DOCSLIB.ORG

Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System Landscapes with Craters 1 Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System 1.1. THE NEW GEOLOGY: METEORITE planets, including Earth (Taylor, 1982, Chapter 3; 1992, IMPACTS ON THE EARTH Chapter 4); and (2) the ability to definitely identify terres- trial impact structures, especially large or ancient ones, During the last 30 years, there has been an immense and by the presence of unique petrological and geochemical unexpected revolution in our picture of Earth and its place criteria, particularly the distinctive shock-metamorphic in the solar system. What was once a minor astronomical effects produced in rocks and minerals by the intense shock process has become an important part of the geological main- waves generated in impact events (French, 1968a; French and stream. Impacts of extraterrestrial objects on the Earth, once Short, 1968). regarded as an exotic but geologically insignificant process, In the last few decades, geologists have gradually realized have now been recognized as a major factor in the geological that collisions of extraterrestrial objects with Earth — and and biological history of the Earth. Scientists and the public especially the rare but catastrophic impacts of kilometer-sized have both come to realize that terrestrial impact structures asteroids and comets — have significantly shaped Earth’s are more abundant, larger, older, more geologically complex, surface, disturbed its crust, and altered its geological history more economically important, and even more biologically (French, 1968a, 1990b; Shoemaker, 1977; Grieve, 1987, 1990, significant than anyone would have predicted a few decades 1991; Nicolaysen and Reimold, 1990; Pesonen and Henkel, ago. Impact events have generated large crustal disturbances, 1992; Dressler et al., 1994). produced huge volumes of igneous rocks, formed major The record of impacts on Earth is still being deciphered. ore deposits, and participated in at least one major biologi- Approximately 150 individual geological structures have cal extinction. already been identified as the preserved results of such im- Before the 1960s, collisions of extraterrestrial objects with pacts (Grieve, 1991, 1994; Grieve et al., 1995; Grieve and the Earth were not considered significant. Geologists did Pesonen, 1992, 1996), and it is estimated that several hun- agree (and had agreed since the early 1800s) that pieces of dred more impact structures remain to be identified (Trefil extraterrestrial material did occasionally penetrate the atmos- and Raup, 1990; Grieve, 1991). The known impact struc- phere and strike Earth’s surface, but the only visible results tures (Fig. 1.2) range from small circular bowls only a few of such collisions were a collection of meteorites to study kilometers or less in diameter (Fig. 1.1) to large complex and display in museums, together with a few small and structures more than 200 km in diameter and as old as geologically short-lived meteorite craters, usually located in 2 Ga (Figs. 1.3 and 1.4). Formation of the larger features, out-of-the-way desert areas (Fig. 1.1). Almost no one be- such as the Sudbury (Canada) and Vredefort (South Africa) lieved that extraterrestrial objects could produce major geo- structures, involved widespread disturbances in Earth’s crust logical effects or that such projectiles could be any more than and major perturbations in the geologic history of the re- a local hazard. gions where they were formed. This simple view has changed drastically, and the change In addition to the geological disturbances involved, im- reflects two major factors: (1) explorations of the solar sys- pact events have produced several geological structures tem by humans and robotic spacecraft, which have estab- with actual economic value; a production value of about lished the importance of impact cratering in shaping all the $5 billion per year has been estimated for North American 1 2 Traces of Catastrophe Fig. 1.1. A simple impact crater. Barringer Meteor Crater (Arizona), a young, well-preserved, and well-known impact crater, 1.2 km in diameter, has become the type example for small, bowl-shaped impact craters of the simple type. The crater was formed about 50,000 years ago when an iron meteorite approximately 30 m across struck the horizontal sediments of northern Arizona’s Colorado Plateau. After decades of controversy, the impact origin of the crater has been firmly established by the presence of preserved iron meteorites, the recognition of unique shock-metamorphic features in its rocks, and geological studies that detailed the mechanisms of its formation. This aerial view, looking northwest, shows typical features of young simple impact craters: a well-preserved near-circular outline, an uplifted rim, and hummocky deposits of ejecta just beyond the rim (e.g., white areas at lower left). The uplifted layers of originally horizontal