Detection and significance of mass killings

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Abstract
Mass killings that appear to be approximately synchronous and involve total disappearance of biomass at a bedding plane in many independent sections globally suggest a common cause and therefore synchroneity. Diversity changes and taxa plots are of dubious value in detecting extinctions and cannot identify an event horizon with any precision. Less common taxa often show a gradual decline before any arbitrary horizon. Survivors after a major biomass disappearance are not uncommon. Such mass killings identify an horizon which may then be examined for evidence of cause. Geochemical markers may be ephemeral and absence may not be significant Highly energetic bolide impacts occur and their flux is known. Large paroxysmal volcanic events may also occur over a relatively short time interval (ca. 1/2 Ma). Large events must leave a trace: biotic geochemicai and sedimen to logical. There appears to be no reason why ongoing phenomena such as climate and sea‐level changes are primary causes of anomalous episodic extinctions.