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24 April 2014 11:45 am ,
Vol. 344 ,
Major climate data sets have underestimated the rate of global warming in the last 15 years owing largely to poor data...
The tsetse fly is best known as the vector for the trypanosome parasites that cause sleeping sickness and a disease in...
The National Institutes of Health is revising its "two strikes" rule, which allowed researchers only one chance to...
By stabilizing the components of retromers, molecular complexes that act like recycling bins in cells, a recently...
Fossil fuels power modern society by generating heat, but much of that heat is wasted. Semiconductor devices called...
Researchers are gaining insights into what made Supertyphoon Haiyan so powerful and devastating through post-storm...
Millions around the world got a first-hand look at what it was like to be in Tacloban while it was pummeled by...
- 24 April 2014 11:45 am , Vol. 344 , #6182
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ScienceShot: What Struck Earth in 775?
3 June 2012 1:00 pm
In 775 C.E., while Charlemagne was ruling his Frankish kingdom, something mysterious struck Earth. An analysis of the rings of two Japanese cedar trees (typical tree rings shown above), reported online today in Nature, reveals that from 774 to 775 C.E., the atmospheric level of radioactive carbon-14 jumped by 1.2%. This indicates that cosmic rays—high-speed, charged particles from space—bombarded our planet and converted some atmospheric nitrogen-14 into carbon-14. Earlier work had found a rise in radioactive carbon during the same decade; the new discovery means that scientists have been able to narrow down the date of impact to within just 1 year. The scientists argue against two logical suspects: solar flares are too weak to do the job, and no supernova explosion was seen at the time, nor do any nearby supernova remnants date back to Charlemagne's time. There's also nothing unusual in the history books. So the cause remains a mystery, but whatever it was, something similar could presumably strike again.
See more ScienceShots.