sedimentary target rocks can be seen in the far rim of the crater at the right. (Photograph copyright D. J. Roddy; used with permission.) impact structures alone (Grieve and Masaitis, 1994). The eco- Terrestrial life itself has not escaped this cosmic bom- nomic products of impact structures include such diverse bardment. During the last 20 years an impressive amount of items as local building stone, diamonds, and uranium. evidence has accumulated to show that at least one large Hydrocarbons (petroleum and gas) are an especially impor- impact event about 65 m.y. ago redirected biological evolu- tant product from impact structures (Donofrio, 1997; Johnson tion on Earth by producing the major extinction that now and Campbell, 1997). Large impacts crush and shatter the marks the boundary between the Cretaceous and Tertiary target rocks extensively beneath and around the crater; in a periods, the point at which the dinosaurs died and mam- few structures [e.g., Ames (Oklahoma); Red Wing Creek mals (our ancestors) became major players in the history of (North Dakota)], the resulting breccia zones have served as terrestrial life (Alvarez et al., 1980; Silver and Schultz, 1982; traps for oil and gas. Within and around other impact cra- McLaren and Goodfellow, 1990; Sharpton and Ward, 1990; ters, the other kinds of breccias produced by the impact Ryder et al., 1996; Alvarez, 1997). The giant crater produced have provided building stone [Ries Crater (Germany); by that collision has now been definitely identified, a struc- Rochechouart (France)] and industrial limestone [Kentland ture [Chicxulub (Mexico)] at least 180 km across, completely (Indiana)]. In some cases, the sediments that subsequently buried under the younger sediments of Mexico’s Yucatán fill the crater depressions may contain deposits of such eco- Peninsula (Hildebrand et al., 1991; Sharpton et al., 1992; nomic materials as oil shale [Boltysh (Ukraine)], diatomite Morgan et al., 1997). Active debates continue about how this [Ragozinka (Russia)], gypsum [Lake St. Martin (Canada)], catastrophic event actually produced the extinction and and lead-zinc ores [Crooked Creek (Missouri)]. whether similar impacts have caused the other major and The biggest impact-related bonanza (current production minor extinctions recorded in the geologic record. about $2 billion per year) is the Sudbury structure (Canada), Although the recognition of impact events and their ef- which contains one of the largest nickel-copper sulfide de- fects on Earth has been marked by debate and controversy posits on Earth (Guy-Bray, 1972; E. G. Pye et al., 1984; (e.g., Dietz, 1963; Bucher, 1963; French, 1968a, 1990b; Dressler et al., 1994; Lightfoot and Naldrett, 1994). The de- Sharpton and Grieve, 1990; Nicolaysen and Reimold, 1990), posit occurs at the base of a large igneous body (the Sudbury there is no longer any need to demonstrate either the exist- Igneous Complex), which is in turn emplaced in a large, com- ence or the importance of such impact events. The young plex, and highly deformed impact basin nearly 2 b.y. old. but maturing science of impact geology is turning toward Fig. 1.2. Distribution of terrestrial impact structures. Locations of 145 currently known terrestrial im- pact structures (see Grieve, 1991; Grieve et al., 1995; Grieve and Pesonen, 1996; Koeberl and Anderson, 1996b). The clearly nonrandom geographic distribution reflects geological and social factors rather than the original random bombardment flux: (1) increased preservation of impact structures on continental shield and cratonic areas that have been stable, and not deeply eroded, over long periods of time; (2) the restriction of past studies to continental areas, and a lack of systematic searches for submarine impact Landscapes withCraters structures; (3) the active research and discoveries of particular workers, especially in Canada (Beals et al., 1963; Dence, 1965; Dence et al., 1968), Russia (Masaitis et al., 1980) and Ukraine (Gurov and Gurova, 1991), Fennoscandia (Pesonen, 1996; Pesonen and Henkel, 1992), and Australia (Glikson, 1996b; Shoemaker and Shoemaker, 1996). The observed distributions of crater sizes and ages (inset) have been biased by postimpact geological processes; the ages of the great majority of preserved impact structures are <200 Ma, and small structures (0–5 km diameter) are greatly underrepresented. Diagram courtesy of V. L. Sharpton. 3 4 Traces of Catastrophe or volcanic activity) had been debated for just as long (for historical reviews, see Hoyt, 1987; Mark, 1987; Wilhelms, 1993). The Apollo program provided better views of the lu- nar surface, as well as samples returned
Load more

Recommended publications
  • 3-D Seismic Characterization of a Cryptoexplosion Structure
