Portal:Geology
The Geology Portal
Geology (from Ancient Greek γῆ (gê) 'earth' and λoγία (-logía) 'study of, discourse') 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. (Full article...)
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Map of SSSIs in Cornwall within the UK
There are 167 Sites of Special Scientific Interest (SSSIs) in Cornwall (including the Isles of Scilly). Cornwall, in the south-west of England, UK, has a population of 575,413 (2022) across an area of 3,545 km2 (875,988.6 acres), making it one of the least densely populated counties within England. The north coast of Cornwall falls on the Celtic Sea in the Atlantic Ocean, which also surrounds the Isles of Scilly, the south coast falls on the English Channel and the county is bounded by the River Tamar, forming the border with Devon, to the east. Cornish geology consists mainly of rocks from the Devonian and Carboniferous geological periods. Granite forms a large part of these, with mineralisations of tin, copper, lead and arsenic having been mined in the area. This gives rise to many distinct habitats, with strong marine influences, including sand dunes, rocky reefs, stacks and headlands as well as heathland, moorland and unusual river profiles.
In England the body responsible for designating SSSIs is Natural England, which chooses a site "because of its flora, fauna, or geological or physiographical features". Natural England took over the role of designating and managing SSSIs from English Nature in October 2006 when it was formed from the amalgamation of English Nature, parts of the Countryside Agency and the Rural Development Service. Natural England, like its predecessor, uses the 1974–96 county system and as such the same approach is followed here, rather than adopting the current local government or ceremonial county boundaries. (Full article...) -
A map of Resolution Guyot's bathymetric relief
Resolution Guyot (formerly known as Huevo) is a guyot (tablemount) in the underwater Mid-Pacific Mountains in the Pacific Ocean. It is a circular flat mountain, rising 500 metres (1,600 ft) above the seafloor to a depth of about 1,320 metres (4,330 ft), with a 35-kilometre-wide (22-mile) summit platform. The Mid-Pacific Mountains lie west of Hawaii and northeast of the Marshall Islands, but at the time of its formation, the guyot was located in the Southern Hemisphere.
The guyot was probably formed by a hotspot in today's French Polynesia before plate tectonics shifted it to its present-day location. The Easter, Marquesas, Pitcairn and Society hotspots, among others, may have been involved in the formation of Resolution Guyot. Volcanic activity has been dated to have occurred 107–129 million years ago and formed a volcanic island that was subsequently flattened by erosion. Carbonate deposition commenced, forming an atoll-like structure and a carbonate platform. (Full article...) -
Changes in surface air temperature over the past 50 years. The Arctic has warmed the most, and temperatures on land have generally increased more than sea surface temperatures.
Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The current rise in global temperatures is driven by human activities, especially fossil fuel burning since the Industrial Revolution. Fossil fuel use, deforestation, and some agricultural and industrial practices release greenhouse gases. These gases absorb some of the heat that the Earth radiates after it warms from sunlight, warming the lower atmosphere. Carbon dioxide, the primary greenhouse gas driving global warming, has grown by about 50% and is at levels not seen for millions of years.
Climate change has an increasingly large impact on the environment. Deserts are expanding, while heat waves and wildfires are becoming more common. Amplified warming in the Arctic has contributed to thawing permafrost, retreat of glaciers and sea ice decline. Higher temperatures are also causing more intense storms, droughts, and other weather extremes. Rapid environmental change in mountains, coral reefs, and the Arctic is forcing many species to relocate or become extinct. Even if efforts to minimize future warming are successful, some effects will continue for centuries. These include ocean heating, ocean acidification and sea level rise. (Full article...) -
The Mount Edziza volcanic complex (MEVC) in British Columbia, Canada, has a history of volcanism that spans more than 7 million years. It has taken place during five cycles of magmatic activity, each producing less volcanic material than the previous one. Volcanism during these cycles has created several types of volcanoes, including cinder cones, stratovolcanoes, subglacial volcanoes, shield volcanoes and lava domes. The roughly 1,000-square-kilometre (400-square-mile) volcanic plateau forming the base of the MEVC originated from the successive eruptions of highly mobile lava flows. Volcanic rocks such as basalt, trachybasalt, benmoreite, tristanite, mugearite, trachyte and rhyolite were deposited by multiple eruptions of the MEVC; the latter six rock types are products of varying degrees of magmatic differentiation in underground magma reservoirs. At least 10 distinct flows of obsidian were produced by volcanism of the MEVC, some of which were exploited by indigenous peoples in prehistoric times to make tools and weaponry. Renewed volcanism could produce explosive eruptions and block local streams with lava flows.
