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Transport in Guyana

The transport sector comprises the physical infrastructure, docks and vehicle, terminals, fleets, ancillary equipment and service delivery of all the various modes of transport operating in Guyana. The transport services, transport agencies providing these services, the organizations and people who plan, build, maintain, and operate the system, and the policies that mold its development.

City transportation
Public transport around Guyana's capital Georgetown is provided by privately owned mini buses which operate in allocated zones for which there is a well-regulated fare structure. This arrangement extends to all mini bus routes throughout the country. There are designated bus stops for mini buses for most routes but some buses still pick up passengers at virtually any point on their routes. This practice often poses a serious inconvenience to other vehicles by disrupting the normal flow of traffic.

Taxis have freer movement around the city and into rural areas. Their fare, while generally standard, is less regulated. Starting in 2010, all taxis must be painted yellow, a regulation designed to protect consumers and to distinguish the vehicles from others that are often used in committing crimes. All taxis are registered under the term "Hackney Carriage" and carry the letter H at the beginning of their number plates. There are scores of taxi services operating in Georgetown but its equally easy to "flag a ride" in the central business district.

The network of routes has a number of identifiable starting points which are concentrated in the Stabroek area and along the Avenue of the Republic between Croal and Robb Streets.

Road conditions vary immensely, and maintenance is sometimes deficient. In 2006 there was one operational set of traffic lights but in July 2007, a modern system was installed by Indian firm CMS Traffic Systems Limited, through a US$2.1 million line of credit to the government from India's EXIM Bank, providing signals for both vehicular and pedestrian traffic at all major intersections in Georgetown.

Minibuses in Guyana
As of February 2016, there were 19 minibus routes in Guyana and most of them begin or are fully contained in Georgetown, Guyana.

In 2015, the Ministry of Public Works estimated that 60 percent of Guyana’s productive labour force used public transportation daily, which is widely available and fairly reliable. They also stated that the eight major bus routes, 31, 32, 40, 41, 42, 43, 44 and 45, accounted for 67 percent of the total public bus fleet in Guyana. Their survey found that 41% of commuters on the major routes were satisfied.

Long distance transportation
===Roads  === In 2004, Guyana's road network was approximately 3,995 km long, 24 percent or 940 kilometers of which comprised primary roads in the coastal and riverine areas serving the agricultural sector, while the road to Linden serves the mining and forestry sectors. 21 percent (820 kilometers) is made up of feeder roads that link the agricultural areas along the coast to the primary road network. The remaining 56 percent (2,235 kilometers) is composed of interior roads and trails. Most access roads are in poor condition. However, the Central Government has targeted several roads for complete rehabilitation, and already many have been rehabilitated.

The main coastal roads are, from west to east, the Essequibo Coast Road, the Parika to Vreed en Hoop Road, the East Coast Demerara and West Coast Berbice Roads, and the Corentyne Highway from New Amsterdam to Moleson Creek (86 kilometers). All these roads are paved and their speed limit vary between 50 and 100 km/h.

South of Georgetown the primary road is the East Bank Demerara Road, a four-lane road from Rumiveldt to Providence and two-lane from Providence to Timehri Georgetown to Timehri, where the Cheddi Jagan International Airport - Timehri (CJIAT) is located.

Between 1966 and 1968, Soesdyke, located on the East Bank Demerara Road, was connected to Mackenzie by a modern two lane highway, called the Soesdyke-Linden Highway. This road was constructed as a section of a highway connecting Georgetown with Lethem. In 1968 a bridge was built across the Demerara River at Linden, and, in 1974, it was decided that the route to Lethem would cross the Demerara River at Linden and go south, along the watershed of the Demerara and Essequibo Rivers, through Mabura, to Kurupukari. From Kurupukari it would run parallel to the old cattle trail to Annai, and from Annai it would follow an already existing road to Lethem.

In the early 1970s a two-lane road with modern geometry and surfaced with laterite was built between Linden and Rockstone. This road was later connected to Mabura and Kurupukari. In 1990-91 a two-lane laterite road was constructed between Kurupukari and Annai and a vehicle ferry installed at Kurupukari. Since there was already an existing road between Mabura and Kurupukari, and between Annai and Lethem, it was now possible for vehicles to travel between Georgetown and Lethem.

In the period 1974 to 1978, an attempt was made to build a road between Rockstone and Kurupung to facilitate the construction of a large hydroelectric station. From Rockstone it headed north to Suribanna, where a pontoon ferry was installed across the Essequibo River to Sherima. From Sherima the road went westward, intersecting the Bartica - Mahdia Road at Allsopp Point 19 mi from Bartica. From Allsopp Point the road followed the existing road towards Bartica and branched off 5 mi from Bartica going to Teperu in the lower reaches on the Mazaruni River. At Teperu a pontoon ferry was installed across the Mazaruni River to Itaballi. From Itaballi the road went westward to Peter's Mine on the Puruni River. From Peter's Mine the road continued as a penetration road to Kurupung. This road is referred to as the UMDA Road.

There is in addition a hinterland east-west main road system that extends from Kwakwani in the east, through Ituni, Linden, Rockstone, Sherima to Bartica in the west. Linden is therefore one of the main hubs for road transportation in the hinterland.