    Cryptoexplosion structure 3-D seismic characterization of a eryptoexplosion structure J. Helen Isaac and Robert R. Stewart ABSTRACT Three-quarters of a circular structure is observed on three-dimensional (3-D) seismic data from James River, Alberta. The structure has an outer diameter of 4.8 km and a raised central uplift surrounded by a rim synform. The central uplift has a diameter of 2.4 km and its crest appears to be uplifted about 400 m above regional levels. The structure is at a depth of about 4500 m. This is below the zone of economic interest and the feature has not been penetrated by any wells. The disturbed sediments are interpreted to be Cambrian. We infer that the structure was formed in Late Cambrian to Middle Devonian time and suffered erosion before the deposition of the overlying Middle Devonian carbonates. Rim faults, probably caused by slumping of material into the depression, are observed on the outside limb of the synform. Reverse faults are evident underneath the feature and the central uplift appears to have coherent internal reflections. The amount of uplift decreases with increasing depth in the section. The entire feature is interpreted to be a cryptoexplosion structure, possibly caused by a meteorite impact. INTRODUCTION Several enigmatic circular structures, of different sizes and ages, have been observed on seismic data from the Western Canadian sedimentary basin (WCSB) (e.g., Sawatzky, 1976; Isaac and Stewart, 1993) and other parts of Canada (Scott and Hajnal, 1988; Jansa et al., 1989). The structures present startling interruptions in otherwise planar seismic features.
    [Show full text]
  • Lunar Impact Crater Identification and Age Estimation with Chang’E
    ARTICLE https://doi.org/10.1038/s41467-020-20215-y OPEN Lunar impact crater identification and age estimation with Chang’E data by deep and transfer learning ✉ Chen Yang 1,2 , Haishi Zhao 3, Lorenzo Bruzzone4, Jon Atli Benediktsson 5, Yanchun Liang3, Bin Liu 2, ✉ ✉ Xingguo Zeng 2, Renchu Guan 3 , Chunlai Li 2 & Ziyuan Ouyang1,2 1234567890():,; Impact craters, which can be considered the lunar equivalent of fossils, are the most dominant lunar surface features and record the history of the Solar System. We address the problem of automatic crater detection and age estimation. From initially small numbers of recognized craters and dated craters, i.e., 7895 and 1411, respectively, we progressively identify new craters and estimate their ages with Chang’E data and stratigraphic information by transfer learning using deep neural networks. This results in the identification of 109,956 new craters, which is more than a dozen times greater than the initial number of recognized craters. The formation systems of 18,996 newly detected craters larger than 8 km are esti- mated. Here, a new lunar crater database for the mid- and low-latitude regions of the Moon is derived and distributed to the planetary community together with the related data analysis. 1 College of Earth Sciences, Jilin University, 130061 Changchun, China. 2 Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, 100101 Beijing, China. 3 Key Laboratory of Symbol Computation and Knowledge Engineering of Ministry of Education, College of Computer Science and Technology, Jilin University, 130012 Changchun, China. 4 Department of Information Engineering and Computer ✉ Science, University of Trento, I-38122 Trento, Italy.
    [Show full text]
  • Fire History and Climate Change
    Synthesis of Knowledge: Fire History and Climate Change William T. Sommers Stanley G. Coloff Susan G. Conard JFSP Project 09‐2‐01‐09 Sommers, William T., Stanley G. Coloff and Susan G. Conard 2011: Fire History and Climate Change. Report Submitted to the Joint Fire Science Program for Project 09‐2‐01‐09. 215 pages + 6 Appendices Abstract This report synthesizes available fire history and climate change scientific knowledge to aid managers with fire decisions in the face of ongoing 21st Century climate change. Fire history and climate change (FHCC) have been ongoing for over 400 million years of Earth history, but increasing human influences during the Holocene epoch have changed both climate and fire regimes. We describe basic concepts of climate science and explain the causes of accelerating 21st Century climate change. Fire regimes and ecosystem classifications serve to unify ecological and climate factors influencing fire, and are useful for applying fire history and climate change information to specific ecosystems. Variable and changing patterns of climate‐fire interaction occur over different time and space scales that shape use of FHCC knowledge. Ecosystem differences in fire regimes, climate change and available fire history mean using an ecosystem specific view will be beneficial when applying FHCC knowledge. Authors William T. Sommers is a Research Professor at George Ma‐ son University in Fairfax, Virginia. He completed a B.S. de‐ gree in Meteorology from the City College of New York, a Acknowledgements S.M. degree in Meteorology from the Massachusetts Insti‐ We thank the Joint Fire Sciences Program for tute of Technology and a Ph.D.
