38th parallel structures
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The 38th parallel structures, also known as the 38th parallel lineament, are a series of circular depressions or deformations stretching 700 km (435 mi) across southern Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
and Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
into eastern Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
at a latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
of roughly 38 degrees north
38th parallel north
The 38th parallel north is a circle of latitude that is 38 degrees north of the Earth's equatorial plane. It crosses Europe, the Mediterranean Sea, Asia, the Pacific Ocean, North America, and the Atlantic Ocean...
.
Rampino and Volk (1996) postulated that these structures could be the remains of a serial meteorite strike in the late Mississippian or early Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
periods. Difficulty in determining the age of many of the structures and doubts about the exogenic origins of several of them leave some geologists
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
skeptical of this hypothesis. As of May, 2009, only two of the structures, Decaturville
Decaturville crater
The Decaturville crater, also referred to as the Decaturville Dome, is an impact crater in Missouri, United States, and is one of the 38th parallel structures....
and Crooked Creek
Crooked Creek crater
Crooked Creek is an impact crater in Crawford County, Missouri, United States.It is 7 km in diameter and the age is estimated to be 320 ± 80 million years . The crater is exposed to the surface....
, are listed as confirmed in the Earth Impact Database
Earth Impact Database
The Earth Impact Database is the authoritative source for information on confirmed impact structures or craters on Earth. It was initiated in 1955 by the Dominion Observatory, Ottawa, under the direction of Dr. Carlyle S. Beals...
.
There is evidence that at least some of them, such as Hicks Dome, are volcanic in origin. They are associated with faults and fractured rock, and are accompanied by igneous rocks and mineral deposits. Hicks Dome is a structural dome
Dome (geology)
In structural geology, a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval...
which has its central Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
core displaced upward some 4,000 feet in relation to the surrounding strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
. The dome has small associated igneous dikes
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
around its flanks.
Interest in the possibility of serial impacts on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
was piqued by observations of comet Shoemaker-Levy 9
Comet Shoemaker-Levy 9
Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...
impacting on Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
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 serial impacts on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
can be seen in several chains of craters.