Outside the existing main roads there are several other interior roads or trails that comprise approximately 1,570 kilometers. Most of those roads are unpaved, and will deteriorate if maintenance remains inadequate. They are found mostly in the hinterland and riverain areas and provide linkages with a number of important mining and forestry activities thus facilitating transportation between the mining and forestry communities and the more developed coastal areas. Parts of this road/trail network can be developed into an arterial road system linking the hinterland communities with each other and to the main road network. It is estimated that roads carry 80 percent of Guyana's passenger traffic and about 33 percent of its freight.

Commuters to West Demerara have a choice of road transport via the Demerara Harbour Bridge or by the Demerara River ferry from the Stabroek Stelling to Vreed en Hoop, which is obliquely opposite. The highway that begins on the West Coast of Demerara is heavily trafficked since it provides a link to Parika on the East Bank of the Essequibo River, which has become an important center of economic activity in the Essequibo region.

It is now possible to travel overland to Suriname by taking the ferry on the Guyana side at Moleson Creek and crossing the Corentyne River over to Suriname at South Drain. While travel to Brazil is via the old cattle trail it has been upgraded into a fair weather track that passes through the bauxite-producing town of Linden and ending at Lethem.

Bridges
The coastal main road system is not continuous. There are gaps whenever it intersects the Essequibo, Demerara and Berbice Rivers. People and goods move across these gaps by ferry systems as well as the Demerara Harbour Bridge (DHB) and the Berbice Bridge.

The Demerara Harbour Bridge is a two-lane floating toll bridge, 1.2 mi long, near the mouth of the Demerara River. It is primarily a low-level bridge which possesses an elevated span with a vertical clearance of 26 ft in the middle of the river to permit small craft to pass. In addition, across the shipping channel, there are two spans which retract to permit the passage of ocean-going vessels. From mid-1998 toll revenue has been credited to the account of the DHB and not to the Government of Guyana, as it was until then. This is a step towards the establishment of the DHB as an autonomous statutory authority. At present the toll revenue does not meet the operational and maintenance costs of the bridge; the government of Guyana provides considerable subsidy for its upkeep. The bridge has been in existence since 1978 and currently notwithstanding the rigorous maintenance regime, sits at the end of its useful life.

In 2007, construction resumed on the Takutu River Bridge to link Guyana and Brazil in the southwest region of Guyana near Lethem. The bridge was officially opened on September 14, 2009, enabling economic interests in northern Brazil to link by road to the port at Georgetown. Unprecedented construction and population growth in Lethem since the bridge's opening reflects the significantly increased traffic and movement of goods facilitated by the bridge. The Takutu Bridge is seen as the first of several joint projects between Guyana and Brazil intended to facilitate cargo traffic: Brazil is expected to subsidize the paving of the Lethem-to-Georgetown road, a development that would have profound impacts on the area's economy and environment. Dredging of the Georgetown port to accommodate deeper-draft cargo vessels is also being planned.

Rail transport
Commercial railway services for both passengers and cargo were operated until 1974. Two lines operated - the Demerara-Essequibo Railway, from Vreed en Hoop to Parika (18.5 mi) and the Demerara-Berbice Railway, from Georgetown to Rosignol (65 mi). With the upgrading of the West Coast Demerara/East Bank Essequibo and the East Coast Demerara/West Coast Berbice roadways, the Government decided in the mid-1970s to cease operating the railway services, which were being run at a loss. In the Matthew's Ridge area, there is a 32 mi railway service.

A railway service was once operated in Linden for the movement of bauxite ore. However trucks are now used to transport the bauxite ore.

Water transport
It is generally agreed that, for the movement of bulky low-value goods over great distances, water transport is cheapest. This is especially true in Guyana, where the road infrastructure is poorly advanced. Moreover, with the widespread decentralization of economic activity that is being proposed by the government, and with the corresponding development of the interior regions of the country, the demand for water transport might, perhaps paradoxically, increase rather than diminish.

The infrastructure that supports water transport in Guyana is located along the banks of the navigable rivers, namely, the Essequibo River, Demerara River and Berbice River. In addition to the wharves and stellings that provide coastal and inland linkages, there are facilities that handle both the country's overseas and local shipping requirements.

Virtually all exports and imports are transported by sea. The main port of Georgetown, located at the mouth of the Demerara River, comprises several wharves, most of which are privately owned. In addition, three berths are available for oceangoing vessels at Linden.

Draught constraints limit the size of vessels using Georgetown's harbour to. However, recent improvements in the channel in the Berbice River have made it possible for ships of up to to dock there.

Guyana's foreign trade is handled by foreign shipping companies. The largest bulk exports are bauxite and sugar, and the largest volume imports are petroleum and wheat flour. Other important break-bulk exports include rice and timber.

Containers are used but because they are not part of the internal transport system, they are loaded and unloaded at the ports.

Internal barge transport is important for bauxite, sugar, rice and aggregates. In the case of sugar, for example, 98 percent of exports is delivered by barge to the port of Georgetown for export. Rivers are used for moving logs and account also for a significant share of those persons who travel to the interior.

