Earth Science, Geologic Time & Fossils, HIL-IRI
Planet Earth has billions of years of history, from the time when it was an inhospitable ball of hot magma to when its surface stabilized into a variety of diverse zones capable of supporting many life-forms. Many are the species that lived through the various geologic eras and left a trace of their existence in the fossils that we study today. But Earth is never done settling, as we can see from the earthquakes, tsunamis, volcanic eruptions, and other phenomena manifested in Earth’s crust, oceans, and atmosphere.
Earth Science, Geologic Time & Fossils Encyclopedia Articles By Title
Hill, Dorothy
Dorothy Hill was an Australian geologist known for her seminal work on corals dating to the Paleozoic Era (roughly......
Hipparchus
Hipparchus was a Greek astronomer and mathematician who made fundamental contributions to the advancement of astronomy......
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......
Holste, Luc
Luc Holste was a classical scholar and Vatican librarian best known for his annotated editions of geographical......
Homo erectus
Homo erectus, extinct species of the human genus (Homo), perhaps an ancestor of modern humans (Homo sapiens). H.......
Homo floresiensis
Homo floresiensis, taxonomic name given to an extinct hominin (member of the human lineage) that is presumed to......
Homo habilis
Homo habilis, extinct species of human, the most ancient representative of the human genus, Homo. Homo habilis......
Homo heidelbergensis
Homo heidelbergensis, extinct species of archaic human (genus Homo) known from fossils dating from 600,000 to 200,000......
Homo naledi
Homo naledi, extinct species of human, initially thought to have evolved about the same time as the emergence of......
horizon
horizon, a distinct layer of soil, approximately parallel with the land surface, whose properties develop from......
horn coral
horn coral, any coral of the order Rugosa, which first appeared in the geologic record during the Ordovician Period,......
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......
How are fossils formed?
Fossils are most often formed from organisms that have a solid and resistant skeleton. Hard parts, such as bones......
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 Big Was the Asteroid That Contributed to Dinosaur Extinction?
Many scientists believe an asteroid that struck Earth 66 million years ago may have significantly contributed to......
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 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 We Know That Dinosaurs May Have Had Feathers?
Modern birds are living dinosaurs, having evolved from a line of theropod dinosaurs more than 150 million years......
How Do We Know What Dinosaurs Sounded Like?
All animals make sounds. Many sounds are made as an animal moves through its environment, such as the thud or patter......
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 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 is marble formed?
Marble is formed when limestone or dolomite (rocks composed of calcium magnesium carbonate) recrystallizes under......
How long did dinosaurs live?
Dinosaurs roamed the Earth for an impressive span of about 165 to 180 million years. They first appeared about......
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......
Hrdlička, Aleš
Aleš Hrdlička was a physical anthropologist known for his studies of Neanderthal man and his theory of the migration......
Hubbert, Marion King
Marion King Hubbert was an American geophysicist and geologist known for his theory of the migration of fluids......
Humboldt, Alexander von
Alexander von Humboldt was a German naturalist and explorer who was a major figure in the classical period of physical......
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......
Humphreys, William Jackson
William Jackson Humphreys was an American atmospheric physicist who applied basic physical laws to explain the......
humus
humus, nonliving, finely divided organic matter in soil, derived from microbial decomposition of plant and animal......
Huntington, Ellsworth
Ellsworth Huntington was a U.S. geographer who explored the influence of climate on civilization. An instructor......
Huronian System
Huronian System, major division of Precambrian rocks in North America (the Precambrian began about 3.8 billion......
Hutton, James
James Hutton was a Scottish geologist, chemist, naturalist, and originator of one of the fundamental principles......
Huxley, Thomas Henry
Thomas Henry Huxley was an English biologist, educator, and advocate of agnosticism (he coined the word). Huxley’s......
Hyaenodon
Hyaenodon, extinct genus of carnivorous mammals that first appeared in the fossil record about 42 million years......
Hyatt, Alpheus
Alpheus Hyatt was an American zoologist and paleontologist who achieved eminence in the study of invertebrate fossil......
hydraulic equivalence
hydraulic equivalence, size–density relationship that governs the deposition of mineral particles from flowing......
hydrologic sciences
hydrologic sciences, the fields of study concerned with the waters of Earth. Included are the sciences of hydrology,......
- Introduction
- Interception, Precipitation, Runoff
- Groundwater, Aquifers, Recharge
- Catchment Hydrology, Modeling, Simulation
- Lakes, Ecology, Limnology
- Lakes, Water Quality, Ecology
- Ocean Circulation, Water Cycle, Marine Ecosystems
- Glaciology, Hydrology, Geomorphology
- Water Management, Conservation, Floods
- Droughts, Climatic Patterns, Water Cycle
hydrology
hydrology, scientific discipline concerned with the waters of the Earth, including their occurrence, distribution,......
Hydrometeor
Hydrometeor, any water or ice particles that have formed in the atmosphere or at the Earth’s surface as a result......
Hydrometeorology
Hydrometeorology, branch of meteorology that deals with problems involving the hydrologic cycle, the water budget,......
hydrosphere
hydrosphere, discontinuous layer of water at or near Earth’s surface. It includes all liquid and frozen surface......
