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105-781: Geologically separated from the Lesser Antilles by the Anegada Passage and from the Greater Antilles by the Mona passage , all the islands except for Saint Croix lie on the same carbonate platform and insular shelf , known as the Puerto Rico Bank , and same tectonic plate , known as the Puerto Rico–Virgin Islands microplate . Politically, the islands fall into three jurisdictions :

210-535: 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

315-485: 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

420-522: A change to RHT, but, a few years later, the government ordered it and it occurred on Sunday, 3 September 1967 at 5 am. The accident rate then dropped sharply, but soon rose to near its original level. The day was known as Högertrafikomläggningen, or Dagen H for short. When Iceland switched to RHT the following year, it was known as Hægri dagurinn or H-dagurinn ("The H-Day"). Most passenger cars in Iceland were already LHD. The United Kingdom

525-689: A clear view of other vehicles. The first keep-right law for driving in the United States was passed in 1792 and applied to the Philadelphia and Lancaster Turnpike . Massachusetts formalized RHT in 1821. However, the National Road was LHT until 1850, "long after the rest of the country had settled on the keep-right convention". Today the United States is RHT except the United States Virgin Islands , which

630-434: 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

735-627: 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

840-452: 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

945-415: A newspaper said, "The cart was near to the right hand kerb. According to the rules of the road, it should have been on the left side. In turning sharp round a right-hand corner, a driver should keep away to the opposite side." That rule was codified when the first Highway Code was written in 1936. Samoa , a former German colony, had been RHT for more than a century, but switched to LHT in 2009, making it

1050-608: 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

1155-451: 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

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1260-409: A simple traffic light to do the switch, but there are also interchanges that enable the switch while keeping up a continuous flow of traffic. There are six road border crossing points between Hong Kong and mainland China. In 2006, the daily average number of vehicle trips recorded at Lok Ma Chau was 31,100. The next largest is Man Kam To , where there is no changeover system and the border roads on

1365-499: 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

1470-644: A sixth of the world's land area, a quarter of its roads, and about a third of its population. In 1919, 104 of the world's territories were LHT and an equal number were RHT. Between 1919 and 1986, 34 of the LHT territories switched to RHT. While many of the countries using LHT were part of the British Empire , others such as Indonesia , Japan , Nepal , Bhutan , Macao , Thailand , Mozambique , Suriname , Sweden and Iceland (which use RHT since September 1967 and late May 1968 respectively) were not. Most of

1575-470: A ten- shilling fine to anyone not driving or riding on the left side of the road within the county of the city of Dublin , and required the local road overseers to erect written or printed notices informing road users of the law. The Road in Down and Antrim Act 1798 (38 Geo. 3. c. 28 (I)) required drivers on the road from Dublin to Donadea to keep to the left. This time, the punishment was ten shillings if

1680-400: 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

1785-606: Is LHT like many neighbouring islands. Some special-purpose vehicles in the United States, like certain postal service trucks, garbage trucks, and parking-enforcement vehicles, are built with the driver's seat on the right for safer and easier access to the curb. A common example is the Grumman LLV , which is used nationwide by the US Postal Service and by Canada Post . In Canada, the provinces of Quebec and Ontario were always RHT because they were created out of

1890-693: Is LHT, but two of its overseas territories , Gibraltar and the British Indian Ocean Territory , are RHT. In the late 1960s, the British Department for Transport considered switching to RHT, but declared it unsafe and too costly for such a built-up nation. Road building standards, for motorways in particular, allow asymmetrically designed road junctions, where merge and diverge lanes differ in length. Today, four countries in Europe continue to use LHT, all island nations:

1995-419: 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

2100-422: 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

2205-460: 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

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2310-433: 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

2415-616: 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

2520-484: 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

2625-434: Is still geared to LHT as its neighbours India, Bangladesh and Thailand use LHT. Most cars are used RHD vehicles imported from Japan. Afghanistan was LHT until the 1950s, in line with Pakistan (former part of British India). Although Portuguese Timor (present-day East Timor ), which shares the island of Timor with Indonesia , who is LHT, switched to RHT with Portugal in 1928, it switched back to LHT in 1976 during