It is estimated that about 1,000 kilometers of waterways in Guyana are utilized for commerce in Guyana. In addition, drainage canals are important transport channels for collecting sugar on the estates and for personal travel.

Ferries
Ferry services link the primary roads in the coastal area, and Guyana with Suriname. The Government's Transport an hid Harbour Department provides scheduled ferry services in the Essequibo and Demerara rivers. Small privately owned river-craft supplement these services. Since the opening of the Berbice River Bridge in December 2008 the Transport and Harbour Department has reduced its service to only one round trip daily between Rosignol and New Amsterdam.

Currently the only ferry service consistently showing profit is The Parika-Adventure. Service for the remainder, in particular The North West services, the Government provides a cross-subsidy funded out of the profits that are always realized by the Harbor Branch of the Transport and Harbors Department. Nevertheless, ferry operations have the potential to be profitable, provided that capital investments are made to improve their physical assets. With the establishment of a Maritime Administration and subsequently a National Sea Ports Authority the ferry operations may be privatized or operated as a commercially viable autonomous agency.

There is also a ferry linking Guyana and Suriname crossing the Corentyne River from Springlands (at Corriverton in Guyana) to Nieuw Nickerie, a town in Suriname. Leaving Rosignol at 8:00hrs and now at 14:30hrs respectively. This service is primarily geared at offsetting the high cost for crossing the Berbice Bridge for school children, public servants and the elderly.

Ultimately, key ferry links were to be replaced with bridges, starting with one from Rosignol to New Amsterdam across the Berbice River.

At the end of 1999 the fleet of ferry vessels owned by the Transport and Harbors Department comprised nine motor vessels, six of which ranged in age from 15 to 55 years. Indeed, two of the vessels were over fifty years of age, and three over 30 years, with an average age of thirty-five. They are in almost continuous need of repair.

Air transportation
Air transportation for business and pleasure is readily available for traveling to many parts of the hinterland. Several local airlines depart from both Ogle Airport on the East Coast Demerara, 6 mi south-east of Georgetown and from Cheddi Jagan International Airport, at Timehri, 25 mi south-west of Georgetown.

Air transport plays a vital role in the development of Guyana. Within the country, it provides a link between the coastal areas and communities in the hinterland, many of which are inaccessible by any other means of transportation. Thus, the economic and social well being of these areas and their integration into the fabric of the nation are critically dependent on the availability of air transport. Externally, passengers are moved to and from the country almost entirely by air. In addition, the potential of this mode of transport for the carriage of cargo, especially exports, continues to increase.

The first airplane flight took place in Guyana in March 1913 when George Schmidt, a German, flew a machine over Georgetown, taking off from the Bel Air Park Race Course.

In September 1929, the first airmail service to Guyana began.

The famous American flier, Colonel Charles Lindbergh, arrived in the Demerara River with his flying boat (an amphibian craft) on September 22, 1929. The first regular flights to the interior started in 1939.

Although air transport in Guyana had its beginnings in the 1920s when the first "bush" services were introduced, Government's earnest participation can be dated from 1947 when a Director of Civil Aviation was appointed to regulate the industry. Regular shipments of beef from the Rupununi to Georgetown by air began on 9 July 1948. Amphibian aircraft have been vital to the development of the country as they are able land both on airstrips and on water.

The development of air transport in Guyana owes much to Arthur "Art" James Williams, a pilot and mechanic from the United States. He arrived in British Guiana in August 1934, and returned to the United States in October 1955. Over this period, except for the war years, during which he served with the United States Air Force, he developed British Guiana Airways Ltd. (registered 27 May 1938) and operating regular internal services since 1939.

On 15 July 1955, the Government purchased British Guiana Airways. However, external services continued to be supplied almost exclusively by foreign airlines until Guyana Airways Corporation commenced regional air services in 1979. Subsequently, restrictions on the repatriation of profits in foreign exchange and other circumstances contributed to the withdrawal of services to Guyana by foreign airlines, with the exception of BWIA. Guyana Airways Corporation was therefore obliged to fill the breach by commencing jet operations to Miami and New York in the US and Toronto, Ontario in Canada.

In the 1980s Guyana Airways Corporation's domestic operations started to deteriorate for a number of reasons, not least among them the unrealistically low fares it was required to charge and the lack of access to foreign exchange for imported aircraft parts and other requirements. The private sector therefore began to fill the gap and by 1991 three major domestic charter operators had emerged. In the meantime, Guyana Airways Corporation's domestic service continued to deteriorate and, by 1993, possessed only one Twin Otter DHC-6 to service the entire country. Under new management it was revitalized and saw a partial return to its original domestic role with the reintroduction of several domestic scheduled routes, because of the addition of two Shorts Skyvan SC7 aircraft, and a second Twin Otter DHC-6 aircraft.

In 2010, the International Civil Aviation Organization (ICAO) conferred "international" status to the air terminal at Ogle (IATA: OGL, ICAO: SYGO), a former sugarcane airstrip just a few kilometres south of Georgetown's center. In anticipation of increased regional air traffic to the facility, an EU-subsidized construction project began in January of that year, intended to upgrade the terminal building and extend the primary paved runway to a usable length of 4000 feet. Ogle is the hub for domestic flights to Guyana's interior and offers once-daily service to the in-town airstrip in Paramaribo, capital of neighboring Suriname.