- Introduction
- Biogeochemical, Water Cycle, Oceans
- Rivers, Oceans, Waters
- Congruent, Incongruent, Weathering
- Lakes, Water Cycle, Ecosystems
- Groundwater, Aquifers, Recharge
- Water Cycle, Oceans, Atmosphere
- Cycle, Evaporation, Precipitation
- Precipitation, Distribution, Water Cycle
- Water Cycle, Oceans, Atmosphere
- Water Cycle, Oceans, Atmosphere
- Sodium Imbalance, Water Cycle, Oceans
- Pollution, Climate Change, Conservation
- Greenhouse Gases, Climate Change, Oceans
hydroxylapatite
hydroxylapatite, phosphate mineral, calcium hydroxide phosphate [Ca5(PO4)3OH], that forms glassy, often green crystals......
Hygrometer
Hygrometer, instrument used in meteorological science to measure the humidity, or amount of water vapor in the......
hypsometric curve
hypsometric curve, cumulative height frequency curve for the Earth’s surface or some part thereof. A hypsometric......
hälleflinta
hälleflinta, (Swedish: “rock flint”), white, gray, yellow, greenish, or pink fine-grained rock that consists of......
hübnerite
hübnerite, manganese-rich variety of the mineral wolframite...
Icadyptes
Icadyptes, genus of extinct giant penguin that lived about 37 million to 35 million years ago, during the second......
ice age
ice age, any geologic period during which thick ice sheets cover vast areas of land. Such periods of large-scale......
ice formation
ice formation, any mass of ice that occurs on the Earth’s continents or surface waters. Such masses form wherever......
ice shelf
ice shelf, thick mass of floating ice that is attached to land, formed from and fed by tongues of glaciers extending......
Ice storm
Ice storm, weather event characterized by rain freezing on contact with cold surfaces that results in ice accumulations......
Icelandic low
Icelandic low, large persistent atmospheric low-pressure centre that forms between Iceland and southern Greenland.......
Ichthyornis
Ichthyornis, (order Ichthyornithiformes), extinct seabird of the Late Cretaceous Period (99.6 million to 66 million......
ichthyosaur
ichthyosaur, any member of an extinct group of aquatic reptiles, most of which were very similar to porpoises in......
Ichthyostega
Ichthyostega, genus of extinct animals, closely related to tetrapods (four-legged land vertebrates) and found as......
Ida
Ida, (Darwinius masillae), nickname for the remarkably complete but nearly two-dimensional skeleton of an adapiform......
Iddings, Joseph Paxson
Joseph Paxson Iddings was an American geologist who demonstrated the genetic relationships of neighbouring igneous......
Idrīsī, Muḥammad al-
Muḥammad al-Idrīsī was an Arab geographer and adviser to Roger II, the Norman king of Sicily. He wrote one of the......
Idrīsī, Muḥammad al-
Muḥammad al-Idrīsī was an Arab geographer and adviser to Roger II, the Norman king of Sicily. He wrote one of the......
igneous rock
igneous rock, any of various crystalline or glassy rocks formed by the cooling and solidification of molten earth......
- Introduction
- Minerals, Magma, Crystals
- Granular, Magma, Crystals
- Intrusive, Extrusive, Textures
- Clastic Structures
- Plutonic, Classification, Rocks
- Volcanic, Hypabyssal, Classification
- Magma Types, Formation, Composition
- Albite, Anorthite, System
- Assimilation, Magma, Crystallization
- Intrusive, Magma, Plutonic
- Convergent Plate, Magma, Intrusive
ijolite
ijolite, intrusive igneous rock that is composed essentially of nepheline and an alkali pyroxene, usually aegirine-augite.......
illuviation
illuviation, Accumulation of dissolved or suspended soil materials in one area or layer as a result of leaching......
Ilmarinen
Ilmarinen, one of the chief deities in Finno-Ugric religion, functioning both as creator deity and as weather god.......
impact structure
impact structure, remains of an ancient meteorite impact on Earth’s surface, generally in the form of a circular......
Inceptisol
Inceptisol, one of the 12 soil orders in the U.S. Soil Taxonomy. Inceptisols are soils of relatively new origin......
index fossil
index fossil, any animal or plant preserved in the rock record of the Earth that is characteristic of a particular......
Indricotherium
Indricotherium, genus of giant browsing perissodactyls found as fossils in Asian deposits of the Late Oligocene......
induration
induration, hardening of rocks by heat or baking; also the hardening of sediments through cementation or compaction,......
inosilicate
inosilicate, any of a class of inorganic compounds that have structures characterized by silicate tetrahedrons......
Institut Géographique National
Institut Géographique National (IGN), one of the foremost centres of mapmaking and geographic research in France,......
internal wave
internal wave, a type of gravity wave that occurs on internal “surfaces” within ocean waters. These surfaces represent......
International Council for the Exploration of the Sea
International Council for the Exploration of the Sea (ICES), international organization that promotes marine research......
International Geographical Union
International Geographical Union (IGU), international body of geographers, founded in 1922, with a membership representing......
International Geophysical Year
International Geophysical Year (IGY), worldwide program of geophysical research that was conducted from July 1957......
intrusive rock
intrusive rock, igneous rock formed from magma forced into older rocks at depths within the Earth’s crust, which......
inyoite
inyoite, a colourless and transparent borate mineral (CaB3O3(OH)5·4H2O) that occurs as massive granular or sperulitic......
Ionosphere and magnetosphere
Ionosphere and magnetosphere, regions of Earth’s atmosphere in which the number of electrically charged particles—ions......
iridescence
iridescence, interference of light either at the surface or in the interior of a material that produces a series......