Power outages, broken satellites, high levels of radiation during air travel: If a massive solar storm were to occur today, the resulting local change in the earth’s magnetic field would have serious consequences.
A study conducted by a team led by climate scientist Edouard Bard from the University of Aix-Marseille shows that this could certainly happen recently in the specialist journal Philosophical Transactions of the Royal Society A published. Accordingly, 14,300 years ago a solar storm of previously unknown proportions raged on Earth. The researchers discovered this by studying the annual rings of subfossil trees using the radiocarbon method. They noticed abnormalities in certain rings: in a single year, the proportion of radioactive carbon atoms rose sharply – and then fell again. For the study authors, this is due to a devastating solar storm.
Radiocarbon, the radioactive carbon isotope C-14, is continuously produced in the upper atmosphere through a series of reactions emanating from cosmic rays. In living organisms, carbon accumulates uniformly, but in dead organisms the proportion of C-14 atoms decreases over time compared to C-12, the most common carbon isotope. This decay always occurs at the same rate, which is what radiocarbon dating is based on. Extreme solar flares can lead to the accumulation of additional C-14 if the energetic particles spewed out by the sun reach the Earth.
The research group detected traces of such an event in the trees examined. A total of 111 subfossil tree trunks were included in the analysis; they had first uncovered the trunks using a pickaxe on the banks of the Drouzet river in the southern French Alps. “Subfossil” means that the process of fossilization is not yet complete, but the dead wood is largely preserved. Every year subfossil trees are exposed through erosion in the upper reaches of the Durance and its tributaries.
Solar flares are currently becoming more common
The research group first cut slices out of the preserved Scots pines using a chainsaw. The slices were then taken to the laboratory, where each tree was sorted along a timeline through dendrochronological analysis. Dendrochronology is the science of determining the age of trees. In the simplest case, this is done by counting the annual rings. However, wooden rings reveal much more about trees, such as climatic changes.
In the laboratory, the researchers separated a strip from some of the wooden discs. The strips were divided into small pieces of wood weighing 100 milligrams using a scalpel, so that each piece corresponded to a growth ring. The researchers then analyzed more than 400 pieces of wood from 15 different trees using the radiocarbon method, with the result that the C-14 concentration increased by around 30 percent 14,300 years ago – a relic of the strongest solar storm known to date. This measurement was confirmed in a comparison with anomalies in the isotope abundance of beryllium-10 in ice cores from Greenland.
But what is the probability that such a solar storm will occur again? The northern lights that were recently seen in Germany are an indication that solar activity, which fluctuates in an eleven-year cycle, is currently increasing. That’s why solar flares, the ejection of charged particles, which then fly through space in a plasma cloud and can trigger a solar storm when they impact the Earth’s atmosphere, are currently occurring more frequently. However, the plasma clouds are thrown radially in all spatial directions; the earth only makes up a tiny part of the possible target area. The probability of a catastrophic solar storm like 14,300 years ago is therefore low.
For the people of the Upper Paleolithic, the massive solar storm probably had a mild outcome anyway. They probably saw apparitions of light; However, the atmosphere and the earth’s magnetic field offer protection from damage to health on the ground.