Challenges and future development
The gross inadequacy of Guyana's transportation system militates against its social and economic development in several ways. First, it increases production costs and, therefore, reduces competitiveness, particularly in the mining and forestry sectors. Second, it inhibits the capacity to fully utilise those natural resources (gold, timber, diamonds, soils suitable for agriculture) that are not located on the coastland. Third, by severely limiting communication between those who live on the coast and those who inhabit the hinterland, it effectively divides the country into two almost unbridgeable cultures. Fourth, it acts as a barrier to the unity of the country in both a physical and spiritual sense: because they are not unified physically, Guyanese seem to find it difficult to think as Guyanese, to act as if they are one nation. Fifth, it restricts the coastal population's penetration of the interior, and forces coastlanders to live in a cramped and crowded manner on the coast, struggling and competing for land-space and other amenities, while more suitable areas are available farther south. And sixth, failure to occupy the greater part of the country, might tend to bolster some of the claims of Guyana's neighbours to its territory.

The government of Guyana and Brazil signed a Memorandum of Understanding in 2012 to explore the development of Hydro Power, Linden-Lethem Road and Deep Water Harbour to boost bilateral trade and cooperation. This network would have enabled easy access by road to the neighbouring countries of Brazil, Venezuela and Surinam; reduced the costs of utilising the country's timber and natural resources, thus making them more competitive in international markets; diversified agricultural development by making more easily available suitable areas in the hinterland, particularly in the Intermediate and Rupununi savannahs; relieved the over-crowded coastland of a significant proportion of its population, thus improving the quality of life of the inhabitants of both the coastal and interior areas; and made more feasible the equitable distribution of economic activity, not only in the agricultural but also in the manufacturing and small- industries sector.

A high-span fixed bridge is currently being studied to replace the existing DHB; a series of bridges and causeways linking the islands in the mouth of the Essequibo River to Morasi on the East Bank and Supenaam on the West Bank; and another high-span bridge across the Essequibo River at Monkey Jump.

Construction of a bridge across the Berbice River at Crab Island and D'Edwards on the East and West banks of Berbice River was completed in 2008.

In 2012, The Government of Guyana signed a contract with CHEC of China for the expansion of the runway at the CJIA and the construction of a modern terminal building at an estimated cost of 131Million US Dollars. Moreover, the airstrip at Timehri Airport would have been extended, and the entire Airport refurbished to accommodate an increasing number of passengers. The airport at Ogle would have been privatised, and much improved and extended.

Railways
Total: 187 km (all dedicated to ore transport)

Standard gauge: 139 km;

Narrow gauge: 48 km; gauge

Highways
Total: 7,970 km

Paved: 590 km

Unpaved: 7,380 km (1996 est.)
 * Driving is on the left, a practice inherited from United Kingdom colonial authorities. Guyana and Suriname are the only two countries on the (in-land) American continent who still drive on the left.

Waterways
Guyana has 5900 km total of navigable waterways; Berbice River, Demerara River, and Essequibo River are navigable by oceangoing vessels for 150, respectively.

Seaports and harbors

 * Bartica
 * Georgetown
 * Linden
 * New Amsterdam
 * Parika

Merchant marine
total: 1 ship ( or over) totaling /

ships by type: (1999 est.)
 * cargo ship 1

Airports
51 (1999 est.)

International Airport: Cheddi Jagan International Airport

Other Major Airport/s: Eugene F. Correia International Airport

Airports - with paved runways:

total: 9

1,524 to 2,437 m: 2

914 to 1,523 m: 1

under 914 m: 2 (1999 est.)

Airports - with unpaved runways:

total: 84

1,524 to 2,437 m: 2

914 to 1,523 m: 7

under 914 m: 37 (1999 est.)

title: Transport in Guyana


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Foreign relations of Guyana

After independence in 1966, Guyana sought an influential role in international affairs, particularly among Third World and non-aligned nations. It served twice on the UN Security Council (1975–76 and 1982–83). Former Vice President, Deputy Prime Minister, and Attorney General Mohamed Shahabuddeen served a 9-year term on the International Court of Justice (1987–96). In June 2023, Guyana was elected as a non-permanent member to the UN Security Council. The country will serve on the Council for a period of two years, beginning in January 2024.

Guyana has diplomatic relations with a wide range of nations, and these are managed primarily through its Ministry of Foreign Affairs. The European Union (EU), the Inter-American Development Bank (IDB), the UN Development Programme (UNDP), the World Health Organization (WHO), and the Organization of American States (OAS) have offices in Georgetown.

Regional relations
Guyana strongly supports the concept of regional integration. It played an important role in the founding of the Caribbean Community and Common Market (CARICOM), but its historic status as the organization's poorest member limited its ability to exert leadership in regional activities. Since discovering and developing its offshore oil and gas reserves, Guyana has been reclassified by the World Bank as a high-income country. Guyana has sought to keep foreign policy in close alignment with the consensus of CARICOM members, especially in voting in the UN, OAS, and other international organizations. In 2022, Guyana joined the Regional Security System. The 2023 Guyana–Venezuela crisis has compelled Guyana to expand defense and security relations with a variety of countries, namely Brazil, the United States, India, and the United Kingdom.

