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91-676: The moon was discovered by Italian astronomer Giovanni Domenico Cassini in 1684 and is named after the Titaness Dione in Greek mythology . Dione was first imaged up-close by the Voyager 1 space probe in 1980. Later, the Cassini spacecraft made multiple flybys of Dione throughout the 2000s and 2010s as part of its campaign to explore the Saturn system. Giovanni Domenico Cassini named

182-535: A characteristic fabric . All three types may melt again, and when this happens, new magma is formed, from which an igneous rock may once again solidify. Organic matter, such as coal, bitumen, oil, and natural gas, is linked mainly to organic-rich sedimentary rocks. To study all three types of rock, geologists evaluate the minerals of which they are composed and their other physical properties, such as texture and fabric . Geologists also study unlithified materials (referred to as superficial deposits ) that lie above

273-485: A petrographic microscope , where the minerals can be identified through their different properties in plane-polarized and cross-polarized light, including their birefringence , pleochroism , twinning , and interference properties with a conoscopic lens . In the electron microprobe, individual locations are analyzed for their exact chemical compositions and variation in composition within individual crystals. Stable and radioactive isotope studies provide insight into

364-434: A definite homogeneous chemical composition and an ordered atomic arrangement. Each mineral has distinct physical properties, and there are many tests to determine each of them. Minerals are often identified through these tests. The specimens can be tested for: A rock is any naturally occurring solid mass or aggregate of minerals or mineraloids . Most research in geology is associated with the study of rocks, as they provide

455-627: A length of less than a meter. Rocks at the depth to be ductilely stretched are often also metamorphosed. These stretched rocks can also pinch into lenses, known as boudins , after the French word for "sausage" because of their visual similarity. Where rock units slide past one another, strike-slip faults develop in shallow regions, and become shear zones at deeper depths where the rocks deform ductilely. The addition of new rock units, both depositionally and intrusively, often occurs during deformation. Faulting and other deformational processes result in

546-452: A means to provide information about geological history and the timing of geological events. The principle of uniformitarianism states that the geological processes observed in operation that modify the Earth's crust at present have worked in much the same way over geological time. A fundamental principle of geology advanced by the 18th-century Scottish physician and geologist James Hutton

637-406: A model of the planetary system that was in accord with the hypothesis of Nicolaus Copernicus. In 1661 he developed a method, inspired by Kepler's work, of mapping successive phases of solar eclipses; and in 1662 he published new tables of the sun, based on his observations at San Petronio." Cassini also rejected Newton's theory of gravity , after measurements he conducted which wrongly suggested that

728-608: A number of fields, laboratory, and numerical modeling methods to decipher Earth history and to understand the processes that occur on and inside the Earth. In typical geological investigations, geologists use primary information related to petrology (the study of rocks), stratigraphy (the study of sedimentary layers), and structural geology (the study of positions of rock units and their deformation). In many cases, geologists also study modern soils, rivers , landscapes , and glaciers ; investigate past and current life and biogeochemical pathways, and use geophysical methods to investigate

819-480: A position at the observatory at Panzano  [ it ] , near Bologna , to work with Marquis Cornelio Malvasia , a rich amateur astronomer, initiating the first part of his career. During his time at the Panzano Observatory , Cassini was able to complete his education under the scientists Giovanni Battista Riccioli and Francesco Maria Grimaldi . In 1650 the senate of Bologna appointed him as

910-580: A prominent mountain ridge on the leading hemisphere is best explained if there was a global subsurface liquid ocean like that of Enceladus. The ridge Janiculum Dorsa has a height of 1 to 2 km (0.6 to 1.2 miles); Dione's crust seems to pucker 0.5 km (0.3 miles) under it, suggesting that the icy crust was warm when the ridge formed, probably due to the presence of a subsurface liquid ocean, which increases tidal flexing. Giovanni Domenico Cassini Giovanni Domenico Cassini , also known as Jean-Dominique Cassini (8 June 1625 – 14 September 1712)

