The Scotia impact is the speculation that the theory of the tectonic evolution of the west Scotia Sea might only be part of the story, and that the entire region might have originally been formed in a cataclismic meteor strike which resmbled a rock, skipping across a calm pond, making deep gouges in the plates as it went, and forever changing the shape of the world.
Evidence for this speculation comes in several forms. First, the recent gravity field measurements made possible by GRACE have yielded a fascinating picture of the region, which tempts the eye toward the assumption of meteoric impact:
This map clearly shows three trails leading west from the area of the South Georgia and the South Sandwich Islands. These three tracks of denser, thicker or otherwise more gravitationally attractive material suggest the path and northern and southern wake of such an event, but it is the final "bulb" that makes up the region of the South Georgia and the South Sandwich Islands which is truly striking. It is almost perfectly circular, unlike the similar semi-circular structure in the Caribbean Sea.
In the topological map:
the rest of the structure can be seen. The truly stunning portion of the structure is the complete lack of any concentric spreading from the southern tip of South America. If this region were created over geologic timeframes by tectonic activity, then the land which is obviously being "pushed" through the plates near South America should be spreading out in a circular pattern. Instead, it looks far more like the wake of a very fast, but small boat, which is circular near the bow, but becomes linear as the boat's path is viewed from farther away. The entire region is a deep scar in the earth, unlike any other structure.
Is this the result of a meteoric impact? I have no idea, but none of the literature that I can find on the Web seems to explain any further than to suggest that significant tectonic activity has taken place (which is certainly true), but that does not preclude such an impact. In fact, such a giant impact would almost certainly result in stress or outright fracturing of the nearby plates, prompting further tectonic activity.
Other possible causes could include:
- The region might be the result of a caldera-forming volcano similar to the Yellowstone Caldera. This would explain the lack of concentric spreading.
- Tectonic movement might have been opposed on the northern and southern sides by differences in materials or density.
- If the plates that carry Antactica and South America were moving westward in roughly the same direction, this sort of imprint might be made, but it is unclear how this would result in the deep trench in the center of the structure.