Tektites are natural
glassGlass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
rocks up to a few centimeters in size, which most scientists argue were formed by the
impactAn impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
of large
meteoriteA meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s on
EarthEarth 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...
's surface. Tektites are typically black or olive-green, and their shape varies from rounded to irregular.
Tektites are among the "driest" rocks, with an average water content of 0.005%. This is very unusual, as most if not all of the craters where tektites may have formed were underwater before impact. Also, partially melted
zirconZircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
s have been discovered inside a handful of tektites. This, along with the water content, suggests that the tektites were formed under phenomenal temperature and pressure not normally found on the surface of the Earth.
Terrestrial impact theory
The terrestrial-impact theory states that a meteorite impact melts material from the Earth's surface and catapults it up to several hundred kilometers away from the impact site, which means that it must have travelled through space (thus explaining the dryness). The molten material cools and solidifies to glass. According to this theory, a meteorite impact causes their formation, but the precursor material of tektites is primarily of terrestrial origin, as determined from isotopic measurements. Today, the terrestrial origin of tektites is widely accepted based on the results of many geochemical and isotopic studies, e.g. Faul, H.(1966) and Koeberl, C.(1990).
The impact theory relies on the observation that tektites cannot be found in most places on Earth's surface. They are only found in four strewnfields, three of which are associated with known
impact craterIn the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s. Only the largest and geologically youngest tektite deposit in
Southeast AsiaSoutheast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, called the
Australasian strewnfieldThe Australasian strewnfield, covering at least one-tenth of the Earth's surface, is the largest and the youngest of the tektite strewnfields. The 800,000 year-old strewnfield includes most of Southeast Asia...
, has not been definitively linked to an impact site, probably because even very large impact structures are often not easy to detect. For example, since the
Chesapeake Bay impact craterThe Chesapeake Bay impact crater was formed by a bolide that impacted the eastern shore of North America about 35 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" or marine impact craters, and the largest known impact crater in the U.S...
(today the largest known impact structure of the United States and associated with the North American tektite strewnfield) is covered by sediments, it was not detected until the early 1990s. Also, the bigger the strewnfield, the bigger the area to search for the crater. Since several new craters are identified every year, this is not really regarded as a problem by proponents of the tektite impact theory, except for the expected Australasian crater, a feature that would be less than a million years old and thus easily visible. This crater, if it exists at all, has not been located, but there are some candidates
(
Stecher, O.; Storey, M.; Hopper, J. R. Australasian tektites: source parameters and crater location reviewed,
Yung-Tan Lee, Ren-Yi Huang, et. al Geochemistry of Tektites from Hainan Island and Northeast Thailand).
The ages of tektites from the four strewnfields have been determined using
radiometric datingRadiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
methods. The age of
moldaviteMoldavite is an olive-green or dull greenish vitreous substance possibly formed by a meteorite impact. It is one kind of tektite. It was named by A. Dufrnoy for the town of Moldauthein in Bohemia , where it occurs...
s, a type of tektite found in
Czech RepublicThe Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
, was determined to be 14 million years, which agrees well with the age determined for the
Nördlinger RiesThe Nördlinger Ries is a large circular depression in western Bavaria, Germany, located north of the Danube in the district of Donau-Ries. The city of Nördlingen is located about southwest of the centre of the depression....
crater (a few hundred kilometers away in Germany) by radiometric dating of
SueviteSuevite is a rock consisting partly of melted material, typically forming a breccia containing glass and crystal or lithic fragments, formed during an impact event...
(an impact
brecciaBreccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
found at the crater). Similar agreements exist between tektites from the North American strewnfield and the Chesapeake Bay impact crater and between tektites from the Ivory Coast strewnfield and the Lake Bosumtwi-Crater.
Below are some types of tektites, grouped according to the four known strewnfields, and their associated craters:
- European strewnfield (Nördlinger Ries
The Nördlinger Ries is a large circular depression in western Bavaria, Germany, located north of the Danube in the district of Donau-Ries. The city of Nördlingen is located about southwest of the centre of the depression....
, GermanyGermany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, age: 15 million years):
- Moldavite
Moldavite is an olive-green or dull greenish vitreous substance possibly formed by a meteorite impact. It is one kind of tektite. It was named by A. Dufrnoy for the town of Moldauthein in Bohemia , where it occurs...
s (Czech Republic, green)
- Australasian strewnfield (no associated crater identified; but see Wilkes Land crater
Wilkes Land crater is an informal term that may apply to two separate cases of conjectured giant impact craters hidden beneath the ice cap of Wilkes Land, East Antarctica...
and above references):
- Australite
Australites are tektites found in Australia. They are mostly dark or black, and have shapes including discs and bowls that are not seen in other tektites...
s (AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, dark, mostly black)
- Indochinite
Indochinite Tektites are solidified rock, which was fired into the Earth's upper atmosphere by a meteorite impact and subsequently cooled to form the distinctive glass-like structure. Indochinite Tektites are distinctly dark black in contrast to the green of European Moldavite Tektites. It is...
s (South East Asia, dark, mostly black)
- Chinites (China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, black)
- North American strewnfield (Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...
impact craterThe Chesapeake Bay impact crater was formed by a bolide that impacted the eastern shore of North America about 35 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" or marine impact craters, and the largest known impact crater in the U.S...