2730-568: 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

2835-426: Is the opposite: traffic keeps right, the driver usually sits on the left side of the car (LHD: left-hand drive), and roundabouts circulate anticlockwise. In most countries, rail traffic follows the handedness of the roads; but many of the countries that switched road traffic from LHT to RHT did not switch their trains. Boat traffic on bodies of water is RHT, regardless of location. Boats are traditionally piloted from

2940-523: 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

3045-721: The Spanish Virgin Islands or Puerto Rican Virgin Islands. Christopher Columbus named the islands after Saint Ursula and the 11,000 Virgins ( Spanish : Santa Úrsula y las Once Mil Vírgenes ), shortened to the Virgins ( las Vírgenes ). The official name of the British territory is the Virgin Islands, and the official name of the U.S. territory is the Virgin Islands of the United States. In practice,

3150-634: The British Virgin Islands , and the United States Virgin Islands are LHD due to their being imported from the United States. Brazil , a Portuguese colony until the early 19th century, had in the 19th and the early 20th century mixed rules, with some regions still on LHT, switching these remaining regions to RHT in 1928, the same year Portugal switched sides. Other Central and South American countries that later switched from LHT to RHT include Argentina, Chile, Panama, Paraguay, and Uruguay. Suriname , along with neighbouring Guyana , are

3255-592: The Cape Colony (present-day South Africa and Lesotho ), as well as in British West Africa (present-day Ghana, Gambia, Sierra Leone and Nigeria); former British West Africa, however, has now switched to RHT, as all its neighbours, which are former French colonies, use RHT. South Africa, formerly the Cape Colony, introduced LHT in former German South West Africa , present-day Namibia , after

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3360-561: The French Revolution . Scholars who have looked for documentary evidence of this story have found none, and contemporary sources have not surfaced, as of 1999. In 1827, long after Napoleon's reign, Edward Planta wrote that, in Paris , "The coachmen have no established rule by which they drive on the right or left of the road, but they cross and jostle one another without ceremony." Rotterdam had no fixed rules until 1917, although

3465-871: The Indonesian occupation of East Timor . In the 1930s, parts of China such as the Shanghai International Settlement , Canton and Japanese-occupied northeast China used LHT. However, in 1946 the Republic of China made RHT mandatory in China (including Taiwan ). Taiwan was LHT under Japanese colonization from 1895–1945. Portuguese Macau (present-day Macau ) remained LHT, along with British Hong Kong , despite being transferred to China in 1999 and 1997 respectively. Both North Korea and South Korea use RHT since 1946, after liberation from Japanese colonialization . The Philippines

3570-560: The Maghreb , where it is still used. Countries in these areas include Mali , Mauritania , Ivory Coast , Burkina Faso , Benin , Niger , Morocco , Algeria , and Tunisia . Other French former colonies that are RHT include Cameroon , Central African Republic , Chad , Djibouti , Gabon , and the Republic of the Congo . Rwanda and Burundi are RHT but are considering switching to LHT (see "Potential future shifts" section below). In

3675-506: 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

3780-512: 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

3885-402: 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

3990-419: The starboard side (and not the port side like RHT road traffic vehicles) to facilitate priority to the right . Historically, many places kept left, while many others kept right, often within the same country. There are many myths that attempt to explain why one or the other is preferred. About 90 percent of people are right-handed , and many explanations reference this. Horses are traditionally mounted from

4095-440: 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

4200-424: 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

4305-484: 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

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4410-1071: The Spanish Virgin Islands, vehicles are driven on the right-hand side of the road. These three form the SSS islands that with the ABC islands comprise the Dutch Caribbean , of which the BES islands are not direct Kingdom constituents but subsumed with the country of the Netherlands . Physiographically , these continental islands are not part of the volcanic Windward Islands arc, although sometimes grouped with them culturally and politically. Disputed territories administered by Guyana . Disputed territories administered by Colombia . Geology Geology (from Ancient Greek γῆ ( gê )  'earth' and λoγία ( -logía )  'study of, discourse')

