The 38th parallel structures, also known as the 38th parallel lineament, are a series of seven circular depressions or deformations stretching across southern

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...

and

Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...

and into eastern

Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...

, in the United States, at a

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

of roughly 38 degrees north. Estimated at 300 million years old, two are believed to be

impact event An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or me ...

s from meteorites, but other structures are possibly remnants of

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

History

Rampino and Volk (1996) postulated that these structures could be the remains of a serial meteorite strike during the late Mississippian or early Pennsylvanian periods (320 ± 10 Ma).Rampino & Volk, 1996, p.49 Difficulty in determining the age of many of the structures and doubts about the exogenic origins of several of them leave some

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...

s skeptical of this hypothesis. As of 2016, only two of the structures,

Crooked Creek Crooked Creek may refer to: Streams In Australia * Crooked Creek (Clyde River), a tributary of the Clyde River in New South Wales * Crooked Creek (Walsh River), a tributary of the Walsh River in Queensland In the United States * Crooked Cree ...

(320 ± 80 Ma) and Decaturville (< 300 Ma), both in Missouri, are listed as confirmed impact craters in the

Earth Impact Database The Earth Impact Database is a database of confirmed impact structures or craters on Earth. It was initiated in 1955 by the Dominion Observatory, Ottawa, under the direction of Carlyle S. Beals. Since 2001, it has been maintained as a not-for-pr ...

. There is evidence that at least some of the features, such as Hicks Dome in Illinois, are volcanic in origin. These features are associated with faults and fractured rock, and are accompanied by igneous rocks and mineral deposits. Hicks Dome is a structural

dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

which has its central

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

core displaced upward some in relation to the surrounding

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

. The dome has small associated

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

dikes Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...

around its flanks.Raymond Wiggers, 1997, ''Geology underfoot in Illinois'', Mountain Press, p. 252–256. Interest in the possibility of serial impacts on Earth was piqued by observations of

comet Shoemaker–Levy 9 Comet Shoemaker–Levy 9 ( formally designated D/1993 F2) broke apart in July 1992 and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of Solar System objects. This generated a l ...

impacting on

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

in 1994. It has been estimated, however, that the likelihood of such an event occurring 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 serial impacts on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

, whose gravitational field is even weaker, can be seen in several chains of craters on the lunar surface.

History

See also

References

Bibliography

Further reading