Since the beginning of history, humans have made note of important astronomical events. This is very useful for allowing archaeologists to date events precisely. And a new discovery now provides researchers with another astronomical tool for archaeology: solar storms.
Archaeologists from the University of Oxford have discovered that the effect of solar storms in the atmosphere can be measured in tree rings, which allow for a more precise estimation of dates. So far two dates of suspected solar storms have been set with this technique, 775 CE and 994 CE, with samples supporting the idea found in Germany, Russia, the US, and New Zealand
The study, published in Proceeding of the Royal Society A, is an extension of carbon dating. Most of the carbon in the world is made of six protons, six neutrons, and six electrons ,but charged particles hitting the atmosphere creates carbon-14 (C-14), which has eight neutrons. Every living creature on Earth has a certain proportion of carbon-14 in its body and C-14 is radioactive.
Once an organism dies, the carbon-cycle stops so the C-14 in its body simply sits there and begins to turn into nitrogen. By measuring the amount of C-14 in a sample, archaeologists can provide a date with an uncertainty of about 50 to 100 years.
During solar storms, the Sun hits Earth with a lot more energetic particles, so the production of C-14 is increased. Plants and trees absorb the C-14 from the atmosphere and this results in tree rings that have at least 20 times more C-14 than usual.
"Variations in atmospheric radiocarbon concentration are largely the result of carbon dioxide emissions from activity from volcanoes and the ocean, but they are also influenced by changes in solar activity,” said lead author Dr Michael Dee in a statement.
“The spikes in 775 and 994 AD were almost vertical and of comparable magnitude all around the Earth. Such markers can be easily identified in known-age tree-rings and are fixed in time.”
This kind of signature could potentially be found in papyrus reed, timber, and other plant materials, and it could allow the syncing of the Mayan calendar to the Gregorian calendar, and make sense of the “floating chronologies” of ancient Egypt.
“In the past, we have had floating estimates of when things may have happened, but these secret clocks could reset chronologies concerning important world civilisations with the potential to date events that happened many thousands of years ago to the exact year," Dee said.