![]() ![]() ![]() A heat pulse and subsequent fires appear to explain terrestrial species extinctions following the asteroid impact. The K-Pg extinction that followed the Chicxulub impact was one of the five great Phanerozoic marine mass extinctions in terms of both loss of genera and the restructuring of communities. In addition, detrital feeders appear to have had low extinction rates in either marine or freshwater environments, but again freshwater taxa would have been favored by higher renewal rates of detrital organic matter as a result of their direct hydrologic contact with soil. Inland waters, although probably subject to high mortality, showed lower proportionate extinction than marine environments probably because of the greater potential among the freshwater taxa for dormancy, the greater efficiency of reaeration by rapid flow to offset oxygen demand, abundant thermal refugia fed by groundwater at moderate temperatures, and preadaptation of freshwater taxa to a great degree of environmental variability. Other potential causes of mortality in aquatic ecosystems include lower ambient temperatures and anoxia due to the lack of photosynthetic oxygen. Because aquatic ecosystems, unlike terrestrial environments, are strongly dependent on daily photosynthetic output by autotrophs, loss of phytoplankton likely caused catastrophic mortality and extinction in aquatic ecosystems. The resulting cessation of photosynthesis caused a globally extensive extinction of phytoplankton taxa. Extinction in marine environments resulted from the effects of an “impact winter” caused by dust and smoke in the atmosphere that extinguished sunlight at the Earth's surface for a period of months to years. Aquatic environments were shielded from this heat and fire but nevertheless showed massive extinction in marine environments and, for reasons unexplained, far less extinction in freshwater environments. The Chicxulub asteroid impact produced massive extinction in terrestrial environments most likely through an intense heat pulse and subsequent widespread fires. ![]()
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