The first magmatic cycle took place between 7.5 and 6 million years ago and is represented by the Raspberry, Little Iskut and Armadillo geological formations, each of which is the product of a different eruptive period. Three distinct periods of eruptive activity also characterized the second magmatic cycle between 6 and 1 million years ago; they are represented by the Nido, Spectrum and Pyramid geological formations. The third magmatic cycle about 1 million years ago is represented by the Ice Peak, Pillow Ridge and Edziza geological formations, each of which is also the product of a distinct eruptive period. Three distinct periods of eruptive activity also characterized the fourth magmatic cycle between 0.8 and 0.2 million years ago which are represented by the Arctic Lake, Klastline and Kakiddi geological formations. The fifth magmatic cycle began at least 20,000 years ago and may be ongoing; the single distinct eruptive period of this magmatic cycle is represented by the Big Raven Formation. (Full article...) -
Bryce Canyon National Park (/braɪs/) is a national park of the United States located in southwestern Utah. The major feature of the park is Bryce Canyon, which despite its name, is not a canyon, but a collection of giant natural amphitheaters along the eastern side of the Paunsaugunt Plateau. Bryce is distinctive due to geological structures called hoodoos, formed by frost weathering and stream erosion of the river and lake bed sedimentary rock. The red, orange, and white colors of the rocks provide spectacular views for park visitors. Bryce Canyon National Park is much smaller and sits at a much higher elevation than nearby Zion National Park. The rim at Bryce varies from 8,000 to 9,000 feet (2,400 to 2,700 m).
The area is in portions of Garfield County and Kane County. (Full article...) -
The 2002 Bou'in-Zahra earthquake (also known as the 2002 Avaj earthquake or the 2002 Changureh earthquake) occurred on 22 June 2002. The epicenter was near the city of Bou'in-Zahra in Qazvin Province, a region of northwestern Iran which is crossed by several major faults that is known for destructive earthquakes. The shock measured 6.5 on the Mwc scale, had a maximum Mercalli intensity of VIII (Severe), and was followed by more than 20 aftershocks. At least 230 people were killed and 1,500 more were injured.
According to the International Institute of Earthquake Engineering and Seismology (IIEES), the earthquake was felt as far away as the capital city of Tehran, approximately 290 kilometres (180 mi) east of the epicenter, although no damage was reported there. Most houses in the region were single-story masonry buildings, and virtually all of these collapsed. The public became angry due to the slow official response to victims who needed supplies. Residents of the town of Avaj resorted to throwing stones at the car of a government minister. (Full article...) -
David Alexander Johnston (December 18, 1949 – May 18, 1980) was an American United States Geological Survey (USGS) volcanologist who was killed by the 1980 eruption of Mount St. Helens in the U.S. state of Washington. A principal scientist on the USGS monitoring team, Johnston was killed in the eruption while manning an observation post six miles (10 km) away on the morning of May 18, 1980. He was the first to report the eruption, transmitting "Vancouver! Vancouver! This is it!" before he was swept away by a lateral blast; despite a thorough search, Johnston's body was never found, but state highway workers discovered remnants of his USGS trailer in 1993.
Johnston's career took him across the United States, where he studied the Augustine Volcano in Alaska, the San Juan volcanic field in Colorado, and long-extinct volcanoes in Michigan. Johnston was a meticulous and talented scientist, known for his analyses of volcanic gases and their relationship to eruptions. This, along with his enthusiasm and positive attitude, made him liked and respected by many co-workers. After his death, other scientists lauded his character, both verbally and in dedications and letters. Johnston felt scientists must do what is necessary, including taking risks, to help protect the public from natural disasters. His work, and that of fellow USGS scientists, convinced authorities to close Mount St. Helens to the public before the 1980 eruption. They maintained the closure despite heavy pressure to re-open the area; their work saved thousands of lives. His story became intertwined with the popular image of volcanic eruptions and their threat to society, and a part of volcanology's history. To date, Johnston, along with his mentee Harry Glicken, is one of two American volcanologists known to have died in a volcanic eruption. (Full article...) -
The 1968 Illinois earthquake (a New Madrid event) was the largest recorded earthquake in the U.S. Midwestern state of Illinois. Striking at 11:02 a.m. on November 9, it measured 5.3 on the Richter scale. Although no fatalities occurred, the event caused considerable structural damage to buildings, including the toppling of chimneys and shaking in Chicago, the region's largest city. The earthquake was one of the most widely felt in U.S. history, largely affecting 23 states over an area of 580,000 sq mi (1,500,000 km2). In studying its cause, scientists discovered the Cottage Grove Fault in the Southern Illinois Basin.
