Earth Sciences, GRE-HYD
The Earth sciences are the fields of study concerned with the solid Earth, its waters, and the air that envelops it. Included are the geologic, hydrologic, and atmospheric sciences.
Earth Sciences Encyclopedia Articles By Title
greenschist facies
greenschist facies, one of the major divisions of the mineral facies classification of metamorphic rocks, the rocks......
Greenwich meridian
Greenwich meridian, an imaginary line, last established in 1851, that was used to indicate 0° longitude. It passes......
Gregale
Gregale, strong and cold wind that blows from the northeast in the western and central Mediterranean region, mainly......
greisen
greisen, modification of granite, an intrusive igneous rock; it consists essentially of quartz and white mica (muscovite)......
grit
grit, sedimentary rock that consists of angular sand-sized grains and small pebbles. The term is roughly equivalent......
grossular
grossular, a calcium aluminum garnet that sometimes resembles the gooseberry fruit. It can be colourless (when......
Groundhog Day
Groundhog Day, in the United States and Canada, day (February 2) on which the emergence of the groundhog (woodchuck)......
groundwater
groundwater, water that occurs below the surface of Earth, where it occupies all or part of the void spaces in......
gummite
gummite, mixture of natural uranium oxides, representing the final oxidation and hydration stages of uraninite,......
Gust
Gust, in meteorology, a sudden increase in wind speed above the average wind speed. More specifically, wind speed......
guyot
guyot, isolated submarine volcanic mountain with a flat summit more than 200 metres (660 feet) below sea level.......
Guzhangian Stage
Guzhangian Stage, last of three internationally defined stages of the Series 3 epoch of the Cambrian Period, encompassing......
gypcrete
gypcrete, gypsum-cemented duricrust, an indurated, or hardened, layer formed on or in soil. It generally occurs......
Gypsisol
Gypsisol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
gypsum
gypsum, common sulfate mineral of great commercial importance, composed of hydrated calcium sulfate (CaSO4·2H2O).......
gyre
gyre, in oceanography and climatology, a vast circular system made up of ocean currents that spirals about a central......
Gzhelian Stage
Gzhelian Stage, last of four internationally defined stages of the Pennsylvanian Subsystem of the Carboniferous......
Géographie Universelle
Géographie Universelle, major French work on regional geography of the entire world. It consists of 15 volumes......
Günz Glacial Stage
Günz Glacial Stage, major division of Pleistocene time and deposits in the Alpine region of Europe (the Pleistocene......
Günz-Mindel Interglacial Stage
Günz-Mindel Interglacial Stage, major division of Pleistocene time and deposits in the Alpine region of Europe......
Haboob
Haboob, strong wind that occurs primarily along the southern edges of the Sahara in Sudan and is associated with......
Hadley cell
Hadley cell, model of the Earth’s atmospheric circulation that was proposed by George Hadley (1735). It consists......
Hail
Hail, precipitation of balls or pieces of ice with a diameter of 5 mm (about 0.2 inch) to more than 15 cm (about......
halide mineral
halide mineral, any of a group of naturally occurring inorganic compounds that are salts of the halogen acids (e.g.,......
halite
halite, naturally occurring sodium chloride (NaCl), common or rock salt. Halite occurs on all continents in beds......
halloysite
halloysite, clay mineral that occurs in two forms: one is similar in composition to kaolinite, and the other is......
Halo
Halo, any of a wide range of atmospheric optical phenomena that result when the Sun or Moon shines through thin......
halocline
halocline, vertical zone in the oceanic water column in which salinity changes rapidly with depth, located below......
halotrichite
halotrichite, a sulfate mineral containing aluminum and iron [FeAl2(SO4)4·22H2O]. If more than 50 percent of the......
Happy Groundhog Day!
All eyes and ears turn to the furry forecaster. spotlight, holiday, american, tradition, groundhog, animal, superstition,...
hardness
hardness, resistance of a mineral to scratching, described relative to a standard such as the Mohs hardness scale.......
Harmattan
Harmattan, cool dry wind that blows from the northeast or east in the western Sahara and is strongest in late fall......
harmotome
harmotome, hydrated barium aluminosilicate mineral, (Ba,Na,K)1–2 (Si,Al)8O16 ∙ 6H2O, in the zeolite family. Harmotome......