International disputes
All of the area west of the Essequibo River has at one point been under dispute, namely by Venezuela and Brazil. In 1899, the government in Caracas reluctantly accepted the Venezuelan-Guyanese border but later revived its claim to the Essequibo in 1962. Suriname has an ongoing dispute with Guyana and this pertains to the area east of the Upper Courantyne.

Currently, two neighbours have longstanding territorial disputes with Guyana. Since the 19th century, Venezuela has claimed the majority or all of Guyana situated west of the Essequibo River – 62% of Guyana's territory. At a meeting in Geneva in 1966, the two countries agreed to receive recommendations from a representative of the UN Secretary General on ways to settle the dispute peacefully. Diplomatic contacts between the two countries and the Secretary General's representative continue. In December 2023 president Nicolás Maduro called for a public referendum which resulted in the government of Venezuela officially claiming ownership of the Essequibo, claim that resulted in the 2023 Guyana–Venezuela crisis.

Neighbouring Suriname also claims the territory east of Guyana's New River, a largely uninhabited area of some 15000 km2 in southeast Guyana. Guyana and Suriname also disputed their offshore maritime boundaries. This dispute flared up in June 2000 in response to an effort by a Canadian company to drill for oil under a Guyanese concession. Guyana regards its legal title to all of its territory as sound. However, the dispute with Suriname was arbitrated by the United Nations Convention on Law of the Sea and a ruling in favor of Guyana was announced in September 2007.

Crime
In 1993, Guyana ratified the 1988 Vienna Convention on illicit traffic in narcotic drugs and cooperates with US law enforcement agencies on counter-narcotics efforts. Guyana is also a member of the International Criminal Court with a Bilateral Immunity Agreement of protection for the US-military (as covered under Article 98).

Guyana has been considered a transshipment point for narcotics from South America, primarily Venezuela, to Europe and the United States and producer of cannabis.

Relations by country
List of countries which Guyana has diplomatic relations with:

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Foreign relations of Guyana


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Geology

Geology  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 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 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 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.

Geological material
The majority of geological data comes from research on solid Earth materials. Meteorites and other extraterrestrial natural materials are also studied by geological methods.

Mineral
Minerals are naturally occurring elements and compounds with 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:
 * Color: Minerals are grouped by their color. Mostly diagnostic but impurities can change a mineral's color.
 * Streak: Performed by scratching the sample on a porcelain plate. The color of the streak can help identify the mineral.
 * Hardness: The resistance of a mineral to scratching or indentation.
 * Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces, and the latter a breakage along closely spaced parallel planes.
 * Luster: Quality of light reflected from the surface of a mineral. Examples are metallic, pearly, waxy, dull.
 * Specific gravity: the weight of a specific volume of a mineral.
 * Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing.
 * Magnetism: Involves using a magnet to test for magnetism.
 * Taste: Minerals can have a distinctive taste such as halite (which tastes like table salt).

Rock

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 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 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 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.

Unlithified material
Geologists also study unlithified materials (referred to as superficial deposits) that lie above 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
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.

Plate tectonics

In 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 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 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:

 * Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart.
 * Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another.
 * Transform boundaries, such as the San Andreas Fault system, are where plates slide horizontally past each other.

Plate tectonics has provided a mechanism for Alfred Wegener's theory of continental drift, in which the continents move across 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.

Earth structure

Advances in seismology, computer modeling, and mineralogy and crystallography at high temperatures and pressures give insights into 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, 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 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 the mantle and show the crystallographic structures expected in the inner core of the Earth.

Geological time
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 the later end of the scale, it is marked by the present day (in the Holocene epoch).

Important milestones on Earth

 * 4.567 Ga (gigaannum: billion years ago): Solar system formation
 * 4.54 Ga: Accretion, or formation, of Earth
 * c. 4 Ga: End of Late Heavy Bombardment, the first life
 * c. 3.5 Ga: Start of photosynthesis
 * c. 2.3 Ga: Oxygenated atmosphere, first snowball Earth
 * 730–635 Ma (megaannum: million years ago): second snowball Earth
 * 541 ± 0.3 Ma: Cambrian explosion – vast multiplication of hard-bodied life; first abundant fossils; start of the Paleozoic
 * c. 380 Ma: First vertebrate land animals
 * 250 Ma: Permian-Triassic extinction – 90% of all land animals die; end of Paleozoic and beginning of Mesozoic
 * 66 Ma: Cretaceous–Paleogene extinction – Dinosaurs die; end of Mesozoic and beginning of Cenozoic
 * c. 7 Ma: First hominins appear
 * 3.9 Ma: First Australopithecus, direct ancestor to modern Homo sapiens, appear
 * 200 ka (kiloannum: thousand years ago): First modern Homo sapiens appear in East Africa

Relative dating

Methods for relative dating were developed when geology first emerged as a natural science. Geologists still use the following principles today as 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 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 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 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 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 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 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, 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.

