Free Astronomy Magazine January-February 2018

31 JANUARY-FEBRUARY 2018 EARTH A n outcrop of rock in Arroyo el Mimbral, Tamaulipas, Mexico, is a good example of the complex deposits of impact debris and other sediment produced by the Chicxulub impact event. The lower portion of the sequence (bottom panel) is composed of altered im- pact melt spherules with an in- terbedded sandy limestone, and overlain with a laminated sand- stone. The base of the laminated sandstone contains plant debris, even though these sediments were deposited on the seafloor beneath ~500 meters of water. The upper portion of the sequence (upper panel) is composed of layers of sandstone, siltstone, and mud- stone. The top of the sequence, where the hammer is resting, con- tains anomalously high concentra- tions of the element iridium, which was produced from the vaporized impactor that produced the Chic- xulub crater. [David A. Kring] It is interesting to note that global cooling also led to a sig- nificant drop in precipitation, perhaps a drastic one due to high levels of soot emitted into the stratosphere. Less light, more frost and less water can only have been a devastating mixture that damaged vegeta- tion and the terricolous and aquatic organisms at the base of the food chain. It is easy to understand that a few years of that scenario were enough to annihilate many living species, and in particular the dinosaurs, the cold-blooded animals (or lukewarm, as some studies would have it) then at the top of the food chain. As the same researchers pointed out in a previous work, a mass extinction would have required a global drop in the surface air temperature of about 8-10 °C, a value that may only have been reached if the Chicxulub asteroid had hit an area with a high concentration of hydrocarbons and sulfates. This eventuality is confirmed depths (<100 m) was faster and greater than cooling at greater water depths (e.g., up to 0.5 °C, 2 °C, 4 °C, 7 °C, and 9 °C de- crease in global mean seawater tempera- ture at a 2-m water depth for 20-, 200-, 500-, 1500-, and 2600-Tg BC ejection cases, respectively, within 1–4 years after the im- pact, and within 1 °C cooling at a 600-m water depth for all cases within >10 years).”