September Presentation: Impacts Great and Small—The Role of Hypervelocity Collisions in Sculpting Earth’s Geology

When: 6:45pm, September 28

The meeting will be offered in hybrid format—live at the Fernbank Museum and via webcast. To obtain webcast link contact [email protected]

Abstract: Only since the confirmation of shocked mineral phases at Barringer (Meteor) Crater by USGS geologists Gene Shoemaker and Ed Chao in the late 1950s has impact cratering by hypervelocity collisions with asteroids and comets been considered a significant agent of geologic change on the surface of Earth– despite having been recognized as the most ubiquitous source of upheaval on other solid planets decades before. Today the scars of approximately 200 impacts have been recognized in the Earth’s crust ranging in size from 10s of meters to more than 200 kilometers in diameter and in age from 14 years to 2.2 billion Ga. Dozens of deposits of ejecta have been identified throughout the stratigraphic record, a few well-correlated with impact structures and some apparently the only surviving remains of events both large and small, including a few likely produced by air bursts just above the ground.

Although spacecraft missions have only increased our understanding of the importance of impact cratering throughout the solar system, and the potential cataclysmic effects on life have been popularized by the K-Pg mass extinction; impact cratering still is unappreciated as a fundamental process responsible for sculpting the evolution of the Earth’s lithosphere at many scales. When many people imagine impacts, they likely think of Barringer Crater, which somewhat like our Sun to astronomers is easily accessible, instructive, and aesthetically pleasing but probably isn’t all that representative of the phenomenon. Thanks to the Carancas impact in Peru in 2007, we must look at every small pock mark across a barren plain with a more critical eye.  And the other end of the spectrum, large impacts can produce enormous volumes of igneous rocks, large-scale tectonic deformation, and thick sedimentary deposits that can be and often have been interpreted as representing millions of years of geologic history– before geologists stumbled upon the evidence that everything had formed almost in the blink of an eye. We will examine the record of asteroid and comet impacts on Earth and what it means for understanding the geologic past of our planet.

Speaker Bio:  R. Scott Harris is the planetary geologist and meteorite curator for Fernbank Science Center and the Jim Cherry Memorial Planetarium in Atlanta, Georgia. A Georgia native, he was educated at Arizona State University, the University of Georgia, and Brown University. A world traveler, field geologist, petrologist, and educator, he has spent most of his 30-year career studying the record of asteroid and comet impacts on Earth. The author or co-author of more than fifteen peer-reviewed papers and field guides and over a hundred conference abstracts, Scott also studies extraterrestrial volcanism and the ancient history of our solar system preserved in meteorites.  He is the current Outstanding Earth Science Teacher for Georgia, awarded by the National Association of Geoscience Teachers, and serves as Communication Director for the Southeastern Section of NAGT. Scott also serves as the new Field Trip Coordinator for AGS.