Within the region, millions felt the rupture. Reactions to the earthquake varied; some people near the epicenter did not react to the shaking, while others panicked. A future earthquake in the region is extremely likely; in 2005, seismologists and geologists estimated a 90% chance of a magnitude 6–7 tremor before 2055, likely originating in the Wabash Valley seismic zone on the Illinois–Indiana border or the New Madrid fault zone. (Full article...) -
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kg (55 lb) also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the current era, the Cenozoic. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, Fatkito boundary or K–T boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium, which is more common in asteroids than in the Earth's crust.
As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter, it is now generally thought that the K–Pg extinction was caused by the impact of a massive asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago causing the Chicxulub crater, which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton. The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180 km (112 mi) Chicxulub crater in the Gulf of Mexico's Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid. A 2016 drilling project into the Chicxulub peak ring confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain. In October 2019, researchers asserted that the event rapidly acidified the oceans and produced long-lasting effects on the climate, detailing the mechanisms of the mass extinction. (Full article...) -
The ACFEL ice auger showing an ice core pushed up into the core remover barrel.
Ice drilling allows scientists studying glaciers and ice sheets to gain access to what is beneath the ice, to take measurements along the interior of the ice, and to retrieve samples. Instruments can be placed in the drilled holes to record temperature, pressure, speed, direction of movement, and for other scientific research, such as neutrino detection.
Many different methods have been used since 1840, when the first scientific ice drilling expedition attempted to drill through the Unteraargletscher in the Alps. Two early methods were percussion, in which the ice is fractured and pulverized, and rotary drilling, a method often used in mineral exploration for rock drilling. In the 1940s, thermal drills began to be used; these drills melt the ice by heating the drill. Drills that use jets of hot water or steam to bore through ice soon followed. A growing interest in ice cores, used for palaeoclimatological research, led to ice coring drills being developed in the 1950s and 1960s, and there are now many different coring drills in use. For obtaining ice cores from deep holes, most investigators use cable-suspended electromechanical drills, which use an armoured cable to carry electrical power to a mechanical drill at the bottom of the borehole. (Full article...)
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Vital articles to understand Geology.
The Chicxulub crater (IPA: [t͡ʃikʃuˈluɓ] cheek-shoo-LOOB) is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore, but the crater is named after the onshore community of Chicxulub Pueblo (not the larger coastal town of Chicxulub Puerto). It was formed slightly over 66 million years ago when an asteroid, about ten kilometers (six miles) in diameter, struck Earth. The crater is estimated to be 200 kilometers (120 miles) in diameter and 1 kilometer (0.62 miles) in depth. It is believed to be the second largest impact structure on Earth, and the only one whose peak ring is intact and directly accessible for scientific research. (Full article...)
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For editor resources and to collaborate with other editors on improving Wikipedia's Geology-related articles, visit WikiProject Geology.
Featured biography
Featured biography articles in Geology
Wolfgang "Wolf" Helmut Berger (5 October 1937, Erlangen – 6 August 2017 San Diego, California) was a German-American oceanographer, geologist, micropaleontologist and emeritus professor at Scripps Institution of Oceanography and the University of California, San Diego. His research interests comprise "micropaleontology, marine sedimentation, ocean productivity, carbon cycle, ocean history, climate history, and history of oceanography." (Full article...)
Did you know
Did you know it about Geology?
- ... that the Danish geologist Tove Birkelund received a gold medal for her early work on fossils of Scaphites in Greenland?
- ... that Karen Hanghøj, the 2023 winner of the William Smith Medal for applied geology, became the first female director of the British Geological Survey, 183 years after it was founded?