4515-484: The U.S. and British Virgin Islands, and Spanish in the Puerto Rican territory. St. Thomas is the most populous island, with St. Croix close behind (51,634 and 50,601, respectively). Motor vehicles are driven on the left-hand side of the road in both the British and the U.S. Virgin Islands, although the steering wheels on most cars are located on the left side (as is the norm for drive-on-the-right localities). In

4620-545: The United Kingdom, Ireland (formerly part of the UK), Cyprus and Malta (both former British colonies). Many former British colonies in the region have always been LHT, including Australia, New Zealand, Fiji , Kiribati , Solomon Islands , Tonga , and Tuvalu ; and nations that were previously administered by Australia: Nauru and Papua New Guinea . Initially traffic was slow and very sparse, but, as early as 1856,

4725-602: The United States and Denmark (not ratified by the United States until 1917) resulted in Denmark selling the Danish Virgin Islands to the United States for $ 25 million in gold. The Virgin Islands have been under the sovereignty of several nations and groups throughout history. Below is a table which represents the affiliation of the various islands: * Largely under control of pirates . ** Coexisting claim. *** Leased/shared territory. The total population of

4830-592: The Virgin Islands is 147,778: 104,901 in the U.S. Virgin Islands, 31,758 in the British, and 11,119 in the Spanish. Roughly three-quarters of islanders are black in the British and U.S. Virgin Islands, while the majority of inhabitants in Culebra and Vieques are Puerto Rican of European descent, with a significant Afro-Puerto Rican community. The main languages are English and Virgin Islands Creole in

4935-537: 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

5040-593: The cities Milan , Turin , and Florence . In 1915, allied forces of World War I imposed LHT in areas of military operation, but this was revoked in 1918. Rome was reported by Goethe as LHT in the 1780s. Naples was also LHT although surrounding areas were often RHT. In cities, LHT was considered safer since pedestrians, accustomed to keeping right, could better see oncoming vehicular traffic. Finally, in 1923 Benito Mussolini decreed that all LHT areas would gradually transition to RHT. In spite of this, some Italian heavy commercial vehicles were right-hand drive until

5145-517: The countries that were part of the French colonial empire adopted RHT. Historical switches of traffic handedness have often been motivated by factors such as changes in political administration, a desire for uniformity within a country or with neighboring states, or availability and affordability of vehicles. In LHT, traffic keeps left and cars usually have the steering wheel on the right (RHD: right-hand drive) and roundabouts circulate clockwise. RHT

5250-419: The country. In a study of the ancient traffic system of Pompeii , Eric Poehler was able to show that drivers of carts drove in the middle of the road whenever possible. This was the case even on roads wide enough for two lanes. The wear marks on the kerbstones, however, prove that when there were two lanes of traffic, and the volume of traffic made it necessary to divide the lanes, the drivers always drove on

5355-515: 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

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5460-437: 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

5565-490: The easternmost British overseas territory of the Virgin Islands , informally referred to as the British Virgin Islands , the central unincorporated American territory of the Virgin Islands of the United States , commonly known as the U.S. Virgin Islands, and the westernmost island-municipalities of the unincorporated American territory of Puerto Rico, officially named Vieques and Culebra but generally called

5670-629: The end of World War I . Sudan, formerly part of Anglo-Egyptian Sudan , switched to RHT in 1973. Most of its neighbours were RHT countries, with the exception of Uganda and Kenya, but since the independence of South Sudan in 2011, all of its neighbours drive on the right (including South Sudan, despite its land borders with two LHT countries). Although Portugal switched to RHT in 1928, its colony of Mozambique remained LHT because it has land borders with former British colonies (with LHT). France introduced RHT in French West Africa and