1001-463: A roughly 400 km radius rocky core surrounded by a roughly 160 km envelope of H 2 O, mainly in the form of water ice, but with some models suggesting that the lowermost part of this layer could be in the form of an internal liquid salt water ocean (a situation similar to that of its orbital resonance partner, Enceladus ). Downward bending of the surface associated with the 1.5 km high ridge Janiculum Dorsa can most easily be explained by

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1092-451: A sedimentary rock. Sedimentary rocks are mainly divided into four categories: sandstone, shale, carbonate, and evaporite. This group of classifications focuses partly on the size of sedimentary particles (sandstone and shale), and partly on mineralogy and formation processes (carbonation and evaporation). Igneous and sedimentary rocks can then be turned into metamorphic rocks by heat and pressure that change its mineral content, resulting in

1183-499: A single environment and do not necessarily occur in a single order. The Hawaiian Islands , for example, consist almost entirely of layered basaltic lava flows. The sedimentary sequences of the mid-continental United States and the Grand Canyon in the southwestern United States contain almost-undeformed stacks of sedimentary rocks that have remained in place since Cambrian time. Other areas are much more geologically complex. In

1274-557: A source of heat for Enceladus's extensive geological activity, which shows up most dramatically in its cryovolcanic geyser-like jets . The resonance also maintains a smaller eccentricity in Dione's orbit (0.0022), tidally heating it as well. Dione has two co-orbital, or trojan , moons, Helene and Polydeuces . They are located within Dione's Lagrangian points L 4 and L 5 , 60 degrees ahead of and behind Dione respectively. A leading co-orbital moon twelve degrees ahead of Helene

1365-510: A thin layer of molecular oxygen ions ( O 2 ) around Dione, so thin that scientists prefer to call it an exosphere rather than a tenuous atmosphere. The density of molecular oxygen ions determined from the Cassini plasma spectrometer data ranges from 0.01 to 0.09 per cm. The Cassini probe instruments were unable to directly detect water from the exosphere due to high background levels, but it seems that highly charged particles from

1456-400: A variety of applications. Dating of lava and volcanic ash layers found within a stratigraphic sequence can provide absolute age data for sedimentary rock units that do not contain radioactive isotopes and calibrate relative dating techniques. These methods can also be used to determine ages of pluton emplacement. Thermochemical techniques can be used to determine temperature profiles within

1547-400: A world riven by enormous fractures on its trailing hemisphere. The Cassini orbiter performed a closer flyby of Dione at 500 km (310 mi) on 11 October 2005, and captured oblique images of the cliffs, showing that some of them are several hundred metres high. Dione features linear 'virgae' that are up to hundreds of km long but less than 5 km wide. These lines run parallel to

1638-419: Is a branch of natural science concerned with the Earth and other astronomical objects , the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth sciences , including hydrology . It is integrated with Earth system science and planetary science . Geology describes the structure of the Earth on and beneath its surface and

1729-422: Is accomplished in two primary ways: through faulting and folding . In the shallow crust, where brittle deformation can occur, thrust faults form, which causes the deeper rock to move on top of the shallower rock. Because deeper rock is often older, as noted by the principle of superposition , this can result in older rocks moving on top of younger ones. Movement along faults can result in folding, either because

1820-460: Is an intimate coupling between the movement of the plates on the surface and the convection of the mantle (that is, the heat transfer caused by the slow movement of ductile mantle rock). Thus, oceanic parts of plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is actually the rigid upper thermal boundary layer of the convecting mantle. This coupling between rigid plates moving on

1911-464: Is heavily cratered and is uniformly bright. Its trailing hemisphere, however, contains an unusual and distinctive surface feature: a network of bright ice cliffs. Scientists recognise Dionean geological features of the following types: When the Voyager space probe photographed Dione in 1980, it showed what appeared to be wispy features covering its trailing hemisphere. The origin of these features

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2002-433: Is horizontal). The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of the vertical timeline, a partial or complete record of the time elapsed from deposition of