    [Show full text]
  • Cross-References ASTEROID IMPACT Definition and Introduction History of Impact Cratering Studies
    18 ASTEROID IMPACT Tedesco, E. F., Noah, P. V., Noah, M., and Price, S. D., 2002. The identification and confirmation of impact structures on supplemental IRAS minor planet survey. The Astronomical Earth were developed: (a) crater morphology, (b) geo- 123 – Journal, , 1056 1085. physical anomalies, (c) evidence for shock metamor- Tholen, D. J., and Barucci, M. A., 1989. Asteroid taxonomy. In Binzel, R. P., Gehrels, T., and Matthews, M. S. (eds.), phism, and (d) the presence of meteorites or geochemical Asteroids II. Tucson: University of Arizona Press, pp. 298–315. evidence for traces of the meteoritic projectile – of which Yeomans, D., and Baalke, R., 2009. Near Earth Object Program. only (c) and (d) can provide confirming evidence. Remote Available from World Wide Web: http://neo.jpl.nasa.gov/ sensing, including morphological observations, as well programs. as geophysical studies, cannot provide confirming evi- dence – which requires the study of actual rock samples. Cross-references Impacts influenced the geological and biological evolu- tion of our own planet; the best known example is the link Albedo between the 200-km-diameter Chicxulub impact structure Asteroid Impact Asteroid Impact Mitigation in Mexico and the Cretaceous-Tertiary boundary. Under- Asteroid Impact Prediction standing impact structures, their formation processes, Torino Scale and their consequences should be of interest not only to Earth and planetary scientists, but also to society in general. ASTEROID IMPACT History of impact cratering studies In the geological sciences, it has only recently been recog- Christian Koeberl nized how important the process of impact cratering is on Natural History Museum, Vienna, Austria a planetary scale.
    [Show full text]
  • Daguerreian Annual 1990-2015: a Complete Index of Subjects
    Daguerreian Annual 1990–2015: A Complete Index of Subjects & Daguerreotypes Illustrated Subject / Year:Page Version 75 Mark S. Johnson Editor of The Daguerreian Annual, 1997–2015 © 2018 Mark S. Johnson Mark Johnson’s contact: [email protected] This index is a work in progress, and I’m certain there are errors. Updated versions will be released so user feedback is encouraged. If you would like to suggest possible additions or corrections, send the text in the body of an email, formatted as “Subject / year:page” To Use A) Using Adobe Reader, this PDF can be quickly scrolled alphabetically by sliding the small box in the window’s vertical scroll bar. - or - B) PDF’s can also be word-searched, as shown in Figure 1. Many index citations contain keywords so trying a word search will often find other instances. Then, clicking these icons Figure 1 Type the word(s) to will take you to another in- be searched in this Adobe Reader Window stance of that word, either box. before or after. If you do not own the Daguerreian Annual this index refers you to, we may be able to help. Contact us at: [email protected] A Acuna, Patricia 2013: 281 1996: 183 Adams, Soloman; microscopic a’Beckett, Mr. Justice (judge) Adam, Hans Christian d’types 1995: 176 1995: 194 2002/2003: 287 [J. A. Whipple] Abbot, Charles G.; Sec. of Smithso- Adams & Co. Express Banking; 2015: 259 [ltr. in Boston Daily nian Institution deposit slip w/ d’type engraving Evening Transcript, 1/7/1847] 2015: 149–151 [letters re Fitz] 2014: 50–51 Adams, Zabdiel Boylston Abbott, J.
