The Impact Record Is Not Uniformly Distributed Through Time - It Clusters Into Bombardment Epochs

The assumption built into most public discussion of impact risk is that the threat is randomly distributed - that any given century is about as dangerous as any other, and that the absence of a major impact in recent memory is simply the normal background state. Randall Carlson argues the geological record does not support that assumption.

The impact record, when examined across deep time, does not appear uniform. It clusters. There appear to be periods - bombardment epochs - during which impact frequency increases significantly, driven by the fragmentation of a large parent body into multiple offspring that then litter the inner solar system, particularly the plane of the ecliptic where Earth's orbit is located. Each fragment becomes an independent impactor. Each impactor can itself degrade into smaller objects and debris streams. The result is an extended period of elevated impact probability that can persist for thousands of years before the debris disperses sufficiently to return to background levels.

The Younger Dryas boundary is Randall's primary example of what a bombardment epoch looks like in the geological record - and the Taurid complex, the debris field of a giant comet that has been fragmenting for tens of thousands of years and that Earth crosses twice annually, raises the question of whether the current era represents the tail end of one such epoch or the beginning of another.