2093-616: Is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources , understanding natural hazards , remediating environmental problems, and providing insights into past climate change . Geology is a major academic discipline , and it is central to geological engineering and plays an important role in geotechnical engineering . The majority of geological data comes from research on solid Earth materials. Meteorites and other extraterrestrial natural materials are also studied by geological methods. Minerals are naturally occurring elements and compounds with

2184-484: Is primarily accomplished through normal faulting and through the ductile stretching and thinning. Normal faults drop rock units that are higher below those that are lower. This typically results in younger units ending up below older units. Stretching of units can result in their thinning. In fact, at one location within the Maria Fold and Thrust Belt , the entire sedimentary sequence of the Grand Canyon appears over

2275-568: Is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." The principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock , it can be determined that the igneous intrusion is younger than the sedimentary rock. Different types of intrusions include stocks, laccoliths , batholiths , sills and dikes . The principle of cross-cutting relationships pertains to

2366-523: Is used for geologically young materials containing organic carbon . The geology of an area changes through time as rock units are deposited and inserted, and deformational processes alter their shapes and locations. Rock units are first emplaced either by deposition onto the surface or intrusion into the overlying rock . Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows blanket

2457-578: The Galilean satellites as a clock. In 1683, Cassini presented the correct explanation of the phenomenon of zodiacal light . Zodiacal light is a faint glow that extends away from the Sun in the ecliptic plane of the sky, caused by dusty objects in interplanetary space. Cassini is also credited with introducing Indian Astronomy to Europe. In 1688, the French envoy to Siam (Thailand), Simon de la Loubère , returned to Paris with an obscure manuscript relating to

2548-489: The Po River . "Cassini composed several memoirs on the flooding of the Po River and on the means of avoiding it; moreover, he also carried out experiments in applied hydraulics." In 1663 he was named superintendent of fortifications and in 1665 inspector for Perugia . The Pope asked Cassini to take Holy Orders to work with him permanently but Cassini turned him down because he wanted to work on astronomy full-time. In

2639-506: The bedrock . This study is often known as Quaternary geology , after the Quaternary period of geologic history, which is the most recent period of geologic time. Magma is the original unlithified source of all igneous rocks . The active flow of molten rock is closely studied in volcanology , and igneous petrology aims to determine the history of igneous rocks from their original molten source to their final crystallization. In

2730-512: The geochemical evolution of rock units. Petrologists can also use fluid inclusion data and perform high temperature and pressure physical experiments to understand the temperatures and pressures at which different mineral phases appear, and how they change through igneous and metamorphic processes. This research can be extrapolated to the field to understand metamorphic processes and the conditions of crystallization of igneous rocks. This work can also help to explain processes that occur within

2821-402: The mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that. More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan . These images have led to a much more detailed view of the interior of the Earth, and have replaced

Dione (moon) - Misplaced Pages Continue

2912-596: The 1670s, Cassini began work on a project to create a topographic map of France, using Gemma Frisius 's technique of triangulation . The project was continued by his son Jacques Cassini and eventually finished by his grandson César-François Cassini de Thury and published as the Carte de Cassini in 1789 or 1793. It was the first topographic map of an entire country . Geology Geology (from Ancient Greek γῆ ( gê )  'earth' and λoγία ( -logía )  'study of, discourse')

3003-440: The 1960s, it was discovered that the Earth's lithosphere , which includes the crust and rigid uppermost portion of the upper mantle , is separated into tectonic plates that move across the plastically deforming, solid, upper mantle, which is called the asthenosphere . This theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity. There

3094-759: The Cape of Good Hope, suggesting that the names of the Titans (sisters and brothers of Cronus ) be used. Dione orbits Saturn with a semimajor axis about 2% less than that of the Moon . However, reflecting Saturn 's greater mass (95 times that of Earth), Dione's orbital period is one tenth that of the Moon. Dione is currently in a 1:2 mean-motion orbital resonance with moon Enceladus , completing one orbit of Saturn for every two orbits completed by Enceladus. This resonance maintains Enceladus's orbital eccentricity (0.0047), providing

