Eighth century carbon spike not from comet impact

comet impact with earth illustration

A large comet impact, as this artist's impression shows, could not have caused the carbon-14 spike that occurred around A.D. 775.

Don Davis/NASA

Around 775, Earth’s atmosphere experienced a jolt in carbon levels. Scientists proposed that the extra carbon-14, which occurs naturally in trace amounts in the atmosphere, could have come from an outburst of energetic particles from the sun or other stars.

A team of scientists suggested January 16 in Scientific Reports that the increased carbon could have come from a comet impact. But new calculations of the size and mass of such a comet show that the space rock would have been 100 kilometers across and 100 billion to 1,000 billion tons.

An impact of a rock of that size would have been disastrous for the planet and would have left more evidence in geological and written records, argue the authors of a paper posted January 23 on arXiv.org.

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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