NASA Scientists Classify the Time Before Earth Existed: the Chaotian Era
The geological time scale, with its familiar Cretaceous, Cambrian, and Eocene periods, works great as a calendar for the history of the Earth. Indeed, the different periods only cover the 3.8 billion years of life on Earth, with everything before that time lumped into one nondescript eon called the Hadean. But for some geologists, that lack of specificity simply won't work any more. Frustrated by referring to Hadean-era events with vague phrases like "around the time of Moon formation" or "shortly after Earth cooled", four scientists, including two from NASA, have chopped up the Hadean into distinct geologic periods, and even extended the time scale back to the formation of the solar system, with a new eon called the "Chaotian." Under the new scheme, the Hadean Eon begins when Tellus, the proto-Earth, gets smacked into by Theia, a proto-planet absorbed into the Earth. This impact caused the formation of the Moon,...