3185-548: The Earth was elongated at its poles. More than forty years of controversy about the subject were closed in favour of Newton's theory after the measurements of the French Geodesic Mission (1736 to 1744) and the Lapponian expedition in 1737 led by Pierre Louis Moreau de Maupertuis Cassini was also the first to make successful measurements of longitude by the method suggested by Galileo , using eclipses of

3276-424: The Earth, such as subduction and magma chamber evolution. Structural geologists use microscopic analysis of oriented thin sections of geological samples to observe the fabric within the rocks, which gives information about strain within the crystalline structure of the rocks. They also plot and combine measurements of geological structures to better understand the orientations of faults and folds to reconstruct

3367-484: The Grand Canyon in the southwestern United States being a very visible example, the lower rock units were metamorphosed and deformed, and then deformation ended and the upper, undeformed units were deposited. Although any amount of rock emplacement and rock deformation can occur, and they can occur any number of times, these concepts provide a guide to understanding the geological history of an area. Geologists use

3458-586: The Marquis Cornelio Malvasia , a senator of Bologna with a great interest in astrology, invited Cassini to Bologna and offered him a position in the Panzano Observatory, which he was constructing at that time. Most of their time was spent calculating newer, better, and more accurate ephemerides for astrological purposes using the rapidly advancing astronomical methods and tools of the day. In 1653, Cassini, wishing to employ

3549-535: The San Petronio Basilica , moving the pinhole gnomon that projected the Sun's image up into the church's vaults 66.8 meters (219 ft) away from the meridian inscribed in the floor. The much larger image of the Sun's disk projected by the camera obscura effect allowed him to measure the change in diameter of the Sun's disk over the year as the Earth moved toward and then away from the Sun. He concluded

3640-608: The astronomical traditions of that country, along with a French translation. The Siamese Manuscript, as it is now called, somehow fell into Cassini's hands. He was intrigued enough by it to spend considerable time and effort deciphering its cryptic contents, also determining on the way that the document originated in India. His explication of the manuscript appeared in La Loubère's book on the Kingdom of Siam in 1691, . Attracted to

3731-537: The beginning of the 20th century, advancement in geological science was facilitated by the ability to obtain accurate absolute dates to geological events using radioactive isotopes and other methods. This changed the understanding of geological time. Previously, geologists could only use fossils and stratigraphic correlation to date sections of rock relative to one another. With isotopic dates, it became possible to assign absolute ages to rock units, and these absolute dates could be applied to fossil sequences in which there

Dione (moon) - Misplaced Pages Continue

3822-400: The bright albedo of the leading side suggests that Dione has remained in its current orientation for several billion years. Like Callisto , Dione's craters lack the high-relief features seen on the Moon and Mercury ; this is probably due to slumping of the weak icy crust over geologic time. On 7 April 2010, instruments on board the uncrewed Cassini probe , which flew by Dione, detected

3913-638: The changes in size he measured were consistent with Johannes Kepler 's 1609 heliocentric theory, where the Earth was moving around the Sun in an elliptical orbit instead of the Ptolemaic system where the Sun orbited the Earth in an eccentric orbit. Cassini remained in Bologna working until Colbert recruited him to come to Paris to help set up the Paris Observatory . Cassini departed from Bologna on 25 February 1669. Cassini's determinations of

4004-515: The creation of topographic gradients, causing material on the rock unit that is increasing in elevation to be eroded by hillslopes and channels. These sediments are deposited on the rock unit that is going down. Continual motion along the fault maintains the topographic gradient in spite of the movement of sediment and continues to create accommodation space for the material to deposit. Deformational events are often also associated with volcanism and igneous activity. Volcanic ashes and lavas accumulate on

4095-437: The crust, the uplift of mountain ranges, and paleo-topography. Fractionation of the lanthanide series elements is used to compute ages since rocks were removed from the mantle. Other methods are used for more recent events. Optically stimulated luminescence and cosmogenic radionuclide dating are used to date surfaces and/or erosion rates. Dendrochronology can also be used for the dating of landscapes. Radiocarbon dating