- ... that the groundwater level of a coastal aquifer system changes with the tide?
- ... that English amateur geologist Charlotte Eyton wrote a number of papers and pamphlets on the geology of the Wrekin, a part of Shropshire, between 1862 and 1870?
- ... that Frederick Murray Trotter had a distinguished career as a field geologist despite losing a part of his skull and an eye to shrapnel during World War I?
- ... that the Apollo 12 Solar Wind Spectrometer detected a gas-ion shockwave produced by the impact of the Apollo 13 S-IVB stage on the lunar surface?
- ... that from 1904 to 1911 Arthur Lewis Hall covered 17,479 miles (28,130 km), mostly on foot, to map the geology of the Transvaal?
- ... that the geology of the Ellsworth Mountains was explored by geologists using motor toboggans in 1961?
Top 10 WikiProject Geology Popular articles of the month
This following Geology-related articles is a most visited articles of WikiProject Geology, See complete list at Wikipedia:WikiProject Geology/Popular pages.
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Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere. Most of Earth's land is at least somewhat humid and covered by vegetation, while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation. (Full article...) -
Mount Everest, known locally as Sagarmatha or Qomolangma, is Earth's highest mountain above sea level, located in the Mahalangur Himal sub-range of the Himalayas. The China–Nepal border runs across its summit point. Its elevation (snow height) of 8,848.86 m (29,031 ft 8+1⁄2 in) was most recently established in 2020 by the Chinese and Nepali authorities. (Full article...) -
Animated, colour-coded map showing some continents and the region of Oceania (purple), which includes the continent of Australia. Depending on the convention and model, some continents may be consolidated or subdivided.
A continent is any of several large geographical regions. Continents are generally identified by convention rather than any strict criteria. A continent could be a single landmass or a part of a very large landmass, as in the case of Asia or Europe. Due to this, the number of continents varies; up to seven or as few as four geographical regions are commonly regarded as continents. Most English-speaking countries recognize seven regions as continents. In order from largest to smallest in area, these seven regions are Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Different variations with fewer continents merge some of these regions; examples of this are merging North America and South America into America, Asia and Europe into Eurasia, and Africa, Asia, and Europe into Afro-Eurasia. (Full article...) -
The Chicxulub crater (IPA: [t͡ʃikʃuˈluɓ] cheek-shoo-LOOB) is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore, but the crater is named after the onshore community of Chicxulub Pueblo (not the larger coastal town of Chicxulub Puerto). It was formed slightly over 66 million years ago when an asteroid, about ten kilometers (six miles) in diameter, struck Earth. The crater is estimated to be 200 kilometers (120 miles) in diameter and 1 kilometer (0.62 miles) in depth. It is believed to be the second largest impact structure on Earth, and the only one whose peak ring is intact and directly accessible for scientific research. (Full article...) -
Charles Robert Darwin (/ˈdɑːrwɪn/ DAR-win; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended from a common ancestor is now generally accepted and considered a fundamental scientific concept. In a joint publication with Alfred Russel Wallace, he introduced his scientific theory that this branching pattern of evolution resulted from a process he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding. Darwin has been described as one of the most influential figures in human history and was honoured by burial in Westminster Abbey. (Full article...) -
Changes in surface air temperature over the past 50 years. The Arctic has warmed the most, and temperatures on land have generally increased more than sea surface temperatures.
Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The current rise in global temperatures is driven by human activities, especially fossil fuel burning since the Industrial Revolution. Fossil fuel use, deforestation, and some agricultural and industrial practices release greenhouse gases. These gases absorb some of the heat that the Earth radiates after it warms from sunlight, warming the lower atmosphere. Carbon dioxide, the primary greenhouse gas driving global warming, has grown by about 50% and is at levels not seen for millions of years. (Full article...) -
Gold is a chemical element with the chemical symbol Au (from Latin aurum) and atomic number 79. In its pure form, it is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal, a group 11 element, and one of the noble metals. It is one of the least reactive chemical elements, being the second-lowest in the reactivity series. It is solid under standard conditions. (Full article...)
