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Eratosthenian
The Eratosthenian period in the lunar geologic timescale runs from 3,200 million years ago to 1,100 million years ago. It is named after the crater Eratosthenes, which displays characteristics typical of craters of this age, including a surface that is not significantly eroded by subsequent impacts, but which also does not possess a ray system. The massive basaltic volcanism of the Imbrian period tapered off and ceased during this long span of lunar time. The youngest lunar lava flows identified from orbital images are tentatively placed near the end of this period. Its equivalent on Earth consists of most of the Mesoarchean and Neoarchean eras (Archean eon), Paleoproterozoic and Mesoproterozoic eras ( Proterozoic eon). Examples Other than Eratosthenes itself, examples of large Eratosthenian craters on the near side of the Moon include Langrenus, Macrobius, Aristoteles, Hausen, Moretus, Pythagoras, Scoresby, Bullialdus, Plutarch Plutarch (; , ''Ploútarchos'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lunar Geologic Timescale
The lunar geological timescale (or selenological timescale) divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian ( Late and Early epochs), Nectarian, and Pre-Nectarian. The boundaries of this time scale are related to large impact events that have modified the lunar surface, changes in crater formation through time, and the size-frequency distribution of craters superposed on geological units. The absolute ages for these periods have been constrained by radiometric dating of samples obtained from the lunar surface. However, there is still much debate concerning the ages of certain key events, because correlating lunar regolith samples with geological units on the Moon is difficult, and most lunar radiometric ages have been highly affected by an intense history of bombardment. Lunar stratigraphy The primary geological processes that have modified the lunar surface are impact cratering and volcanism, and by using ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eratosthenes (crater)
Eratosthenes crater is a relatively deep lunar impact crater that lies on the boundary between the Mare Imbrium and Sinus Aestuum mare regions. It forms the western terminus of the Montes Apenninus mountain range. It is named after ancient Greek astronomer Eratosthenes of Cyrene, who estimated the circumference of the Earth, and the distance from the Earth to the Sun. Description The crater has a well-defined circular rim, terraced inner wall, central mountain peaks, an irregular floor, and an outer rampart of ejecta. It lacks a ray system of its own, but is overlain by rays from the prominent crater Copernicus to the south-west. The Eratosthenian period in the lunar geological timescale is named after this crater, though it does not define the start of this time period. The crater is believed to have been formed about 3.2 billion years ago. At low Sun-angles, this crater is prominent due to the shadow cast by the rim. When the Sun is directly overhead, however, Eratosth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Langrenus (crater)
Langrenus is an impact crater located near the eastern lunar limb. The feature is circular in shape, but appears oblong due to foreshortening. It lies on the eastern shore of the Mare Fecunditatis. To the south is the overlapping crater pair Vendelinus and the smaller Lamé. The inner wall of Langrenus is wide and irregularly terraced, with an average width of about 20 kilometers. The outer ramparts are irregular and hilly, and there is a bright, fragmented ray system spread across the mare to the west. The interior of the crater has a higher albedo than the surroundings, so the crater appears bright when the Sun is overhead. The crater floor is covered by many boulders, and is slightly irregular in the northwest half. The central peaks rise about a kilometer above the floor, and a peak on the eastern rim ascends to an altitude of 3 km. On December 30, 1992, Audouin Dollfus of the Observatoire de Paris observed a series of glows on the floor of this crater using the one ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bullialdus (crater)
Bullialdus is a lunar impact crater located in the western part of the Mare Nubium. It was named after French astronomer Ismaël Boulliau. To the north by north-west is the broken-rimmed and lava-flooded crater Lubiniezky. South-west of Bullialdus lies the smaller crater König. The relatively isolated location of this crater serves to highlight its well-formed shape. Bullialdus has a high outer rim that is circular but observers have noted a slightly polygonal appearance. The inner walls are terraced and contain many signs of landslips. The outer ramparts are covered in a wide ''ejecta'' blanket that highlights a radial pattern of low ridges and valleys. In the center of the crater is a formation of several peaks and rises that climb to over a kilometer in height. A raised ridge runs from the peaks to the south-east, until finally merging with the inner wall. The floor of the crater is generally rough with many low rises. Overall it has a somewhat convex shape, bulgin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pythagoras (crater)
Pythagoras is a prominent impact crater located near the northwestern limb of the Moon. It lies just to the northwest of the somewhat larger Babbage. The crater has an oval appearance due to the oblique viewing angle. Only the western face of the interior can be viewed from the Earth, the other side being permanently out of sight. The well-preserved rim of Pythagoras has a wide terrace system, and a slight rampart around the exterior. Although generally circular, the crater outline has a hexagonal form. The floor is flattened, but with an irregular, hilly surface. There is evidence of landslips around the periphery. In the center is a sharp, mountainous rise with a double peak that ascends 1.5 kilometers above the crater floor. Pythagoras is a crater of Eratosthenian age. |
Aristoteles (crater)
Aristoteles is a lunar impact crater that lies near the southern edge of the Mare Frigoris and to the east of the Montes Alpes mountain range. It was officially named in 1935 after the ancient Greek philosopher Aristotle by the International Astronomical Union, using the classical form of his name. To the immediate south of Aristoteles lies the slightly smaller crater Eudoxus, and these two form a distinctive pair for a telescope observer. An arc of mountains between these craters bends to the west before joining the walls. The smaller crater Mitchell is directly attached to the eastern rim of Aristoteles. To the west is the low, flooded feature Egede. Observers have noted the crater wall of Aristoteles is slightly distorted into a rounded hexagon shape. The inner walls are wide and finely terraced. The outer ramparts display a generally radial structure of hillocks through the extensive blanket of ''ejecta''. The crater floor is uneven and covered in hilly ripples. Aristotel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hausen (crater)