5775-584: The enslaved people remain the bulk of the population, sharing a common African-Caribbean heritage with the rest of the English-speaking Caribbean . Like mainland Puerto Rico, the Virgin Islands that belonged to Spain were ceded to the United States in 1898. The United States took possession of the islands after the signing of the armistice that put an end to military operations in the Spanish–American War . A 1916 treaty between

5880-570: 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

5985-403: 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

6090-558: The first territory in almost 30 years to change sides. The move was legislated in 2008 to allow Samoans to use cheaper vehicles imported from Australia, New Zealand, or Japan, and to harmonise with other South Pacific nations. A political party, The People's Party , was formed by the group People Against Switching Sides (PASS) to protest against the change, with PASS launching a legal challenge; in April 2008 an estimated 18,000 people attended demonstrations against switching. The motor industry

6195-483: 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

6300-570: The following were declared public holidays, to reduce traffic. The change included a three-day ban on alcohol sales, while police mounted dozens of checkpoints, warning drivers to drive slowly. Rwanda and Burundi , former Belgian colonies in Central Africa , are RHT but are considering switching to LHT like neighbouring members of the East African Community (EAC). A survey in 2009 found that 54% of Rwandans favoured

6405-404: 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

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6510-577: The former Austrian Partition changed in the 1920s. Croatia-Slavonia switched on joining the Kingdom of Yugoslavia in 1918, although Istria and Dalmatia were already RHT. The switch in Czechoslovakia from LHT to RHT had been planned for 1939, but was accelerated by the start of the German occupation of Czechoslovakia that year. Similarly, Hungary switched in 1941. West Ukraine was LHT, but

6615-496: The former French colony of New France . The province of British Columbia changed to RHT in stages from 1920 to 1923, New Brunswick , Nova Scotia , and Prince Edward Island in 1922, 1923, and 1924 respectively, and the British colony of Newfoundland (part of Canada since 1949) in 1947, in order to allow traffic (without side switch) to or from the United States. In the West Indies , colonies and territories drive on

6720-579: 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

6825-402: The history of rock deformation in the area. In addition, they perform analog and numerical experiments of rock deformation in large and small settings. Right- and left-hand traffic This is an accepted version of this page Left-hand traffic ( LHT ) and right-hand traffic ( RHT ) are the practices, in bidirectional traffic , of keeping to the left side and to the right side of

6930-423: 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,

7035-400: The late 18th century, right-hand traffic started to be introduced in the United States of America based on teamsters ' use of large freight wagons pulled by several pairs of horses and without a driver's seat; the (typically right-handed) postilion held his whip in his right hand and thus sat on the left rear horse, and therefore preferred other wagons passing on the left so that he would have

7140-464: 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

7245-526: The left, and led from the left, with the reins in the right hand. So people walking horses might use RHT, to keep the animals separated. Also referenced is the need for pedestrians to keep their swords in the right hand and pass on the left as in LHT, for self-defence. It has been suggested that wagon-drivers whipped their horses with their right hand, and thus sat on the left-hand side of the wagon, as in RHT. Academic Chris McManus notes that writers have stated that in

7350-454: 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 ,

7455-497: 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

7560-405: 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

7665-474: The offender was not the owner of the vehicle, or one Irish pound (twenty shillings) if he/she was. The Grand Juries (Ireland) Act 1836 ( 6 & 7 Will. 4 c. 116) mandated LHT for the whole country, violators to be fined up to five shillings and imprisoned in default for up to one month. An oft-repeated story is that Napoleon changed the custom from LHT to RHT in France and the countries he conquered after

7770-470: The one direction, and the side on which the vehicle in the rear overtakes the one in the front. For example, a driver in an LHT country would typically overtake on the right of the vehicle being overtaken. RHT is used in 165 countries and territories, mainly in the Americas , Continental Europe , most of Africa and mainland Asia (except South Asia ), while 75 countries use LHT, which account for about