, USA, age: 34 million years):
- Bediasite
Bediasite is a form or type of tektite. It originates in an area in the eastern part of the U.S. state of Texas centered around the small town of Bedias which is north west of Houston. They are found in about nine Texas Counties in an area of over . The largest specimen ever found is just over...
s (USA, Texas, black)
- Georgiaite
Georgiaite is a form or type of tektite. They are found in part of the 34-million-year-old North American strewnfield coming from the Chesapeake Bay impact crater...
s (USA, Georgia, green)
- Ivory Coast strewnfield (Lake Bosumtwi
Lake Bosumtwi , situated within an ancient meteorite impact crater, is approximately 8 km across and the only natural lake in Ghana. It is situated about 30 km south-east of Kumasi and is a popular recreational area. There are about 30 villages near the lake, with a combined population of...
Crater, Ghana, age: 1 million years):
- Ivorites (Ivory Coast, black)
Early nonterrestrial impact theories
Though the meteorite impact theory of tektite formation is widely accepted, minority theories propose alternate ideas of tektite formation.
Tektites contain no cosmogenic noble gases produced by cosmic rays, a factor that excludes long travel in space, necessary if tektites are not terrestrial. According to terrestrial-impact adherents, this makes a
lunarThe 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...
origin unlikely, because it is hard to reconcile with finding cosmogenic noble gases in all
lunar meteoriteA Lunar meteorite is a meteorite that is known to have originated on the Moon.-Discovery:In January 1982, John Schutt, leading an expedition in Antarctica for the ANSMET program, found a meteorite that he recognized to be unusual...
s – a typical lunar meteorite taking about 1 million years to transfer from Moon to Earth. Furthermore, an origin from the Moon or other body cannot explain why many tektites are only found in confined areas unlike meteorites of lunar or other origin, which are found dispersed on the Earth's surface. Whether the Australasian and Ivory Coast tektites fit this thesis is debatable.
According to researchers, measurements of high concentrations of the
radionuclideA radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
10BeBeryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...
in tektites from the relatively young Australasian strewnfield are an indication of terrestrial origin.
10Be is produced by cosmic rays in the atmosphere, where it is down-washed by rain and incorporated into young sediment layers. Because
10Be decays with a half-life of about 1.5 million years, its concentration in older sediments and other kinds of rocks appears successively lower.
10Be is found in meteorites and lunar rocks at a concentration lower than that of the young sediments because the cosmic rays interact with these rocks to produce much smaller quantities. Many regard these findings as the final breakthrough for the nonterrestrial impact theory, because they show that the precursor material is mainly terrestrial in origin (mixed with small traces of extraterrestrial material, perhaps that of the impactor).
Scientists who claim tektite glasses are impact melts generally ignore their structure (petrography) and high quality. Instead, they base their claims on comparisons of tektite chemistries with the averages of certain sediments, and on certain rare-earth and isotopic values claimed not to exist in the Moon. Other researchers, however, have shown that tektite glasses are not really comparable to terrestrial sediments, which have a wide range of chemical variance – especially in the alkalis; and instead often exhibit igneous (volcanic) chemical trends. They also argue the physical impossibility of forming tektites by impact "jetting" or "compression rebound".
In 1961, officials at the U.S. Air Force's Cambridge Research Laboratories in
Bedford, MassachusettsBedford is a town in Middlesex County, Massachusetts, United States. It is within the Greater Boston area, north-west of the city of Boston. The population of Bedford was 13,320 at the 2010 census.- History :...
, were keenly interested in the chemical and physical characteristics of tektites. "Project 7698" was commissioned with W.H. Pinson, Jr. of the Massachusetts Institute of Technology as the principal investigator. The 7698 final report concluded that the
strontiumStrontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
isotopic composition of tektites did not match those of terrestrial rocks and impactites. Pinson concluded the theory of formation by random fusion of terrestrial materials "whether by impact of meteorites, asteroids, comets or lightning" could not be supported.
NASA scientist
John A. O'KeefeJohn Aloysius O'Keefe was a planetary scientist with the National Aeronautics and Space Administration from 1958 to 1995. He is credited with the discovery of Earth's "pear shape" using U.S. Vanguard satellite data collected in the late 1950s...
published numerous papers between the 1950s and 1990s discussing these lunar rare-earth, isotopic and other chemistries, and how they relate to tektite glass.
Thus, some tektite researchers continue to strongly disagree with the popular terrestrial-impact theory; they suggest tektites are more likely volcanic ejecta from the Moon.
From the 1950s through the 1990s,
NASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
aerodynamicist Dean R. Chapman and others advanced the "lunar origin" theory of tektites. Chapman used complex orbital computer models and extensive
wind tunnelA wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
tests to support the theory that the so-called Australasian tektites originated from the Rosse ejecta ray of the large crater
TychoTycho may refer to:* Tycho Brahe , Danish nobleman and astronomer* Tycho van Meer , Dutch field hockey striker* Tommy Tycho , Hungarian-Australian pianist, conductor, composerIn astronomy:...
on the
MoonThe 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...