    [Show full text]
  • Detecting and Avoiding Killer Asteroids
    Target Earth! Detecting and Avoiding Killer Asteroids by Trudy E. Bell (Copyright 2013 Trudy E. Bell) ARTH HAD NO warning. When a mountain- above 2000°C and triggering earthquakes and volcanoes sized asteroid struck at tens of kilometers (miles) around the globe. per second, supersonic shock waves radiated Ocean water suctioned from the shoreline and geysered outward through the planet, shock-heating rocks kilometers up into the air; relentless tsunamis surged e inland. At ground zero, nearly half the asteroid’s kinetic energy instantly turned to heat, vaporizing the projectile and forming a mammoth impact crater within minutes. It also vaporized vast volumes of Earth’s sedimentary rocks, releasing huge amounts of carbon dioxide and sulfur di- oxide into the atmosphere, along with heavy dust from both celestial and terrestrial rock. High-altitude At least 300,000 asteroids larger than 30 meters revolve around the sun in orbits that cross Earth’s. Most are not yet discovered. One may have Earth’s name written on it. What are engineers doing to guard our planet from destruction? winds swiftly spread dust and gases worldwide, blackening skies from equator to poles. For months, profound darkness blanketed the planet and global temperatures dropped, followed by intense warming and torrents of acid rain. From single-celled ocean plank- ton to the land’s grandest trees, pho- tosynthesizing plants died. Herbivores starved to death, as did the carnivores that fed upon them. Within about three years—the time it took for the mingled rock dust from asteroid and Earth to fall out of the atmosphere onto the ground—70 percent of species and entire genera on Earth perished forever in a worldwide mass extinction.
    [Show full text]
  • Extraordinary Rocks from the Peak Ring of the Chicxulub Impact Crater: P-Wave Velocity, Density, and Porosity Measurements from IODP/ICDP Expedition 364 ∗ G.L
    Earth and Planetary Science Letters 495 (2018) 1–11 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Extraordinary rocks from the peak ring of the Chicxulub impact crater: P-wave velocity, density, and porosity measurements from IODP/ICDP Expedition 364 ∗ G.L. Christeson a, , S.P.S. Gulick a,b, J.V. Morgan c, C. Gebhardt d, D.A. Kring e, E. Le Ber f, J. Lofi g, C. Nixon h, M. Poelchau i, A.S.P. Rae c, M. Rebolledo-Vieyra j, U. Riller k, D.R. Schmitt h,1, A. Wittmann l, T.J. Bralower m, E. Chenot n, P. Claeys o, C.S. Cockell p, M.J.L. Coolen q, L. Ferrière r, S. Green s, K. Goto t, H. Jones m, C.M. Lowery a, C. Mellett u, R. Ocampo-Torres v, L. Perez-Cruz w, A.E. Pickersgill x,y, C. Rasmussen z,2, H. Sato aa,3, J. Smit ab, S.M. Tikoo ac, N. Tomioka ad, J. Urrutia-Fucugauchi w, M.T. Whalen ae, L. Xiao af, K.E. Yamaguchi ag,ah a University of Texas Institute for Geophysics, Jackson School of Geosciences, Austin, USA b Department of Geological Sciences, Jackson School of Geosciences, Austin, USA c Department of Earth Science and Engineering, Imperial College, London, UK d Alfred Wegener Institute Helmholtz Centre of Polar and Marine Research, Bremerhaven, Germany e Lunar and Planetary Institute, Houston, USA f Department of Geology, University of Leicester, UK g Géosciences Montpellier, Université de Montpellier, France h Department of Physics, University of Alberta, Canada i Department of Geology, University of Freiburg, Germany j SM 312, Mza 7, Chipre 5, Resid.
