A tree’s rings mark both its age and the local environmental conditions, which allows researchers to track historical changes in an ecosystem. But tree rings can also encode signals from beyond Earth: Ancient trees in the Northern Hemisphere have preserved a radioactive souvenir from a 1200-year-old burst of cosmic rays.
Using tree rings, researchers have collected 3,000 years worth of data on the presence of the radioactive carbon isotope carbon-14 in the atmosphere. When examining the ebb and flow of carbon-14 over time, Japanese researchers noticed an increase during the 8th and 9th centuries CE. They decided to look at that period in detail by studying the yearly concentrations of carbon-14 in Japanese cedar trees. The cedars revealed a 1.2 percent carbon-14 spike that lasted less than a year between 774 and 775 CE, which corresponded with similar spikes in North American and European trees. This peak, twenty times the amount of variation normally caused by the sun’s fluctuations, resulted from a short-term burst of cosmic rays. But where did those rays come from—a supernova, a solar flare, or some other source?
What’s the News: Large, corral-like stone stone structures found in the Middle East, called desert kites, were used to capture entire herds of gazelle for slaughter 6,000 years ago, suggests a study published online yesterday by the Proceedings of the National Academy of Sciences. While historians and archaeologists have long suspected the structures may have been used to round up and kill gazelles, this study, which found and dated thousands of gazelle bones in close proximity to several desert kites, provides physical evidence to corroborate the idea and an estimate of when the kites were used. (A labeled aerial photo of a desert kite can be found here.)