T67 Impact Cratering: A Dominant Process in the Solar System

Sunday, 22 September 2024
1:30 PM - 5:30 PM
213A

THE PRESSING PROBLEMS OF PROVING (AND DISPROVING) VERY RECENT IMPACT EVENTS IN THE GEOLOGICAL RECORD

Paper number: T67-2
Program: Technical Sessions
Time: 1:35 PM – 1:55 PM

Authors

Abstract

Nothing captures the imagination quite like stories of murder, mystery, and intrigue, with the possible exception of invaders from space. Put those ingredients together and you have the makings of a blockbuster novel or an incredibly compelling scientific paper. The latter presumes, of course, that you have observable, reproducible evidence of a moment when space met man, whether that be in the form of hypervelocity impacts, radiation from exploding stars, or things yet to be conceived. Logically, these encounters must have occurred, and more than once, in the several million years our ancestors have inhabited Earth. But short of live video, how do we demonstrate that these events have happened, and even separate ancient myth from physical fact?

If we conclude, based on recent history, that such catastrophes are exceptionally rare, when we now know, for instance, that the flux of asteroid impacts in the distant past episodically increases, we are left to question why even bother investigating the geologic record. Clearly, we need to be able to reliably identify such recent events.

But the fundamental problem of studying the recent record of asteroid and comet collisions is stated bluntly: Mankind can make (almost) anything!

We have made shocked minerals and microtektites in nuclear blasts.

We have made UHT mineral phases and melt glasses, even in antiquity. For example, in the interior of Bangladesh, we investigated an extensive layered deposit of tektite-like glass that is dry, nearly free of crystallites, and which contains high-temperature spinel and ballen silica. Had deeply buried kilns not eventually been excavated, we easily could have defended a hypothesis for a c. 800-year-old impact in the region.

And anthropogenic materials that mimic cosmic debris are not limited to the surface. We are conducting a controlled experiment to measure the rate of infiltration of industrial fly ash through Upper Coastal Plain sediments, like those where many Younger Dryas impact makers have been claimed. Some data suggest that through a combination of agricultural processes and bioturbation objects may go down many meters.

An additional complication with surficial sediments is that they potentially condense the impact record of large intervals of geologic time. Care must be taken to account for ancient ejecta coincidentally incorporated into recent soils and anthropogenic materials.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-404353

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