    [Show full text]
  • Destination Moon
    Ill ".=\'.\, . : t.\ i...ii. 4'i.' --- v 1, 2*..- e> . 1.... ...*f. - .. .. .../C-'.»i.:5.1:• \ I: .. ...: ... ':4r-... - i.. ·.· I . I ·#. - I, :P.k 0 1 '. -1-3:Z:,ile<52.4 -2. .3••••4 - ....., 1 - I ..... 3/4 I <:.9, . /•/f••94*/ ,,iS· .... I ... ....... 9492./i- ..·,61« 4/.th_ r-*- .. -I,r * 116.-452*:••:il-.--•• . .....a• 1 --, •.11:E I . ".59/.-R:&6.Aidillizatu:ill'Illrclilllll 9 St" "' 4.... ... 'Ablf*liE•*.0/8/49/18•09#J'£• .-t-i «, ...' '-t ---- ·· -.t-:.:.'• --,•1*4*14-=..»r,3.hk= 4-lk/ *7·· •-,·:s - '' 21:1 . -0.6..ts-9....4559*"4914*Em'6rt'" .. « 036 ·.. '.... ..'·2&4:i•#+,M/ri:.1*-%,TYRf/036B.e... - ....2:'. .. *... '. '!..i. '':3..i-,f....35"ti F:Y.'..t•: &.....:. 39•'.•........ - ..., ..7. .- P 036.1..' -.Zi - , 93327 . « tr. 1 '. .- I . '.. I ... .'... 'SS> <13· '9•25 ."'t-·,·:·- " :· •t :Ali.•'.'; • - 'r ...• r..... ' ... .... .. " .4 4 ..2- -.*.. 3. .. : , _sry»5433.5.,+· i<29*643, W5• ./'..'r· -. 4-··./.-i--fR...1-L...'.te....bkir.i<Ativi•haRN,1.254i'*"*61»4-=•• 6.... 61 . 31 /'- 5 301... ....•L . , . - - . '2.1 . ' -' »4 /2/323#9/44 ZEIII:ill)*lill//Il/6,1-'.cri:rre I. p ·: , 4 ·,.3*4,·to.4.-•44 4 .,I-tS••7•,<•.•·:L,4..'::....,i... ..I·."i271/Ve;*m#6:d 54.... .. -,•....- . I..,418'I.,4I.,•....6..#i r:'.,:•St»1.·:·'7· ···- . t'-.,jit- 1-6#.19.-'*-. ' -e - .c, .•.. C'!•-042,.-• .... -I ./- =r- . 2 2. -" ' .t. · '., -042,,. ' '/.9. •SS ..2.. 11•11•»..••...qwGILLET+*frs'.. :. " . .... I .- , .. - ....,.k.... -< 3.5*«· ·: . ' i.1., li-, f 20- PR :21 . 0• . c. .Fh: ---, 1.4':. '•,. -,-t.Z:ft,•• •'r,4.4, 4 r • .
    [Show full text]
  • Widespread Crater-Related Pitted Materials on Mars: Further Evidence for the Role of Target Volatiles During the Impact Process ⇑ Livio L
    Icarus 220 (2012) 348–368 Contents lists available at SciVerse ScienceDirect Icarus journal homepage: www.elsevier.com/locate/icarus Widespread crater-related pitted materials on Mars: Further evidence for the role of target volatiles during the impact process ⇑ Livio L. Tornabene a, , Gordon R. Osinski a, Alfred S. McEwen b, Joseph M. Boyce c, Veronica J. Bray b, Christy M. Caudill b, John A. Grant d, Christopher W. Hamilton e, Sarah Mattson b, Peter J. Mouginis-Mark c a University of Western Ontario, Centre for Planetary Science and Exploration, Earth Sciences, London, ON, Canada N6A 5B7 b University of Arizona, Lunar and Planetary Lab, Tucson, AZ 85721-0092, USA c University of Hawai’i, Hawai’i Institute of Geophysics and Planetology, Ma¯noa, HI 96822, USA d Smithsonian Institution, Center for Earth and Planetary Studies, Washington, DC 20013-7012, USA e NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA article info abstract Article history: Recently acquired high-resolution images of martian impact craters provide further evidence for the Received 28 August 2011 interaction between subsurface volatiles and the impact cratering process. A densely pitted crater-related Revised 29 April 2012 unit has been identified in images of 204 craters from the Mars Reconnaissance Orbiter. This sample of Accepted 9 May 2012 craters are nearly equally distributed between the two hemispheres, spanning from 53°Sto62°N latitude. Available online 24 May 2012 They range in diameter from 1 to 150 km, and are found at elevations between À5.5 to +5.2 km relative to the martian datum. The pits are polygonal to quasi-circular depressions that often occur in dense clus- Keywords: ters and range in size from 10 m to as large as 3 km.