's nearside. Until the Rosse ray is sampled, a lunar origin for these tektites cannot be ruled out. During the 1980s and 1990s, researchers such as O’Keefe of
NASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
, astronomer and long-time tektite researcher Hal Povenmire, and petrologist Darryl Futrell claimed that the slow way in which tektite glass formed (called "fining"), and the volcanic features they claimed to have observed within some layered tektites, could not be explained by the terrestrial-impact theory. Unlike all terrestrial impactite glasses, tektites are nearly free of internal
waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, similar to lunar rocks. Also,
Stokes' LawIn 1851, George Gabriel Stokes derived an expression, now known as Stokes' law, for the frictional force – also called drag force – exerted on spherical objects with very small Reynolds numbers in a continuous viscous fluid...
does not permit the formation of tektites during impact while the velocity needed to form certain "flanged" tektites is more compatible with a lunar origin rather than a terrestrial origin. O'Keefe suggested explosive, hydrogen-driven lunar volcanoes as the original source of tektites. Note: Since the unmanned U.S. Clementine lunar mission of the 1990s, vast areas of pyroclastic (volcanic) glasses have been identified, notably in the area of the Aristarchus plateau. There is also evidence of interstitial granitic material (akin to the acidic tektites in chemistry) in some lunar highland samples which bolsters the lunar-origin theory. Lunar Orbiter spacecraft images reveal fields of volcanic domes that may indicate deep-seated, high-silica eruptions on the Moon, possible sources of the tektites. (These domes are similar to the Mono Lake craters of California; ironically, Mono obsidians resemble some layered tektites).
Occurrence
The
Moldau RiverThe Vltava is the longest river in the Czech Republic, running north from its source in Šumava through Český Krumlov, České Budějovice, and Prague, merging with the Elbe at Mělník...
(in Czech, Vltava) in the Czech Republic is now the only known locality for green, translucent tektite. The first tektites were found in 1787 in the Moldau River, hence their original name of "moldavites." Other color varieties of this natural glass have since been found in many different localities. Tektites are usually translucent and occur in a range of colors from green to brown. Their surfaces are usually uneven or rough, with a distinctive lumpy, jagged, or scarred texture. Tektites do not contain the crystallites found in obsidian. They may, however, have characteristic inclusions of round or torpedo-shaped bubbles or honeylike swirls.
Tektites from Thailand have been carved as small, decorative objects worn in the belief that they give protection from evil.
Books
- J. Baier: Zur Herkunft und Bedeutung der Ries-Auswurfprodukte für den Impakt-Mechanismus. - Jber. Mitt. oberrhein. geol. Ver., N. F. 91, 9-29, 2009.
- J. Baier: Die Auswurfprodukte des Ries-Impakts, Deutschland in Documenta Naturae, Vol. 162, München, 2007. ISBN 978-3-86544-162-1
- McCall, G.J.H. (2001) Tektites in the Geological Record, The Geological Society London, ISBN 1-86239-085-1
- O'Keefe, J.A., ed. (1963) Tektites, University of Chicago Press
- O'Keefe, J.A. (1976) Tektites and Their Origin, Elsevier, ISBN 0-444-41350-2
- Povenmire, Hal (1997) Tektites, a Cosmic Paradox
Articles
- Cameron, W. S. & Lowrey, B.E. (1975) Tektites: Volcanic ejecta from the Moon. The Moon, 31–360.
- Chapman, Dean R. (1971) Australasian tektite geographic pattern, crater and ray of origin, and theory of tektite events. Journal of Geophysical Research, Vol. 76, No. 26, 6309–6338.
- Chao, E.C.T. (1993) Comparison of the Cretaceous-Tertiary boundary impact events and the 0.77-ma Australasian tektite event... U.S.G.S. Survey Bulletin 2050, G.P.O.
- Faul H.(1966) Tektites are terrestrial. Science, Vol. 152, 1341–1345.
- Futrell, D. (February & March 1999) The lunar origin of tektites. Rock & Gem.
- Futrell, D. & Varricchio, L. (2002) An argument against the terrestrial origin of tektites. Meteorite, Vol. 8, No. 4, pp. 34–35.
- Glass, B. P. (1986) Lunar sample 14425: Not a lunar tektite, Geochimica et Cosmochimica Acta 50, 111–113.
- Koeberl C.(1990) The geochemistry of tektites: An overview. Tectonophysics Vol. 171, 405–422.
- Mason, B. & Melson, W.G. (1970) The lunar rocks. Wiley Interscience, 113–115.
- NASA Ames Research Center (Sept. 22, 1969) NASA fact sheet Tektites, tons of the Moon already on Earth.
- O'Keefe, J.A. (June 5, 1970) Tektite glass in Apollo 12 sample. Science, Vol 168, 1209–1210.
- O'Keefe, J.A. (Feb. 26, 1985) The coming revolution in planetology. Eos, Vol. 66, No. 9, pp. 89–90.
- O'Keefe, J.A. (1993)The origin of tektites.Meteoritics, Vol. 29, No. 1, pp. 73–78.
External links