IAAG(eologist) -- or at least a lapsed one (seriously, it's really really boring!) -- as far as I'm aware iridium spikes as found at the KT boundary (the event that is hypothesised to have wiped out the dinosaurs) are indicative of meteoritic impact. Chondritic meteorites (the ones that have been around since the birth of the solar system) are rich in a number of unusual elements, iridium amongst them. Comets, on the other hand, are often just balls of ice and dust.
A comet would a) be more likely to airburst (poorer structural integrity) and b) leave no or little elemental anomalies behind.
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IAAG(eologist) -- or at least a lapsed one (seriously, it's really really boring!) -- as far as I'm aware iridium spikes as found at the KT boundary (the event that is hypothesised to have wiped out the dinosaurs) are indicative of meteoritic impact. Chondritic meteorites (the ones that have been around since the birth of the solar system) are rich in a number of unusual elements, iridium amongst them. Comets, on the other hand, are often just balls of ice and dust.
A comet would a) be more likely to airburst (poorer structural integrity) and b) leave no or little elemental anomalies behind.