As trees grow outward year by year, they preserve a great deal of information in their inner rings, which scientists have used to study a variety of phenomena in the distant past. The latest purpose of tree ring analysis, along the banks of the Drouzet River in the French Alps, is an extremely powerful solar storm that hit the Earth 14,300 years ago.
Radiocarbon analysis yielded the find, which showed a dramatic spike in carbon-14, a radioactive isotope of carbon used to date objects from the past, in tree rings that corresponded to that time period. The isotope exists naturally in small numbers, but can be created by sudden bursts of electromagnetic rays from the sun, such as those flung at the Earth by the sun when it releases large solar flares.
The trees studied were not alive, of course, but weren't fossilized, either. They existed in a state of semi-fossilization, with their organic molecules partially replaced by stone.
A paper describing the discovery by a group of French and British scientists was published on Monday in The Royal Society’s Philosophical Transactions A: Mathematical, Physical and Engineering Sciences.
“Radiocarbon is constantly being produced in the upper atmosphere through a chain of reactions initiated by cosmic rays,” said Edouard Bard, professor of Climate and Ocean Evolution at the Collège de France and CEREGE, and lead author of the study, in a statement.
“Recently, scientists have found that extreme solar events including solar flares and coronal mass ejections can also create short-term bursts of energetic particles which are preserved as huge spikes in radiocarbon production occurring over the course of just a single year.”
The storm 14,300 years ago is the largest known to have occurred over the last 15,000 years. Previously, nine other storms of similar size - known as Miyake Events - were known about, with the largest happening in 993 CE and 774 CE. However, this newly identified storm was at least twice as powerful as them.
The study of such events helps scientists understand solar activity before the 18th century, when sun spots - the producers of solar flares - first began being observed by human scientists. It is also important because in our modern, electricity-driven society, large solar storms have the potential to wreak havoc by disabling electrical systems and computers.