The world’s attention turned to the skies over Georgia on June 26, 202, as a bright fireball exploded south of Atlanta and rained down stony meteorites just west of McDonough. I had the opportunity to classify and study the dynamics of one piece that impacted the floor of a residence. The L 5/6 ordinary chondrite, just a few centimeters in diameter, appears to have maintained a significant portion of its horizontal velocity after atmospheric breakup and transited the living room at a speed around 800 m/s. This was the third L ordinary chondrite to drop meteorites in Georgis within the last 15 years.

But those are just the latest in a long history of cosmic collisions that are recorded in the historic and geologic records of Georgia. In addition to 7 documented meteorite falls and 20 finds, the state contains ejecta from the 35.5 Ma Chesapeake Bay impact and a slightly older impact (c. 37 Ma) for which no crater presently is known. I briefly will review my work discovering and characterizing those strata in the Upper Coastal Plain, and I will discuss the consequences of the 66 Ma Chicxulub impact on state’s geology.

But no hypervelocity impact has left such a large and lasting mark on Georgia as the asteroid or comet collision that excavated the nearly 300-kilometer diameter Roosevelt impact structure. What began almost 20 years ago as an intriguing question about a crater-like depression just several kilometers across has culminated in the mapping of a gigantic astrobleme covering 20% of the state. My colleagues and I have identified a variety of shocked-quartz-bearing melt facies, breccias, and spherule beds. The distribution of impact deposits and deformation was found to be consistent with COCORP seismic reflection profile data. These data then were used successfully to predict the locations of additional facies, including meta-geyserites in a large hydrothermal network.

Presently our calculations show that an impactor more than 30 kilometers across, with a trajectory about 15⁰ above the horizon from the present-day ENE, made first contact between Monroe and Meriwether Counties approximately 810 Ma. The original structure would have extended from near Athens, Georgia to Auburn, Alabama, and from north of Atlanta to Albany. The ancient collision possibly occurred as part of a bombardment in the inner solar system that produced a number of large craters on the Moon, including the 93-km Copernicus. And it may be associated with the extinction of cyanobacteria leading to the Bitter Springs Negative 13C Anomaly that also is dated to 810 Ma.

*Refreshments: 12-12:30 PM, ES&T Atrium