4186-578: The discovery of the Great Red Spot on Jupiter (ca. 1665). Around 1690, Cassini was the first to observe differential rotation within Jupiter's atmosphere . In 1672 he sent his colleague Jean Richer to Cayenne , French Guiana, while he himself stayed in Paris. The two made simultaneous observations of Mars and, by computing the parallax , determined its distance from Earth. This allowed for

4277-859: The equator and are only apparent at lower latitudes (at less than 45° north or south); similar features are noted on Rhea . They are brighter than everything around them and appear to overlay other features such as ridges and craters, indicating they are relatively young. It has been proposed that these lines are of exogenic origin, as the result of the emplacement of material across the surface by low‐velocity impacts of material sourced from Saturn's rings, co‐orbital moons, or closely approaching comets. Dione's icy surface includes heavily cratered terrain, moderately cratered plains, lightly cratered plains, and areas of tectonic fractures. The heavily cratered terrain has numerous craters greater than 100 kilometres (62 mi) in diameter. The plains areas tend to have craters less than 30 kilometres (19 mi) in diameter. Some of

4368-418: The expected dual role yet focusing the overwhelming majority of his time on astronomy rather than the astrology he had studied so much in his youth. Cassini thoroughly adopted his new country, to the extent that he became interchangeably known as Jean-Dominique Cassini, although that is also the name of his great-grandson, Dominique, comte de Cassini . During this time, Cassini's method of determining longitude

4459-570: The fault is a normal fault or a thrust fault . The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts ) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in

4550-403: The faults are not planar or because rock layers are dragged along, forming drag folds as slip occurs along the fault. Deeper in the Earth, rocks behave plastically and fold instead of faulting. These folds can either be those where the material in the center of the fold buckles upwards, creating " antiforms ", or where it buckles downwards, creating " synforms ". If the tops of the rock units within

4641-616: The first time an estimation of the dimensions of the Solar System : since the relative ratios of various Sun-planet distances were already known from geometry, only a single absolute interplanetary distance was needed to calculate all of the distances. In 1677, the English philosopher John Locke visited Cassini in Paris. He writes, "At the Observatory, we saw the Moon in a twenty-two foot glass, and Jupiter, with his satellites, in

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4732-483: The folds remain pointing upwards, they are called anticlines and synclines , respectively. If some of the units in the fold are facing downward, the structure is called an overturned anticline or syncline, and if all of the rock units are overturned or the correct up-direction is unknown, they are simply called by the most general terms, antiforms, and synforms. Even higher pressures and temperatures during horizontal shortening can cause both folding and metamorphism of

4823-404: The formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether

4914-407: The four moons he discovered ( Tethys , Dione, Rhea , and Iapetus ) Sidera Lodoicea ("the stars of Louis") to honor king Louis XIV . Cassini found Dione in 1684 using a large aerial telescope he set up on the grounds of the Paris Observatory . The satellites of Saturn were not named until 1847, when William Herschel 's son John Herschel published Results of Astronomical Observations made at

5005-579: The geological history of the Earth as a whole. One aspect is to demonstrate the age of the Earth . Geology provides evidence for plate tectonics , the evolutionary history of life , and the Earth's past climates . Geologists broadly study the properties and processes of Earth and other terrestrial planets. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including fieldwork , rock description , geophysical techniques , chemical analysis , physical experiments , and numerical modelling . In practical terms, geology

5096-487: The heavens in his youth, his first interest was in astrology . While young he read widely on the subject of astrology, and soon was very knowledgeable about it; this extensive knowledge of astrology led to his first appointment as an astronomer. Later in life he focused almost exclusively on astronomy and all but denounced astrology as he became increasingly involved in the Scientific Revolution . In 1645

5187-431: The internal activity and resurfacing ceased, cratering continued primarily on the leading hemisphere and wiped out the streak patterns there. This hypothesis was proven wrong by the Cassini probe flyby of 13 December 2004, which produced close-up images. These revealed that the 'wisps' were, in fact, not ice deposits at all, but rather bright ice cliffs created by tectonic fractures (chasmata). Dione has been revealed as