Hassi Messaoud
Hassi Messaoud, major oilfield, east-central Algeria. The field lies in the Grand Erg (sand dunes) Oriental of......
hausmannite
hausmannite, a manganese oxide mineral (Mn2+Mn3+2O4) that occurs as brownish black crystals or granular masses......
Hauterivian Stage
Hauterivian Stage, third of six main divisions (in ascending order) of the Lower Cretaceous Series, representing......
Haze
Haze, suspension in the atmosphere of dry particles of dust, salt, aerosols, or photochemical smog that are so......
Heat wave
Heat wave, period of prolonged abnormally high surface temperatures relative to those normally expected. Heat waves......
Heinrich event
Heinrich event, any of a series of at least six large discharges of icebergs that carried coarse-grained rocky......
Hekla
Hekla, active volcano, southern Iceland, lying within the country’s East Volcanic Zone. It is Iceland’s most active......
helium dating
helium dating, method of age determination that depends on the production of helium during the decay of the radioactive......
Hell Creek Formation
Hell Creek Formation, division of rocks in North America dating to the end of the Cretaceous Period some 65.5 million......
hematite
hematite, heavy and relatively hard oxide mineral, ferric oxide (Fe2O3), that constitutes the most important iron......
hemimorphite
hemimorphite, one of two minerals formerly called calamine in the U.S., a white silicate mineral that is an important......
hemisphere
hemisphere, in geometry and geography, half of a sphere. Although any spherical body can be divided into an infinite......
Hettangian Stage
Hettangian Stage, lowest of the four divisions of the Lower Jurassic Series, representing all rocks formed worldwide......
heulandite
heulandite, hydrated sodium and calcium aluminosilicate mineral in the zeolite family, formulated (Ca,Na)2-3Al3(Al,Si)2Si13O36·12H2O.......
Highland climate
Highland climate, major climate type often added to the Köppen classification, although it was not part of German......
Hirnantian Stage
Hirnantian Stage, last of three internationally defined stages of the Upper Ordovician Series, encompassing all......
Histosol
Histosol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
Histosol
Histosol, one of the 12 soil orders in the U.S. Soil Taxonomy. Histosols are formed under waterlogged conditions......
Hoarfrost
Hoarfrost, deposit of ice crystals on objects exposed to the free air, such as grass blades, tree branches, or......
Holstein Interglacial Stage
Holstein Interglacial Stage, major division of Pleistocene deposits and time in Europe (the Pleistocene Epoch began......
Homerian Stage
Homerian Stage, second of two stages of the Wenlock Series, encompassing all rocks deposited during the Homerian......
horizon
horizon, a distinct layer of soil, approximately parallel with the land surface, whose properties develop from......
hornblende
hornblende, calcium-rich amphibole mineral that is monoclinic in crystal structure. Hornblende’s generalized chemical......
hornfels facies
hornfels facies, a major division of metamorphic rocks (rocks that form by contact metamorphism in the inner parts......
Horse latitude
Horse latitude, either of two subtropical atmospheric high-pressure belts that encircle Earth around latitudes......
horst and graben
horst and graben, elongate fault blocks of the Earth’s crust that have been raised and lowered, respectively, relative......
hot spring
hot spring, spring with water at temperatures substantially higher than the air temperature of the surrounding......
hotspot
hotspot, region of Earth’s upper mantle that upwells to melt through the crust to form a volcanic feature. Most......
How are mountains formed?
The most common and visible way mountains are formed is through the convergence of Earth’s tectonic plates. When......
How big is Earth?
Earth has a diameter at the Equator of about 12,756 kilometers (7,926 miles), making it the fifth largest planet......
How do clouds form?
Cloud formation, a key part of the water cycle, begins as moist air ascends into the atmosphere. This occurs because,......
How do earthquakes occur?
Earthquakes occur due to the sudden release of stored energy in Earth’s crust, primarily caused by tectonic movements.......
How Do Hurricanes Get Their Names?
In meteorology, hurricanes and typhoons are regional names for tropical cyclones, and individual storms of each......
How Do Ocean Currents Affect the Biosphere?
Ocean currents are streams of water in the ocean whose circulation is produced by gravity, wind friction, and water......
