14,300 years ago, a solar storm of extraordinary strength hit Earth. Traces of this cosmic event are immortalized in old tree trunks.
The event is extremely rare, but our star sometimes experiences peaks of intense magnetic activity. Scientists have just discovered traces of one of these powerful solar storms that occurred more than fourteen millennia ago!
The Earth was then bombarded by a flood of particles, causing a sudden increase in the levels of carbon-14, a radioactive element, in the atmosphere. This peak in radioactivity was recorded in the wood of the trees growing at that time.
Petrified trees near the Drouzet river. Photo: Cecile Miramont
Scientists from France and the United Kingdom were able to measure this by examining ancient tree trunks. Buried for millennia, they are resurfacing as the Drouzet River in the French Alps erodes its banks. These results were published in the journal Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences.
Édouard Bard, climatologist and lead author of this study, says that these famous trees are close to his house. These are partially petrified pine trunks that have been well preserved over time. “This site is truly extraordinary. We have been working to cut down these trees for over 20 years. They are not whole and have neither leaves nor branches, but the trunk and the stump remain,” emphasizes the researcher from the European Center for Research and Education in Environmental Geosciences (CEREGE) in France. The climatologist states that the trees from this ancient era are very rare and very valuable for research.
If we can travel back in time by studying the growth rings of trees, we can also take the analysis further by looking at the isotope content of each ring. That’s exactly what Édouard Bard’s team did by studying the carbon 14 of fifteen samples of ancient trees. Two of them made it possible to demonstrate an abrupt change 14,300 years ago. “We see a carbon-14 anomaly. There is too much carbon 14 and we see it very clearly by analyzing the tree rings,” says Édouard Bard during a telephone interview with Québec Science. The researcher did not expect such a result. “It was a bit of a surprise, but we knew such an event could be possible,” he adds.
Here we see the rings of a petrified tree. This was found in the Drouzet river. Photo: Cecile Miramont
These results are consistent with an isotope anomaly discovered in ancient Greenland ice cores from the same period. In fact, another dating technique, cosmogenic isotope dating, has shown abnormal concentrations of certain isotopes, including beryllium 10 and chlorine 36. These isotopes “are also influenced by the sun in the short term,” explains the researcher. So scientists have more than one reason to believe that there was an extremely violent solar storm 14,300 years ago.
What impact would it have if a solar storm of this magnitude were to occur again? Édouard Bard, who specializes in geochronology and climate, doesn’t make too many predictions. However, it is certain that there will inevitably be “consequences on the power grid, the Internet network and the communication systems”. That’s why scientists around the world carefully monitor solar activity to predict all possible scenarios.
A chance discovery
While scientists were trying to refine the carbon-14 dating method, they discovered the mega solar storm. Carbon-14 dating is widely used in science, particularly archeology, to determine the age of samples of ancient living organisms. Over the course of their lives, they have integrated atmospheric carbon into their tissues – a mixture of carbon 12 and carbon 14. The latter breaks down over time, one specimen still contains as much carbon 12, but over the years less and less carbon 14. One specimen , which contains little carbon 14, is therefore considered older.
However, when there is strong solar activity, the ratio between carbon 14 and carbon 12 in the atmosphere varies, which can distort the dating of the sample. ” The method [de datation au carbone 14] is based on the assumption that there is a constant level of carbon-14 in the atmosphere. But that’s not true in detail. We see temporal fluctuations in the atmosphere,” explains Édouard Bard. To take this into account, scientists have created a carbon-14 calibration curve based in particular on the study of ancient tree trunks. The ancient logs excavated by the team will allow this curve to be refined, making the dating even more precise.