5278-423: The internal composition and structure of the Earth. Seismologists can use the arrival times of seismic waves to image the interior of the Earth. Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core . These advances led to the development of a layered model of the Earth, with a lithosphere (including crust) on top,

5369-464: The later end of the scale, it is marked by the present day (in the Holocene epoch ). The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in

5460-454: The lowest layer to deposition of the highest bed. The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist during the same period throughout the world, their presence or (sometimes) absence provides a relative age of the formations where they appear. Based on principles that William Smith laid out almost a hundred years before the publication of Charles Darwin 's theory of evolution ,

5551-497: The mantle and show the crystallographic structures expected in the inner core of the Earth. The geological time scale encompasses the history of the Earth. It is bracketed at the earliest by the dates of the first Solar System material at 4.567 Ga (or 4.567 billion years ago) and the formation of the Earth at 4.54 Ga (4.54 billion years), which is the beginning of the Hadean eon  – a division of geological time. At

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5642-405: The matrix. As a result, xenoliths are older than the rock that contains them. The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units

5733-412: The plains are more heavily cratered than others. Much of the heavily cratered terrain is located on the trailing hemisphere, with the less cratered plains areas present on the leading hemisphere. This is the opposite of what some scientists expected; Shoemaker and Wolfe proposed a cratering model for a tidally locked satellite with the highest cratering rates on the leading hemisphere and the lowest on

5824-428: The planet's powerful radiation belts could split the water in the ice into hydrogen and oxygen. Dione was first imaged by the Voyager space probes. It has also been probed five times from close distances by the Cassini orbiter . There was a close targeted flyby at a distance of 500 km (310 mi) on 11 October 2005; another flyby was performed on 7 April 2010, also at a distance of 500 km. A third flyby

5915-517: The presence of such an ocean. Neither moon has a shape close to hydrostatic equilibrium ; the deviations are maintained by isostasy . Dione's ice shell is thought to vary in thickness by less than 5%, with the thinnest areas at the poles, where tidal heating of the crust is greatest. Though somewhat smaller and denser, Dione is otherwise very similar to Rhea . They both have similar albedo features and varied terrain, and both have dissimilar leading and trailing hemispheres . Dione's leading hemisphere

6006-413: The primary record of the majority of the geological history of the Earth. There are three major types of rock: igneous , sedimentary , and metamorphic . The rock cycle illustrates the relationships among them (see diagram). When a rock solidifies or crystallizes from melt ( magma or lava ), it is an igneous rock . This rock can be weathered and eroded , then redeposited and lithified into

6097-539: The principal chair of astronomy at the University of Bologna . While in his position in Bologna, he observed and wrote a treatise on the comet of 1652 . He was also employed by the senate of Bologna as a hydraulic engineer , and appointed by Pope Alexander VII inspector of fortifications in 1657. He was subsequently director of waterways in the papal states. In San Petronio, Bologna, Cassini convinced church officials to create an improved sundial meridian line at

6188-569: The principles of succession developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, localization of fossil types due to lateral changes in habitat ( facies change in sedimentary strata), and that not all fossils formed globally at the same time. Geologists also use methods to determine the absolute age of rock samples and geological events. These dates are useful on their own and may also be used in conjunction with relative dating methods or to calibrate relative methods. At

6279-423: The processes that have shaped that structure. Geologists study the mineralogical composition of rocks in order to get insight into their history of formation. Geology determines the relative ages of rocks found at a given location; geochemistry (a branch of geology) determines their absolute ages . By combining various petrological, crystallographic, and paleontological tools, geologists are able to chronicle

6370-428: The rocks. This metamorphism causes changes in the mineral composition of the rocks; creates a foliation , or planar surface, that is related to mineral growth under stress. This can remove signs of the original textures of the rocks, such as bedding in sedimentary rocks, flow features of lavas , and crystal patterns in crystalline rocks . Extension causes the rock units as a whole to become longer and thinner. This