Absolute dating

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 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 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 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 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 is used for geologically young materials containing organic carbon.

Geological development of an area

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 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 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 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 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 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 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 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 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 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 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 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, 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.

Investigative methods

Geologists use 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 the subsurface. Sub-specialities of geology may distinguish endogenous and exogenous geology.

Field methods

Geological field work varies depending on the task at hand. Typical fieldwork could consist of:
 * Geological mapping
 * Structural mapping: identifying the locations of major rock units and the faults and folds that led to their placement there.
 * Stratigraphic mapping: pinpointing the locations of sedimentary facies (lithofacies and biofacies) or the mapping of isopachs of equal thickness of sedimentary rock
 * Surficial mapping: recording the locations of soils and surficial deposits
 * Surveying of topographic features
 * compilation of topographic maps
 * Work to understand change across landscapes, including:
 * Patterns of erosion and deposition
 * River-channel change through migration and avulsion
 * Hillslope processes
 * Subsurface mapping through geophysical methods
 * These methods include:
 * Shallow seismic surveys
 * Ground-penetrating radar
 * Aeromagnetic surveys
 * Electrical resistivity tomography
 * They aid in:
 * Hydrocarbon exploration
 * Finding groundwater
 * Locating buried archaeological artifacts
 * High-resolution stratigraphy
 * Measuring and describing stratigraphic sections on the surface
 * Well drilling and logging
 * Biogeochemistry and geomicrobiology
 * Collecting samples to:
 * determine biochemical pathways
 * identify new species of organisms
 * identify new chemical compounds
 * and to use these discoveries to:
 * understand early life on Earth and how it functioned and metabolized
 * find important compounds for use in pharmaceuticals
 * Paleontology: excavation of fossil material
 * For research into past life and evolution
 * For museums and education
 * Collection of samples for geochronology and thermochronology
 * Glaciology: measurement of characteristics of glaciers and their motion

Petrology
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 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 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 the Earth, such as subduction and magma chamber evolution.

Structural geology

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 the history of rock deformation in the area. In addition, they perform analog and numerical experiments of rock deformation in large and small settings.

The analysis of structures is often accomplished by plotting the orientations of various features onto stereonets. A stereonet is a stereographic projection of a sphere onto a plane, in which planes are projected as lines and lines are projected as points. These can be used to find the locations of fold axes, relationships between faults, and relationships between other geological structures.

Among the most well-known experiments in structural geology are those involving orogenic wedges, which are zones in which mountains are built along convergent tectonic plate boundaries. In the analog versions of these experiments, horizontal layers of sand are pulled along a lower surface into a back stop, which results in realistic-looking patterns of faulting and the growth of a critically tapered (all angles remain the same) orogenic wedge. Numerical models work in the same way as these analog models, though they are often more sophisticated and can include patterns of erosion and uplift in the mountain belt. This helps to show the relationship between erosion and the shape of a mountain range. These studies can also give useful information about pathways for metamorphism through pressure, temperature, space, and time.

Stratigraphy

In the laboratory, stratigraphers analyze samples of stratigraphic sections that can be returned from the field, such as those from drill cores. Stratigraphers also analyze data from geophysical surveys that show the locations of stratigraphic units in the subsurface. Geophysical data and well logs can be combined to produce a better view of the subsurface, and stratigraphers often use computer programs to do this in three dimensions. Stratigraphers can then use these data to reconstruct ancient processes occurring on the surface of the Earth, interpret past environments, and locate areas for water, coal, and hydrocarbon extraction.

In the laboratory, biostratigraphers analyze rock samples from outcrop and drill cores for the fossils found in them. These fossils help scientists to date the core and to understand the depositional environment in which the rock units formed. Geochronologists precisely date rocks within the stratigraphic section to provide better absolute bounds on the timing and rates of deposition. Magnetic stratigraphers look for signs of magnetic reversals in igneous rock units within the drill cores. Other scientists perform stable-isotope studies on the rocks to gain information about past climate.

Planetary geology

With the advent of space exploration in the twentieth century, geologists have begun to look at other planetary bodies in the same ways that have been developed to study the Earth. This new field of study is called planetary geology (sometimes known as astrogeology) and relies on known geological principles to study other bodies of the solar system. This is a major aspect of planetary science, and largely focuses on the terrestrial planets, icy moons, asteroids, comets, and meteorites. However, some planetary geophysicists study the giant planets and exoplanets.

Although the Greek-language-origin prefix geo refers to Earth, "geology" is often used in conjunction with the names of other planetary bodies when describing their composition and internal processes: examples are "the geology of Mars" and "Lunar geology". Specialized terms such as selenology (studies of the Moon), areology (of Mars), etc., are also in use.

Although planetary geologists are interested in studying all aspects of other planets, a significant focus is to search for evidence of past or present life on other worlds. This has led to many missions whose primary or ancillary purpose is to examine planetary bodies for evidence of life. One of these is the Phoenix lander, which analyzed Martian polar soil for water, chemical, and mineralogical constituents related to biological processes.

