38th parallel structures

The 38th parallel structures are a series of circular depressions or deformations stretching 700 km (435 mi) across southern Illinois and Missouri into eastern Kansas at a latitude of roughly 38 degrees north. Rampino and Volk (1996) postulated that these could be the remains of a serial meteorite strike in the late Mississippian or early Pennsylvanian periods. Difficulty in determining the age of many of the structures and doubts about the exogenic origins of several of them leave some geologists sceptical of this hypothesis.

Interest in the possibility of serial impacts on Earth was piqued by observations of comet Shoemaker-Levy 9 impacting on Jupiter in 1994. It is estimated, however, that the likelihood of such an event on Earth is vanishingly small because the Earth's weaker gravitational field is much less able than Jupiter's to pull a speeding object close enough to be torn apart by tidal forces. However, evidence of past serial impacts on the Moon can be seen in several chains of craters.

See also

• Impact event
• Roche limit

References

• Rampino, M.R, and T. Volk. 1996. Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids?. Geophys. Res. Lett. 23, 49–52. (Abstract)
• Evans, Kevin R.; Mickus, Kevin L.; & Rovey, Charles W. III (2003). The Weaubleau Structure: Evidence of a Mississippian Meteorite Impact in Southwestern Missouri. Association of Missouri Geologists Field Trip Guidebook, 50th Annual Meeting. Missouri Department of Natural Resources. PDF
• Luczaj, J. 1998. Argument supporting explosive igneous activity for the origin of "cryptoexplosion" structures in the midcontinent, United States. Geology 26(April):295.
• Richard Monastersky (2001). Target Earth – Geologists Link Chain Of Huge Impact Craters. Retrieved November 27, 2004.