g-rh@cca.UUCP (04/11/87)
Enquiring minds want to know mechanisms were supposedly involved in the Cretaceous mass extinction event. The following is a summary drawn from "The Great Dying", previously mentioned on the net. THE EVENT A meteorite hits the Earth. It may have been an Apollo object (solid, rocky or metallic, asteroid) or a comet head (big ice ball with lots of gravel). Size of the meteorite was on the order of 10 kilometers diameter. Mass on the order of a trillion (10^12) metric tons. Impact speed 15-40 kilometers per second. Energy of impact 200 million megatons of TNT. Mortality patterns imply that the strike was in the Northern hemisphere spring, probably in April. The strike was probably in the Northern hemisphere. IMMEDIATE EFFECTS If it was a water strike about 5000 cubic kilometers of water was injected into the atmosphere. In any case most of the energy of impact is taken up by the surface (land or ocean bottom). The impact crater was about 200 kilometers diameter. A large amount of extraterrestrial material was distributed world wide. About a billion tons of NO molecules were generated from the impact. Dust and cloud cover create total darkness for about two months. The ozone layer is wiped out for a period of 1-10 years. There are world wide forest fires. Acid rain (NO molecules rapidly oxidize to form NO2, NO3, and nitrous and nitric acid in turn) wipes out most of the ocean one celled life. This is augmented by darkness (for the northern hemispher particularly) and run off from decaying dead biota in the land masses. CO2 levels rise sharply (drastically less plant life) with a green house effect that brings the average temperature up about 5 degree centigrade. RECOVERY The recovery period runs about 50000 years. Plant life recovers in about 2000 years. Rain flushes the acid waters into the ocean where there are in turn neutralized by lime deposits. There is strong selection for plankton species that can thrive in acidic water. In the initial recovery period plant life is dominated by plants which propogate by air born spores (e.g. ferns) with the flowering plants making a later recovery and resuming their dominance. Many species die out during the massive mortality of the event itself and the immediate aftermath. A substantial number of species that were typically cretaceous died out in the recovery period. The typically tertiary species multiply rapidly and by the end of the recovery period occupy all of the new niches. Temperatures drop substantially during the recovery period once the CO2 surplus is mopped up by recovering plant life. Extinction of the remaining cretaceous species occurs because of the heavy environmental stresses and because of the drastically altered ecology. The new tertiary species are descendents of minor species that were better qualified to survive under the hard times of the event and the early recovery period. -- Richard Harter, SMDS Inc. [Disclaimers not permitted by company policy.]