By Sophia Dengo, CNN
History books may tell you that in the eighth century, the Moors invaded Spain and Mayan civilization was on the decline, but they don't say anything about the Earth being irradiated.
That event is not documented, but astronomers say a collision in space at that time could have resulted in the high levels of carbon-14 and beryllium-10 found in trees from the eighth century.
Astronomers Valeri Hambaryan and Ralph Neuhauser, based at the Astrophysics Institute of the University of Jena in Germany, published results in the journal Monthly Notices of the Royal Astronomical Society that suggest that two "compact stellar remnants" - which could be neutron stars, black holes or white dwarfs - collided and merged, resulting in a short-duration gamma-ray burst that hit Earth.
Editor's note: Arthur Caplan is the Drs. William F and Virginia Connolly Mitty professor and director of the Division of Bioethics at New York University Langone Medical Center.
(CNN) - So now we know - there won't be a Neanderthal moving into your neighborhood.
Despite a lot of frenzied attention to the intentionally provocative suggestion by a renowned Harvard scientist that new genetic technology makes it possible to splice together a complete set of Neanderthal genes, find an adventurous surrogate mother and use cloning to gin up a Neanderthal baby - it ain't gonna happen anytime soon.
Nor should it. But there are plenty of other things in the works involving genetic engineering that do merit serious ethical discussion at the national and international levels.