6461-537: The rotational periods of Jupiter and Mars in 1665–1667 enhanced his fame, and in 1669, with the reluctant assent of the Pope, he moved to France and through a grant from Louis XIV of France helped to set up the Paris Observatory , which opened in 1671; he would remain the director of the observatory for the rest of his career until his death in 1712. For the remaining forty-one years of his life Cassini served as astronomer/astrologer to Louis XIV ("The Sun King"); serving

6552-471: The same. The most remote was on the east, and the other three on the west. We also saw Saturn and his rings, in a twelve-foot glass, and one of his satellites." Cassini initially held the Earth to be the centre of the Solar System, though later observations compelled him to accept the model of the Solar System proposed by Nicolaus Copernicus , and eventually that of Tycho Brahe . "In 1659 he presented

6643-433: The simplified layered model with a much more dynamic model. Mineralogists have been able to use the pressure and temperature data from the seismic and modeling studies alongside knowledge of the elemental composition of the Earth to reproduce these conditions in experimental settings and measure changes within the crystal structure. These studies explain the chemical changes associated with the major seismic discontinuities in

6734-532: The southwestern United States, sedimentary, volcanic, and intrusive rocks have been metamorphosed, faulted, foliated, and folded. Even older rocks, such as the Acasta gneiss of the Slave craton in northwestern Canada , the oldest known rock in the world have been metamorphosed to the point where their origin is indiscernible without laboratory analysis. In addition, these processes can occur in stages. In many places,

6825-550: The subsurface. Sub-specialities of geology may distinguish endogenous and exogenous geology. Geological field work varies depending on the task at hand. Typical fieldwork could consist of: In addition to identifying rocks in the field ( lithology ), petrologists identify rock samples in the laboratory. Two of the primary methods for identifying rocks in the laboratory are through optical microscopy and by using an electron microprobe . In an optical mineralogy analysis, petrologists analyze thin sections of rock samples using

6916-407: The surface of the Earth and the convecting mantle is called plate tectonics . The development of plate tectonics has provided a physical basis for many observations of the solid Earth . Long linear regions of geological features are explained as plate boundaries: Plate tectonics has provided a mechanism for Alfred Wegener 's theory of continental drift , in which the continents move across

7007-488: The surface of the Earth over geological time. They also provided a driving force for crustal deformation, and a new setting for the observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle. Advances in seismology , computer modeling , and mineralogy and crystallography at high temperatures and pressures give insights into

7098-479: The surface, and igneous intrusions enter from below. Dikes , long, planar igneous intrusions, enter along cracks, and therefore often form in large numbers in areas that are being actively deformed. This can result in the emplacement of dike swarms , such as those that are observable across the Canadian shield, or rings of dikes around the lava tube of a volcano. All of these processes do not necessarily occur in

7189-742: The surface. Igneous intrusions such as batholiths , laccoliths , dikes , and sills , push upwards into the overlying rock, and crystallize as they intrude. After the initial sequence of rocks has been deposited, the rock units can be deformed and/or metamorphosed . Deformation typically occurs as a result of horizontal shortening, horizontal extension , or side-to-side ( strike-slip ) motion. These structural regimes broadly relate to convergent boundaries , divergent boundaries , and transform boundaries, respectively, between tectonic plates. When rock units are placed under horizontal compression , they shorten and become thicker. Because rock units, other than muds, do not significantly change in volume , this

7280-407: The third timeline, the most recent period is expanded in the fourth timeline, and the most recent epoch is expanded in the fifth timeline. Horizontal scale is Millions of years (above timelines) / Thousands of years (below timeline) Epochs: Methods for relative dating were developed when geology first emerged as a natural science . Geologists still use the following principles today as

7371-438: The trailing hemisphere. This suggests that during the period of heavy bombardment, Dione was tidally locked to Saturn in the opposite orientation. Because Dione is relatively small, an impact causing a 35 kilometer crater could have spun the satellite. Because there are many craters larger than 35 kilometres (22 mi), Dione could have been repeatedly spun during its early heavy bombardment. The pattern of cratering since then and