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Location of the Mariana Trench
The Mariana Trench is an oceanic trench located in the western Pacific Ocean, about 200 kilometres (124 mi) east of the Mariana Islands; it is the deepest oceanic trench on Earth. It is crescent-shaped and measures about 2,550 km (1,580 mi) in length and 69 km (43 mi) in width. The maximum known depth is 10,984 ± 25 metres (36,037 ± 82 ft; 6,006 ± 14 fathoms; 6.825 ± 0.016 mi) at the southern end of a small slot-shaped valley in its floor known as the Challenger Deep. The deepest point of the trench is more than 2 km (1.2 mi) farther from sea level than the peak of Mount Everest. (Full article...) -
Asbestos (/æsˈbɛstəs, æz-, -tɒs/ ass-BES-təs, az-, -toss) is a group of naturally occurring, toxic, carcinogenic and fibrous silicate minerals. There are six types, all of which are composed of long and thin fibrous crystals, each fibre (particulate with length substantially greater than width) being composed of many microscopic "fibrils" that can be released into the atmosphere by abrasion and other processes. Inhalation of asbestos fibres can lead to various dangerous lung conditions, including mesothelioma, asbestosis, and lung cancer. As a result of these health effects, asbestos is considered a serious health and safety hazard. (Full article...) -
The 2004 Indian Ocean tsunami at Ao Nang, Krabi Province, Thailand
A tsunami (/(t)suːˈnɑːmi, (t)sʊˈ-/ (t)soo-NAH-mee, (t)suu-; from Japanese: 津波, lit. 'harbour wave', pronounced [tsɯnami]) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are in turn generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water from a large event. (Full article...)
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Image credit: Galileo spacecraftThis false-color mosaic showing compositional variations in the geology of the Moon was constructed from a series of 53 images taken through three spectral filters by the imaging system of the Galileo spacecraft. Bright pinkish areas are highlands materials, such as those surrounding the oval lava-filled Mare Crisium impact basin toward the bottom. Blue to orange shades indicate volcanic lava flows. To the left of Crisium, the dark blue Mare Tranquillitatis is richer in titanium than the green and orange maria above it. Thin mineral-rich soils associated with relatively recent impacts are represented by light blue colors. The monochrome band on the right edge shows the unretouched surface of the moon. -
Map: Strebe, using GeocartThe Lambert azimuthal equal-area projection is a projection used for mapping a sphere to a disk. It accurately represents area in all regions of the sphere, but it does not accurately represent angles. It is used in scientific disciplines such as geology for plotting the orientations of lines in three-dimensional space, and by the National Atlas of the US in its online map-making application. -
Map: Grandiose, based on a map by the United States Geological SurveyA geological map of Yosemite National Park (full size), showing the Cathedral Peak Granodiorite, the largest unit in the Tuolumne Intrusive Suite, which in turn is the largest granitic suite in the park.
Cathedral Peak Granodiorite
Rest of the Tuolumne Intrusive Suite -
Curiosity is a car-sized rover designed to explore the crater Gale on Mars as part of NASA's Mars Science Laboratory mission. It was launched from Cape Canaveral in November 2011 and landed on Aeolis Palus inside Gale on August 6, 2012, at 05:17 UTC. Curiosity's landing site, nicknamed Bradbury Landing, was less than 2.4 km (1.5 mi) from the center of the rover's touchdown target after a 560-million km (350-million mi) journey. The rover's goals include an investigation of the Martian climate and geology; assessment of whether the selected field site inside Gale has ever offered environmental conditions favorable for microbial life, including investigation of the role of water; as well as planetary habitability studies in preparation for human exploration.
This picture is a self-portrait of Curiosity on Mars at the "Big Sky" drilling site, where it collected a rock sample at the foothills of Aeolis Mons (Mount Sharp) in October 2015. The photograph combines dozens of images taken by the Mars Hand Lens Imager (MAHLI) camera at the end of the rover's robotic arm; the arm itself is not included, although its shadow is visible on the ground. Wrist motions and turret rotations on the arm allowed MAHLI to acquire the mosaic's component images. -
Cartographic relief depiction showing the varying age of bedrock underlying North America. This image combines a geologic map and a shaded relief image. This combination reveals the geologic history of North America through the interrelation of rock type, topography and time. Regional surface processes as well as continent-scale tectonic events are exposed in the three dimensions of space and the fourth dimension, geologic time. From most recent to oldest, age is indicated by color: yellow, green, blue, red.
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