Economic geology
Economic geology is a branch of geology that deals with aspects of economic minerals that humankind uses to fulfill various needs. Economic minerals are those extracted profitably for various practical uses. Economic geologists help locate and manage the Earth's natural resources, such as petroleum and coal, as well as mineral resources, which include metals such as iron, copper, and uranium.

Mining geology
Mining geology consists of the extractions of mineral and ore resources from the Earth. Some resources of economic interests include gemstones, metals such as gold and copper, and many minerals such as asbestos, Magnesite, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium.

Petroleum geology

Petroleum geologists study the locations of the subsurface of the Earth that can contain extractable hydrocarbons, especially petroleum and natural gas. Because many of these reservoirs are found in sedimentary basins, they study the formation of these basins, as well as their sedimentary and tectonic evolution and the present-day positions of the rock units.

Engineering geology
Engineering geology is the application of geological principles to engineering practice for the purpose of assuring that the geological factors affecting the location, design, construction, operation, and maintenance of engineering works are properly addressed. Engineering geology is distinct from geological engineering, particularly in North America.

In the field of civil engineering, geological principles and analyses are used in order to ascertain the mechanical principles of the material on which structures are built. This allows tunnels to be built without collapsing, bridges and skyscrapers to be built with sturdy foundations, and buildings to be built that will not settle in clay and mud.

Hydrology
Geology and geological principles can be applied to various environmental problems such as stream restoration, the restoration of brownfields, and the understanding of the interaction between natural habitat and the geological environment. Groundwater hydrology, or hydrogeology, is used to locate groundwater, which can often provide a ready supply of uncontaminated water and is especially important in arid regions, and to monitor the spread of contaminants in groundwater wells.

Paleoclimatology
Geologists also obtain data through stratigraphy, boreholes, core samples, and ice cores. Ice cores and sediment cores are used for paleoclimate reconstructions, which tell geologists about past and present temperature, precipitation, and sea level across the globe. These datasets are our primary source of information on global climate change outside of instrumental data.

Natural hazards

Geologists and geophysicists study natural hazards in order to enact safe building codes and warning systems that are used to prevent loss of property and life. Examples of important natural hazards that are pertinent to geology (as opposed those that are mainly or only pertinent to meteorology) are: • Avalanches

• Earthquakes

• Floods

• Landslides and debris flows

• River channel migration and avulsion

• Rockfalls

• Sinkholes

• Soil liquefaction

• Subsidence

• Tsunamis

• Volcanoes

History
The study of the physical material of the Earth dates back at least to ancient Greece when Theophrastus (372–287 BCE) wrote the work Peri Lithon (On Stones). During the Roman period, Pliny the Elder wrote in detail of the many minerals and metals, then in practical use – even correctly noting the origin of amber. Additionally, in the 4th century BCE Aristotle made critical observations of the slow rate of geological change. He observed the composition of the land and formulated a theory where the Earth changes at a slow rate and that these changes cannot be observed during one person's lifetime. Aristotle developed one of the first evidence-based concepts connected to the geological realm regarding the rate at which the Earth physically changes.

Abu al-Rayhan al-Biruni (973–1048 CE) was one of the earliest Persian geologists, whose works included the earliest writings on the geology of India, hypothesizing that the Indian subcontinent was once a sea. Drawing from Greek and Indian scientific literature that were not destroyed by the Muslim conquests, the Persian scholar Ibn Sina (Avicenna, 981–1037) proposed detailed explanations for the formation of mountains, the origin of earthquakes, and other topics central to modern geology, which provided an essential foundation for the later development of the science. In China, the polymath Shen Kuo (1031–1095) formulated a hypothesis for the process of land formation: based on his observation of fossil animal shells in a geological stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by the erosion of the mountains and by deposition of silt.

Georgius Agricola (1494–1555) published his groundbreaking work De Natura Fossilium in 1546 and is seen as the founder of geology as a scientific discipline.

Nicolas Steno (1638–1686) is credited with the law of superposition, the principle of original horizontality, and the principle of lateral continuity: three defining principles of stratigraphy.

