Image: When the sun emits solar flares, intense activity increases radioactivity in the atmosphere which is detected in tree-rings, NASA
Until now scholars have had only vague evidence for dating when events happened during the earliest periods of civilisation, with estimates being within hundreds of years. However, the unusually high levels of the radioactive isotope carbon-14 found in tree-rings laid down during the radiation bursts could help reliably pinpoint dates. The distinct spikes act as time-markers like secret clocks contained in timber, papyri, baskets made from living plants or other organic materials, says the paper published in the Royal Society Journal Proceedings A.
Scholars believe that intense solar storms caused major bursts of radiation to strike the Earth in 775 and 994AD, which resulted in distinct spikes in the concentration of radiocarbon in trees growing at that time. The dates of historical events can be nailed precisely because the tree-rings belong to archives in which the growth year of each tree-ring is exactly known. The Oxford authors outline how they could detect similar spikes elsewhere within the thousands of years of available tree-ring material from across the world, saying even a handful of these time-markers could allow them to piece together a reliable dating framework for important civilisations.