tree Ring’s chronicle of a mysterious cosmic storm that strikes every thousand years

The history of the bombardment of the earth by cosmic rays is written in the trees.

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

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

Without an easy way to predict these potentially devastating events, we face a serious problem.

“We need to know more because if something like this happened today it would destroy technology like satellites, internet cables, transmission 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, radiocarbon is relatively rare. It only forms in the upper atmosphere when cosmic rays collide with nitrogen atoms and start a nuclear reaction that produces radiocarbon.

Because cosmic rays are constantly colliding with our atmosphere, we have a constant but very small supply of the stuff raining down on the surface. Part of it gets caught in tree rings. As trees add a new growth ring each year, radiocarbon deposition can be traced back through time, providing a record of radiation activity spanning tens of thousands of years.

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

Because interpreting tree-ring data requires a thorough 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 their hands on Open your hands.

“When radiation hits the atmosphere, it produces radioactive carbon-14, which filters through the air, oceans, plants and animals, creating 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 magnitude and nature of the Miyake events.”

The results of this modeling provided the team with an extremely detailed picture of a series of radiative events – enough to conclude that the timing and profile was not consistent with solar flares. The spikes in radiocarbon do not correlate with sunspot activity, which itself is linked to flare activity. Some peaks lasted for several years.

And there were discrepancies in radiocarbon profiles between regions for the same event. In a major event recorded in AD 774, some trees in some parts of the world showed a sharp, sudden increase in radiocarbon for a year, while others showed a slower increase over two to three years.

“Rather than a single instantaneous explosion or flare, we may be seeing some sort of astrophysical ‘storm’ or burst,” says Zhang.

Researchers don’t know at this point what could be causing these outbreaks, but there are a number of candidates. One of them is supernova events, whose radiation can penetrate space. A supernova may have occurred in AD 774, and scientists have made connections between radiocarbon spikes and other possible supernova events, but we know of supernovae without radiocarbon spikes and spikes without associated supernovae.

Other possible causes include solar superflares, but an flare strong enough to produce the 774 CE radiocarbon spike is unlikely to have erupted from our Sun. Perhaps there is previously unrecorded solar activity. However, the fact of the matter is that there is no simple explanation that explains exactly what causes Miyake events.

And that’s worrying, according to the researchers. The human world has changed dramatically since AD ​​774; A Miyake event could now cause what scientists are calling an “internet apocalypse” by damaging infrastructure, harming the health of air travelers and even depleting the ozone layer.

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

“But we don’t know how to predict it or what damage it can cause. These probabilities are quite alarming and lay the groundwork for further research.”

The research was published in Proceedings of the Royal Society A: Mathematical, physical and technical sciences.