The word geology was first used by Ulisse Aldrovandi in 1603, then by Jean-André Deluc in 1778 Deluc, Jean André de, ''Lettres physiques et morales sur les montagnes et sur l'histoire de la terre et de l'homme. …'' [Physical and moral letters on mountains and on the history of the Earth and man. … ], vol. 1 (Paris, France: V. Duchesne, 1779), pp. 4, 5, and 7. From p. 4:  "Entrainé par les liaisons de cet objet avec la Géologie, j'entrepris dans un second voyage de les développer à SA MAJESTÉ; … " (Driven by the connections between this subject and geology, I undertook a second voyage to develop them for Her Majesty [viz, Charlotte of Mecklenburg-Strelitz, Queen of Great Britain and Ireland]; … )  From p. 5:   "Je vis que je faisais un Traité, et non une equisse de Géologie."  (I see that I wrote a treatise, and not a sketch of geology.)  From the footnote on p. 7:   "Je répète ici, ce que j'avois dit dans ma première Préface, sur la substitution de mot Cosmologie à celui de Géologie, quoiqu'il ne s'agisse pas de l'Univers, mais seulement de la Terre: … "  (I repeat here what I said in my first preface about the substitution of the word "cosmology" for that of "geology", although it is not a matter of the universe but only of the Earth: … ) [Note:  A pirated edition of this book was published in 1778.] and introduced as a fixed term by Horace-Bénédict de Saussure in 1779. On the controversy regarding whether Deluc or Saussure deserves priority in the use the term "geology":
 * Zittel, Karl Alfred von, with Maria M. Ogilvie-Gordon, trans., History of Geology and Paleontology to the End of the Nineteenth Century (London, England: Walter Scott, 1901), p. 76.
 * Geikie, Archibald, The Founders of Geology, 2nd ed. (London, England: Macmillan and Co., 1905), p. 186.
 * Eastman, Charles Rochester (12 August 1904) Letter to the Editor: "Variæ Auctoritatis", Science, 2nd series, 20 (502) : 215–217 ; see p. 216.
 * Emmons, Samuel Franklin (21 October 1904) Letter to the Editor: "Variæ Auctoritatis", Science, 2nd series, 20 (512) :  537.
 * Eastman, C.R. (25 November 1904) Letter to the Editor: "Notes on the History of Scientific Nomenclature",  Science, 2nd series, 20 (517) :  727–730 ; see p. 728.
 * Emmons, S.F. (23 December 1904) Letter to the Editor: "The term 'geology' ", Science, 2nd series, 20 (521) :  886–887.
 * Eastman, C. R. (20 January 1905) Letter to the Editor: "Deluc's 'Geological Letters'", Science, 2nd series, 21 (525):  111.
 * Emmons, S. F. (17 February 1905) Letter to the Editor: "Deluc versus de Saussure", Science, 2nd series, 21 (529) :  274–275. The word is derived from the Greek γῆ, gê, meaning "earth" and λόγος, logos, meaning "speech". But according to another source, the word "geology" comes from a Norwegian, Mikkel Pedersøn Escholt (1600–1669), who was a priest and scholar. Escholt first used the definition in his book titled, Geologia Norvegica (1657).

William Smith (1769–1839) drew some of the first geological maps and began the process of ordering rock strata (layers) by examining the fossils contained in them.

In 1763, Mikhail Lomonosov published his treatise On the Strata of Earth. His work was the first narrative of modern geology, based on the unity of processes in time and explanation of the Earth's past from the present.

James Hutton (1726–1797) is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Hutton published a two-volume version of his ideas in 1795.

Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism, which is the deposition of lava from volcanoes, as opposed to the Neptunists, led by Abraham Werner, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time.

The first geological map of the U.S. was produced in 1809 by William Maclure. In 1807, Maclure commenced the self-imposed task of making a geological survey of the United States. Almost every state in the Union was traversed and mapped by him, the Allegheny Mountains being crossed and recrossed some 50 times. The results of his unaided labours were submitted to the American Philosophical Society in a memoir entitled Observations on the Geology of the United States explanatory of a Geological Map, and published in the Society's Transactions, together with the nation's first geological map. This antedates William Smith's geological map of England by six years, although it was constructed using a different classification of rocks.

Sir Charles Lyell (1797–1875) first published his famous book, Principles of Geology, in 1830. This book, which influenced the thought of Charles Darwin, successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time.

Much of 19th-century geology revolved around the question of the Earth's exact age. Estimates varied from a few hundred thousand to billions of years. By the early 20th century, radiometric dating allowed the Earth's age to be estimated at two billion years. The awareness of this vast amount of time opened the door to new theories about the processes that shaped the planet.

Some of the most significant advances in 20th-century geology have been the development of the theory of plate tectonics in the 1960s and the refinement of estimates of the planet's age. Plate tectonics theory arose from two separate geological observations: seafloor spreading and continental drift. The theory revolutionized the Earth sciences. Today the Earth is known to be approximately 4.5 billion years old.

Fields or related disciplines

 * Earth system science
 * Economic geology
 * Mining geology
 * Petroleum geology
 * Engineering geology
 * Environmental geology
 * Environmental science
 * Geoarchaeology
 * Geochemistry
 * Biogeochemistry
 * Isotope geochemistry
 * Geochronology
 * Geodetics
 * Geography
 * Physical geography
 * Technical geography
 * Geological engineering
 * Geological modelling
 * Geometallurgy
 * Geomicrobiology
 * Geomorphology
 * Geomythology
 * Geophysics
 * Glaciology
 * Historical geology
 * Hydrogeology
 * Meteorology
 * Mineralogy
 * Oceanography
 * Marine geology
 * Paleoclimatology
 * Paleontology
 * Micropaleontology
 * Palynology
 * Petrology
 * Petrophysics
 * Planetary geology
 * Plate tectonics
 * Regional geology
 * Sedimentology
 * Seismology
 * Soil science
 * Pedology (soil study)
 * Speleology
 * Stratigraphy
 * Biostratigraphy
 * Chronostratigraphy
 * Lithostratigraphy
 * Structural geology
 * Systems geology
 * Tectonics
 * Volcanology

title: Geology


text:
User:Geoboy

Welcome, Geoboy!

I hope you have fun colaborating in this enterprise.--AstroNomer

title: User:Geoboy