Impact of an asteroid or comet in the ocean and extinction of terrestrial life

Abstract

Finite difference calculations describing the impact mechanics associated with a 10 to 30 km diameter silicate or water object impacting a 5 km deep ocean overlying a silicate solid planet at 30 km/sec demonstrate that from 12 to 15% of the bolide energy resides in the water. In the gravity field of the earth some 10 to 30 times the impactor mass of water is launched on trajectories which would take it to altitudes of 10 km or higher. This ejecta launched on trajectories which can achieve stratospheric heights is 10^1 to 10^2 projectile masses, similar to that resulting from impact of objects on an ocean‐free silicate half‐space (continent). As in the case of impact directly onto a continent, only the ejecta composed of impactor material, launched on trajectories which would carry it to stratospheric heights, matches the fraction (10^(−2) to 10^(−1)) of bolide (extraterrestrial) material found in the platinum‐metal‐rich Cretaceous‐Tertiary and Eocene‐Oligocene boundary layers. Oceanic impact results in impulsivelike giant tsunamis initially having amplitudes of ∼4 km, representing the solitary waterwave stability limit in the deep ocean, and containing 10^(−2) to 10^(−1) of the energy of the impact. Using the constraint of no observed turbidites in marine sediments in the Cretaceous‐Tertiary and Eocene‐Oligocene boundary materials (calculated maximum water‐sediment interface particle velocity ∼10° m/sec) implies a maximum impactor energy of ∼10^(28) to ∼10^(29) erg corresponding to a maximum diameter for a silicate impactor of ∼2 km (at 11 km/sec). Minimal global tsunami run‐up heights on the continents corresponding to impacts of this energy are 300–400 m. We speculate that such waves would inundate all low altitude continental areas and strip and silt over virtually all vegetation. As a result, the terrestrial animal food chain would be seriously perturbed. This, in turn, could have caused extinction of large terrestrial animals including the archosaurs.

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