Hausen is a large Lunar craters, lunar impact crater that lies along the south-southwestern limb of the Moon. It was named after German astronomer Christian August Hausen, Christian A. Hausen by the International Astronomical Union, IAU in 1961. The visibility of this crater is significantly affected by libration effects, although even under the very best of conditions it is viewed nearly from on edge. It lies along the western edge of the immense walled plain Bailly (crater), Bailly. To the northeast is the crater Pingré (crater), Pingré on the near side, and to the north is the Arrhenius (lunar crater), Arrhenius just on the Far side (Moon), far side of the lunar limb. The rim of this crater is generally circular, with an outward bulge to the south-southeast. The inner wall is wiktionary:terrace, terraced at the northern and southern ends, and is more irregular along the eastern and western flanks. The rim along the east and southeast flanks displays slumping, producing a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleoproterozoic
The Paleoproterozoic Era (also spelled Palaeoproterozoic) is the first of the three sub-divisions ( eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from (2.5–1.6 Ga). It is further subdivided into four geologic periods, namely the Siderian, Rhyacian, Orosirian and Statherian. Paleontological evidence suggests that the Earth's rotational rate ~1.8 billion years ago equated to 20-hour days, implying a total of ~450 days per year. It was during this era that the continents first stabilized. Atmosphere The Earth's atmosphere was originally a weakly reducing atmosphere consisting largely of nitrogen, methane, ammonia, carbon dioxide and inert gases, in total comparable to Titan's atmosphere. When oxygenic photosynthesis evolved in cyanobacteria during the Mesoarchean, the increasing amount of byproduct dioxygen began to deplete the reductants in the ocean, land surface and the atmosphere. Eventually all surf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ray System
In planetary geology, a ray system comprises radial streaks of fine '' ejecta'' thrown out during the formation of an impact crater, looking somewhat like many thin spokes coming from the hub of a wheel. The rays may extend for lengths up to several times the diameter of their originating crater, and are often accompanied by small secondary craters formed by larger chunks of ejecta. Ray systems have been identified on the Moon, Earth ( Kamil Crater), Mercury, and some moons of the outer planets. Originally it was thought that they existed only on planets or moons lacking an atmosphere, but more recently they have been identified on Mars in infrared images taken from orbit by '' 2001 Mars Odyssey''s thermal imager. Rays appear at visible, and in some cases infrared wavelengths, when ejecta are made of material with different reflectivity (i.e., albedo) or thermal properties from the surface on which they are deposited. Typically, visible rays have a higher albedo than th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kirkwood (crater)
Kirkwood is a well-formed lunar impact crater that is located on the far side of the Moon, on the northern hemisphere, approximately 68 kilometers in diameter. It lies just to the northeast of the crater Sommerfeld, and Hippocrates is located to the east-northeast. It was named after American astronomer Daniel Kirkwood. Description The perimeter of this crater is generally circular, with a few slight outward notches particularly to the southeast. It displays very little appearance of wear, and neither the interior nor the outer rampart Rampart may refer to: * Rampart (fortification), a defensive wall or bank around a castle, fort or settlement Rampart may also refer to: * LAPD Rampart Division, a division of the Los Angeles Police Department ** Rampart scandal, a blanket ter ... are marked by any craters of note. The inner wall has slumped somewhat, and has formed a few terrace-like structures. The interior ejecta spreads a good way across the inner floor, coverin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Finsen (crater)
Finsen is a lunar impact crater that is located in the southern hemisphere, on the Moon's far side. It is attached to the southeastern exterior of the walled plain Leibnitz, and the ejecta from Finsen covers the southeastern part of Leibnitz's interior floor. To the southwest of Finsen is another walled plain, Von Kármán, partly overlain by Leibnitz. This is a relatively young impact crater with well-defined features that have not been significantly eroded by subsequent impacts. The rim is circular but somewhat uneven along the edge, with outward protrusions along all sides except to the north and northwest. The inner wall has slumped in places, producing a sharp rim edge in the southern half. There are also a number of short terraces along the inner wall. The inner wall is wider to the north, and so the relatively level interior floor is offset slightly to the south. At the midpoint of the crater is a central peak formation, occupying an area of roughly 15 km. This ce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Birkeland (lunar Crater)
Birkeland is a lunar impact crater that lies in the southern hemisphere on the far side of the Moon. This crater is attached to the central waist of the oddly shaped Van de Graaff crater formation, and may partly account for that crater's figure-8 shape. To the southeast is the large walled plain Leibnitz. This crater has not been significantly eroded, and the outer rim is well-defined with a well-terrace Terrace may refer to: Landforms and construction * Fluvial terrace, a natural, flat surface that borders and lies above the floodplain of a stream or river * Terrace, a street suffix * Terrace, the portion of a lot between the public sidewalk a ...d inner walls around much of the interior. The rim has a slight inward bulge along the north where it is attached to the Van de Graaff formation. The interior floor is relatively level, except in the southeast where there is some rough terrain. There is a central peak formation at the midpoint. Satellite craters By convention th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