7875-573: The only two remaining LHT countries in South America . LHT was introduced by the U.K. in British India (now India , Pakistan , Myanmar , and Bangladesh ), British Malaya and British Borneo (now Malaysia , Brunei and Singapore), as well as British Hong Kong . These countries, except Myanmar, are still LHT, as well as neighbouring countries Bhutan and Nepal . Myanmar switched to RHT in 1970, although much of its infrastructure

7980-502: The other side". It was later legislated as the London Bridge Act 1756 ( 29 Geo. 2 c. 40), which required that "all carriages passing over the said bridge from London shall go on the east side thereof" – those going south to remain on the east, i.e. the left-hand side by direction of travel. This may represent the first statutory requirement for LHT. In the Kingdom of Ireland , a law of 1793 (33 Geo. 3. c. 56 (I)) provided

8085-413: 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

8190-569: 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

8295-423: 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

8400-592: The rest of Ukraine, having been part of the Russian Empire, was RHT. In Italy, it had been decreed in 1901 that each province define its own traffic code , including the handedness of traffic, and the 1903 Baedeker guide reported that the rule of the road varied by region. For example, in Northern Italy , the provinces of Brescia , Como , Vicenza , and Ravenna were RHT while nearby provinces of Lecco , Verona , and Varese were LHT, as were

8505-774: The rest of the Netherlands was RHT. In May 1917 the police in Rotterdam ended traffic chaos by enforcing right hand traffic. In Russia, in 1709, the Danish envoy under Tsar Peter the Great noted the widespread custom for traffic in Russia to pass on the right, but it was only in 1752 that Empress Elizabeth officially issued an edict for traffic to keep to the right. After the Austro-Hungarian Empire broke up,

8610-596: The resulting countries gradually changed to RHT. In Austria , Vorarlberg switched in 1921, North Tyrol in 1930, Carinthia and East Tyrol in 1935, and the rest of the country in 1938. In Romania , Transylvania , the Banat and Bukovina were LHT until 1919, while Wallachia and Moldavia were already RHT. Partitions of Poland belonging to the German Empire and the Russian Empire were RHT, while

8715-582: The right-hand side. These considerations can also be demonstrated in the archaeological findings of other cities in the Roman Empire . One of the first references in England to requiring traffic direction was an order by the London Court of Aldermen in 1669, requiring a man to be posted on London Bridge to ensure that "all cartes going to keep on the one side and all cartes coming to keep on

8820-426: The road, respectively. They are fundamental to traffic flow , and are sometimes called the rule of the road . The terms right- and left-hand drive refer to the position of the driver and the steering wheel in the vehicle and are, in automobiles, the reverse of the terms right- and left-hand traffic . The rule also includes where on the road a vehicle is to be driven, if there is room for more than one vehicle in

8925-428: 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

9030-577: The same side as their parent countries, except for the United States Virgin Islands . Many of the island nations are former British colonies and drive on the left, including Jamaica , Antigua and Barbuda , Barbados , Dominica , Grenada , Saint Kitts and Nevis , Saint Lucia , Saint Vincent and the Grenadines , Trinidad and Tobago , and The Bahamas . However, most vehicles in The Bahamas, Cayman Islands , Turks and Caicos Islands and both

9135-433: 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

9240-532: 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,

9345-550: 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

9450-407: 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

9555-488: 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

9660-479: 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

9765-742: 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

9870-464: The switch. Reasons cited were the perceived lower costs of RHD vehicles, easier maintenance and the political benefit of harmonising traffic regulations with other EAC countries. The survey indicated that RHD cars were 16% to 49% cheaper than their LHD counterparts. In 2014, an internal report by consultants to the Ministry of Infrastructure recommended a switch to LHT. In 2015, the ban on RHD vehicles