7462-404: The use of a meridian line, sketched a plan for a new and larger meridian line but one that would be difficult to build. His calculations were precise; the construction succeeded perfectly; and its success gave Cassini a brilliant reputation for working with engineering and structural works. Cassini was employed by Pope Clement IX in regard to fortifications , river management , and flooding of

7553-495: The younger, Jacques Cassini , succeeded him as astronomer and geodesist under the name of Cassini II." In 1711 Cassini went blind and he died on 14 September 1712 in Paris at the age of 87. Cassini observed and published surface markings on Mars (earlier seen by Christiaan Huygens but not published), determined the rotation periods of Mars and Jupiter , and discovered four satellites of Saturn : Iapetus and Rhea in 1671 and 1672, and Tethys and Dione (1684). Cassini

7644-408: Was also the first of his family to begin work on the project of creating a topographic map of France. In addition, Cassini also created the first scientific map of the moon. The Cassini space probe , launched in 1997, was named after him and became the fourth to visit Saturn and the first to orbit it. Cassini was the son of Jacopo Cassini, a Tuscan, and Giulia Crovesi. In 1648 Cassini accepted

7735-655: Was an Italian (naturalised French) mathematician , astronomer , astrologer and engineer . Cassini was born in Perinaldo , near Imperia , at that time in the County of Nice , part of the Savoyard state . Cassini is known for his work on astronomy and engineering. He discovered four satellites of Saturn and noted the division of its rings; the Cassini Division was named after him. Giovanni Domenico Cassini

7826-615: Was datable material, converting the old relative ages into new absolute ages. For many geological applications, isotope ratios of radioactive elements are measured in minerals that give the amount of time that has passed since a rock passed through its particular closure temperature , the point at which different radiometric isotopes stop diffusing into and out of the crystal lattice . These are used in geochronologic and thermochronologic studies. Common methods include uranium–lead dating , potassium–argon dating , argon–argon dating and uranium–thorium dating . These methods are used for

7917-492: Was mysterious, because all that was known was that the material has a high albedo and is thin enough that it does not obscure the surface features underneath. One hypothesis was that shortly after its formation Dione was geologically active, and some process such as cryovolcanism resurfaced much of its surface, with the streaks forming from eruptions along cracks in the Dionean surface that fell back as snow or ash. Later, after

8008-502: Was performed on 12 December 2011 at a distance of 99 km (62 mi). The following flyby was on 16 June 2015 at a distance of 516 km (321 mi), and the last Cassini flyby was performed on 17 August 2015 at a distance of 474 km (295 mi). In May 2013, it was announced that NASA's spacecraft Cassini had provided scientists with evidence that Dione is more active than previously realized. Using topographic data, NASA teams deduced that crustal depression associated with

8099-448: Was reported by Stephen P. Synnott in 1982. At 1,122 km (697 mi) in diameter, Dione is the 15th largest moon in the Solar System, and is more massive than all known moons smaller than itself combined. It is also Saturn's fourth-largest moon. Based on its density, Dione’s interior is likely a combination of silicate rock and water ice in nearly equal parts by mass. Shape and gravity observations collected by Cassini suggest

8190-416: Was the first to observe these four moons , which he called Sidera Lodoicea (the stars of Louis), including Iapetus , whose anomalous variations in brightness he correctly ascribed as being due to the presence of dark material on one hemisphere (now called Cassini Regio in his honour). In addition he discovered the Cassini Division in the rings of Saturn (1675). He shares credit with Robert Hooke for

8281-459: Was used to measure the size of France accurately for the first time. The country turned out to be considerably smaller than expected, and the king quipped that Cassini had taken more of his kingdom from him than he had won in all his wars. On 14 July 1673 Cassini obtained the benefits of French citizenship. In 1674 he married Geneviève de Laistre, the daughter of the lieutenant general of the comté of Clermont. "From this marriage Cassini had two sons;

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