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A bolide with a diameter of 10 km and having a chondritic composition would be expected to be totally vaporized upon impact with the terrestrial surface. The uniform global dispersal of the vaporized material of the impactor would result in an areal density of 3 kg/m2 of chondritic fallout diluted 10 to 100 times by terrestrial ejecta. If the bolide has the same composition as the Allende CV carbonaceous chondrite, the areal density of nickel fallout would be 40 grams per square meter at concentration between 1,330 ppm and 133 ppm when mixed with terrestrial ejecta. Because there is about 70 percent chance of a pelagic impact, the combined bolide and terrestrial ejecta fallout would probably have a large component of water. This “rain out” would have a pH in the range of 1 to 2 and would include transition metals, probably in the form of nitrates due to production of nitrogen oxides in the impact fireball. When present at concentrations of >40 ppm, nickel (as soluble salts such as nitrates) will induce chlorosis (the inhibition of chlorophyll production) in plants. Young seedlings developing from seed stocks are particularly susceptible to chlorosis, as demonstrated by experiments involving the subjection of Raphanus sativus (radish) seeds to the soluble fraction of the Allende meteorite, which contains nickel salts. Presumably, mature root stocks are also at risk. This suggests a nickel “coup de grace” to seed and root stocks, severely inhibiting the recovery of terrestrial flora after a 10-km-diameter bolide impact.

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