9975-407: 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

10080-769: The traffic code was changed in 1959. Portugal switched to RHT in 1928. Finland , formerly part of LHT Sweden, switched to RHT in 1858 as the Grand Duchy of Finland by Russian decree. Spain switched to RHT in 1918, but not in the entire country. In Madrid people continued to drive on the left until 1924 when a national law forced drivers in Madrid switch to RHT. Madrid Metro still uses LHT. Sweden switched to RHT in 1967, having been LHT from about 1734 despite having land borders with RHT countries Norway and Finland, and approximately 90% of cars being left-hand drive (LHD). A referendum in 1955 overwhelmingly rejected

10185-640: The two island groups are almost universally referred to as the British Virgin Islands and the U.S. Virgin Islands. The Virgin Islands were originally inhabited by the Arawak and Carib , many of whom are thought to have perished during the colonial period due to enslavement , foreign disease, and war brought about by European colonists. European colonists later settled here and established sugar plantations and at least one tobacco plantation, and bought slaves from Africa . The descendants of

10290-580: The year 1300, Pope Boniface VIII directed pilgrims to keep left; however, others suggest that he directed them to keep to the right, and there is no documented evidence to back either claim. The UK introduced LHT in the East Africa Protectorate (present-day Kenya ), the Protectorate of Uganda , Tanganyika (formerly part of German East Africa ; present-day Tanzania ), Rhodesia (present-day Zambia / Zimbabwe ), Eswatini and

10395-399: The year Japan's first railway was introduced, built with technical aid from the British – that this unwritten rule received official acknowledgment. Gradually, a massive network of railways and tram tracks was built, with all railway vehicles driven on the left-hand side. However, it took another half-century, until 1924, until left-hand traffic was legally mandated. Post- World War II Okinawa

10500-523: Was also opposed, as 14,000 of Samoa's 18,000 vehicles were designed for RHT and the government refused to meet the cost of conversion. After months of preparation, the switch from right to left happened in an atmosphere of national celebration. There were no reported incidents. At 05:50 local time, Monday 7 September, a radio announcement halted traffic, and an announcement at 6:00 ordered traffic to switch to LHT. The change coincided with more restrictive enforcement of speeding and seat-belt laws. That day and

10605-615: 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

10710-579: Was formalized, RHD vehicles such as public buses were still imported into the Philippines until a law passed banning the importation of RHD vehicles except in special cases. These RHD vehicles are required to be converted to LHD. Japan was never part of the British Empire, but its traffic also drives on the left. Although this practice goes back to the Edo period (1603–1868), it was not until 1872 –

10815-584: Was lifted; RHD trucks from neighbouring countries cost $ 1,000 less than LHD models imported from Europe. Although many LHT jurisdictions are on islands, there are cases where vehicles may be driven from LHT across a border into a RHT area. Such borders are mostly located in Africa and southern Asia. The Vienna Convention on Road Traffic regulates the use of foreign registered vehicles in the 78 countries that have ratified it. LHT Thailand has three RHT neighbours: Cambodia, Laos, and Myanmar. Most of its borders use

10920-661: Was mostly LHT during its Spanish and American colonial periods, as well as during the Commonwealth era . During the Japanese occupation , the Philippines remained LHT, as was required by the Japanese; but during the Battle of Manila , the liberating American forces drove their tanks to the right for easier facilitation of movement. RHT was formalized in 1945 through a decree by president Sergio Osmeña . Even though RHT

11025-949: Was ruled by the United States Civil Administration of the Ryukyu Islands until 1972, and was RHT until 6 a.m. the morning of 30 July 1978, when it switched back to LHT . The conversion operation was known as 730 ( Nana-San-Maru , which refers to the date of the changeover). Okinawa is one of only a few places to have changed from RHT to LHT in the late 20th century. While Japan drives on the left and most Japanese vehicles are RHD, imported vehicles (e.g. BMW, Mercedes-Benz, Porsche) are generally bought as LHD since LHD cars are considered to be status symbols. Vietnam became RHT as part of French Indochina , as did Laos and Cambodia . In Cambodia, RHD cars, many of which were smuggled from Thailand, were banned in 2001, even though they accounted for 80% of vehicles in

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