Free Astronomy Magazine January-February 2018

28 JANUARY-FEBRUARY 2018 EARTH A rtist's recon- struction of Chicxulub crater soon after im- pact, 66 million years ago. [Detlev Van Ravenswaay/Sci- ence Source] On the side, Lift- boat Myrtle is a drilling platform normally used for oil operations. Since April 2016, geologists have been using it in the Gulf of Mex- ico to drill into the crater Chicxu- lub. [ELeBer/ ECORD/ IODP] significantly reduced temperatures long enough to cause a mass extinction. The soot must, therefore, have been in the stratosphere (where it could have persisted for years), and only the soot produced and ejected as a direct result of the impact could have gotten so high. By studying this aspect of the Chicxulub event through a series of computer simu- lations, Kaiho and Oshima discovered that the asteroid, to transfer the necessary quantity of elements in suspension into the stratosphere, must have hit sedimen- tary rocks particularly rich in hydrocarbons and sulfates. By burning at the very high temperature produced by the impact, these elements turned into soot and aerosols. The most surprising aspect is that only about 13% of the Earth’s surface con- tains rocks with that composition, and only by striking those areas could the as- teroid have produced a mass extinction. In other words, if the asteroid had fallen any- where in the remaining 87% of the Earth’s surface, the effects on the biosphere would have been devastating over a re- gion or, at most, a continent, and the di- nosaurs would not have died out. In this case, the evolution of life on Earth would