How Do Scientists Predict Tsunamis After Earthquakes?
Earthquakes, landslides, volcanic eruptions, and even meteoroid and comet strikes can produce tsunamis—trains of......
How do tectonic plates move?
Scientists are still debating how tectonic plates move, but most of experts believe that the movement of plates......
How Do Tornadoes Form?
The average tornado—a mostly harmless cyclone of air that connects a storm cloud above and Earth’s surface below—has......
How does carbon dating work?
Carbon dating, also known as radiocarbon dating or carbon-14 dating, is a technique used to learn the age of organic......
How does fog form?
Fog is a cloud of small water droplets near ground level. It is formed by the condensation of water vapor on tiny......
How fast does a tornado travel?
Tornadoes can travel at speeds of up to 120 km (75 miles) per hour in extreme examples, with an average forward......
How fast does Earth spin?
Earth spins at a velocity of about 1,674 kilometers (1,040 miles) per hour at the Equator. The speed at which Earth......
How fast is lightning?
The visible flash of a lightning strike travels at the speed of light (670 million miles per hour), while the electrical......
How hot can lightning get?
A thunderstorm on a hot summer afternoon might cool down the air outside, but the air around the lightning itself......
How is marble formed?
Marble is formed when limestone or dolomite (rocks composed of calcium magnesium carbonate) recrystallizes under......
How long was the Ice Age?
The most recent major ice age, known as the Great Ice Age or Pleistocene Epoch, spanned approximately 2.6 million......
How many moons does Earth have?
You may have seen headlines such as “NASA confirms Earth now has two moons until 2083.” But we first need to define......
How Much Does Earth’s Atmosphere Weigh?
In 1798 British physicist Henry Cavendish became the first person to accurately determine the mass of Earth. His......
How Old Is Earth?
People and all other known forms of life inhabit one very old planet. In numerical terms, the best estimate of......
How the 1815 Eruption of Mount Tambora Produced the “Year Without a Summer”
Mount Tambora is a stratovolcano and forms the entire 37.3-mile- (60-km-) wide Sanggar peninsula on Sumbawa island,......
How to watch the northern lights
The northern lights, or aurora borealis, occur when particles from the solar wind interact with atoms in the upper......
How was Devils Tower formed?
Scientists agree that Devils Tower was formed through a fascinating geological process involving volcanic activity......
How was Earth created?
Earth’s creation is a fascinating tale of interstellar material coming together to form our planet. It all began......
How was Niagara Falls formed?
Niagara Falls was formed over 12,000 years ago as a result of the melting ice from the retreating glaciers at the......
How was the Grand Canyon formed?
The short answer is the hard work of the Colorado River, but the real answer is more complex. About six million......
How was the Mariana Trench formed?
The Mariana Trench was formed through subduction, a process in which one tectonic plate is forced below another.......
Hudsonian orogeny
Hudsonian orogeny, Precambrian thermal event on the Canadian Shield that took place 1.7 billion years ago (± 1.5......
humic acid
humic acid, one of two classes of natural acidic organic polymer that can be extracted from humus found in soil,......
Humid continental climate
Humid continental climate, major climate type of the Köppen classification that exhibits large seasonal temperature......
Humid subtropical climate
Humid subtropical climate, major climate type of the Köppen classification characterized by relatively high temperatures......
Humidity
Humidity, the amount of water vapor (or moisture) in the air. It is the most variable characteristic of the atmosphere......
humite
humite, member of a group of layered silicate minerals related to the olivines that are nearly always restricted......
humus
humus, nonliving, finely divided organic matter in soil, derived from microbial decomposition of plant and animal......
Hunter-Bowen orogeny
Hunter-Bowen orogeny, a mountain-building event in eastern Australia that began about 265 million years ago during......
Hurricane Katrina 20 Years Later: Disaster, Recovery, & Legacy
Decades after the storm’s passing in August 2005, the wrath of Hurricane Katrina remains etched into the American......
hyacinth
hyacinth, a red, orange, or yellow variety of the gemstone zircon...
hyalophane
hyalophane, a barium-rich variety of potassium feldspar; see...
hydraulic equivalence
hydraulic equivalence, size–density relationship that governs the deposition of mineral particles from flowing......