    [Show full text]
  • Impact Cratering
    6 Impact cratering The dominant surface features of the Moon are approximately circular depressions, which may be designated by the general term craters … Solution of the origin of the lunar craters is fundamental to the unravel- ing of the history of the Moon and may shed much light on the history of the terrestrial planets as well. E. M. Shoemaker (1962) Impact craters are the dominant landform on the surface of the Moon, Mercury, and many satellites of the giant planets in the outer Solar System. The southern hemisphere of Mars is heavily affected by impact cratering. From a planetary perspective, the rarity or absence of impact craters on a planet’s surface is the exceptional state, one that needs further explanation, such as on the Earth, Io, or Europa. The process of impact cratering has touched every aspect of planetary evolution, from planetary accretion out of dust or planetesimals, to the course of biological evolution. The importance of impact cratering has been recognized only recently. E. M. Shoemaker (1928–1997), a geologist, was one of the irst to recognize the importance of this process and a major contributor to its elucidation. A few older geologists still resist the notion that important changes in the Earth’s structure and history are the consequences of extraterres- trial impact events. The decades of lunar and planetary exploration since 1970 have, how- ever, brought a new perspective into view, one in which it is clear that high-velocity impacts have, at one time or another, affected nearly every atom that is part of our planetary system.
    [Show full text]
  • A PROTEROZOIC 40Ar/39Ar AGE for the SUVASVESI SOUTH STRUCTURE (FINLAND)
    72nd Annual Meteoritical Society Meeting (2009) 5076.pdf A PROTEROZOIC 40Ar/39Ar AGE FOR THE SUVASVESI SOUTH STRUCTURE (FINLAND). E. Buchner1, M. Schmieder1, W. H. Schwarz2, M. Trieloff2, J. Moilanen3, T. Öhman4 and H. Stehlik5. 1Institut für Planetologie, Universität Stuttgart, D-70174 Stuttgart, Germany. Email: [email protected]. 2Institut für Geowissenschaften, Universität Heidelberg, D-69120 Heidelberg. 3Pinkelikatu 6 B 48, FI-90520 Oulu, Finland. 4Department of Geosciences, FI-90014 University of Oulu, Finland. 5Hagedornweg 2/2/12, A-1220 Vienna, Austria Introduction: The Suvasvesi North (diameter ~3.5 km) and South (diameter ~4.0 km) structures [1-3] in Finland are thought to represent a double impact crater system, similar to the Clearwater lakes in Canada [4]. As no isotopic data have so far been available, only the age of the ~1.88 Ga Paleoproterozoic (and some ~2.7 Ga Archean) crystalline target rocks of the Baltic Shield [1] is cited as the maximum impact age. Paleomagnetic data suggested either a Permo-Triassic (~230-280 Ma) or a Neoproterozoic (770-790 Ma) age for the Suvasvesi North impact structure [4,5]. We here present the first 40Ar/39Ar age for the Suvasvesi South structure. Samples and analytical procedure: Clast-poor particles of impact melt rock (87.1 mg) recovered by one of the authors (J. M.) from the Mannamäki area were chosen for 40Ar/39Ar dat- ing at the University of Heidelberg [6,7]. Results and interpretation: 40Ar/39Ar step-heating analysis yielded no plateau within a perturbed, hump-shaped [8] age spectrum with younger apparent ages (~100-450 Ma) within the low-temperature (T) heating steps (~13% of 39Ar released), older apparent ages (~820 Ma) in the mid-T fractions (~47% of 39Ar), and intermediate apparent ages (~715-710) Ma in the four final high-T steps (~40% of 39Ar).
    [Show full text]
  • George P. Merrill Collection, Circa 1800-1930 and Undated
    George P. Merrill Collection, circa 1800-1930 and undated Finding aid prepared by Smithsonian Institution Archives Smithsonian Institution Archives Washington, D.C. Contact us at [email protected] Table of Contents Collection Overview ........................................................................................................ 1 Administrative Information .............................................................................................. 1 Historical Note.................................................................................................................. 1 Descriptive Entry.............................................................................................................. 2 Names and Subjects ...................................................................................................... 3 Container Listing ............................................................................................................. 4 Series 1: PHOTOGRAPHS, CORRESPONDENCE AND RELATED MATERIAL CONCERNING INDIVIDUAL GEOLOGISTS AND SCIENTISTS, CIRCA 1800-1920................................................................................................................. 4 Series 2: PHOTOGRAPHS OF GROUPS OF GEOLOGISTS, SCIENTISTS AND SMITHSONIAN STAFF, CIRCA 1860-1930........................................................... 30 Series 3: PHOTOGRAPHS OF THE UNITED STATES GEOLOGICAL AND GEOGRAPHICAL SURVEY OF THE TERRITORIES (HAYDEN SURVEYS), CIRCA 1871-1877..............................................................................................................
    [Show full text]