Earth Science, Geologic Time & Fossils, NOT-PHY
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 Earthâs crust, oceans, and atmosphere.
Earth Science, Geologic Time & Fossils Encyclopedia Articles By Title
Nothosaurus
Nothosaurus, (genus Nothosaurus), marine reptiles found as fossils from the Triassic Period (251 million to 200......
Notoungulata
Notoungulata, extinct group of hoofed mammals found as fossils, mostly in South America, although the oldest forms......
Nuclear winter
Nuclear winter, the environmental devastation that certain scientists contend would probably result from the hundreds......
nummulite
nummulite, any of the thousands of extinct species of relatively large, lens-shaped foraminifers (single-celled......
Nunes, Pedro
Pedro Nunes was a mathematician, geographer, and the chief figure in Portuguese nautical science, noted for his......
Obolus
Obolus, genus of extinct brachiopod, or lamp shell, of the Cambrian Period (from 542 million to 488 million years......
obsidian
obsidian, igneous rock occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes.......
obsidianâhydrationârind dating
obsidianâhydrationârind dating, method of age determination of obsidian (black volcanic glass) that makes use of......
ocean
ocean, continuous body of salt water that is contained in enormous basins on Earthâs surface. When viewed from......
ocean acidification
ocean acidification, the worldwide reduction in the pH of seawater as a consequence of the absorption of large......
Ocean Acidification: How Carbon Dioxide Is Hurting the Seas
The Keeling Curve is one of climatologyâs most enduring and useful tools. Itâs a graph that has tracked seasonal......
ocean current
ocean current, stream made up of horizontal and vertical components of the circulation system of ocean waters that......
Ocean fertilization
Ocean fertilization, untested geoengineering technique designed to increase the uptake of carbon dioxide (CO2)......
ocean warming
ocean warming, the absorption of surplus heat attributed to global warming by water in the oceans. Ocean warming......
oceanography
oceanography, scientific discipline concerned with all aspects of the worldâs oceans and seas, including their......
Odessa Meteor Crater
Odessa Meteor Crater, shallow, cone-shaped impact crater in the High Plains just southwest of Odessa, Texas, U.S.,......
odontolite
odontolite, fossil bone or tooth that consists of the phosphate mineral apatite (q.v.) coloured blue by vivianite.......
Oldham, Richard Dixon
Richard Dixon Oldham was a British geologist and seismologist who discovered evidence for the existence of the......
Olenellus
Olenellus, genus of trilobites (extinct arthropods) common in but restricted to Early Cambrian rocks (542 million......
olivine
olivine, any member of a group of common magnesium, iron silicate minerals. Olivines are an important rock-forming......
Omalius dâHalloy, Jean-Baptiste-Julien dâ
Jean-Baptiste-Julien dâ Omalius dâHalloy was a Belgian geologist who was an early proponent of evolution. DâOmalius......
Oppel, Albert
Albert Oppel was a German geologist and paleontologist, who was one of the most important early stratigraphers.......
Orbigny, Alcide Dessalines dâ
Alcide Dessalines dâ Orbigny was the founder of the science of micropaleontology. During eight years of travel......
Ordovician Period
Ordovician Period, in geologic time, the second period of the Paleozoic Era. It began 485.4 million years ago,......
oreodont
oreodont, any member of a diverse group of extinct herbivorous North American artiodactyls (even-toed ungulates)......
Oreopithecus
Oreopithecus, extinct genus of primates found as fossils in Late Miocene deposits in East Africa and Early Pliocene......
ornithischian
ornithischian, any member of the large taxonomic group of herbivorous dinosaurs comprising Triceratops and all......
Ornithomimus
Ornithomimus, (genus Ornithomimus), ostrichlike feathered dinosaurs found as fossils in Mongolian, European, and......
ornithopod
ornithopod, any member of the group of ornithischian dinosaurs characterized by a two-legged (bipedal) stance,......
Orographic precipitation
Orographic precipitation, rain, snow, or other precipitation produced when moist air is lifted as it moves over......
orpiment
orpiment, the transparent yellow mineral arsenic sulfide (As2S3), formed as a hot-springs deposit, an alteration......
orthopyroxene granite
orthopyroxene granite, member of the charnockite (q.v.) series of metamorphic...
Osborn, Henry Fairfield
Henry Fairfield Osborn was an American paleontologist, eugenicist, and museum administrator who greatly influenced......
Osteolepis
Osteolepis, extinct genus of lobe-finned fishes from the Late Devonian; Osteolepiformes is a variation of this......
Ostrom, John
John Ostrom was an American paleontologist who popularized the theory that many species of dinosaurs were warm-blooded......
Ouachita Geosyncline
Ouachita Geosyncline, a linear trough in the Earthâs crust in which rocks of the Paleozoic Era (from 542 million......
Owen, Richard
Richard Owen was a British anatomist and paleontologist who is remembered for his contributions to the study of......
oxide mineral
oxide mineral, any naturally occurring inorganic compound with a structure based on close-packed oxygen atoms in......
Oxisol
Oxisol, one of the 12 soil orders in the U.S. Soil Taxonomy. Oxisols form principally in humid tropical zones under......
ozarkodiniform
ozarkodiniform, conodont, or small fossil that is toothlike in form and structure, that has a prominent, centrally......
Ozone depletion
Ozone depletion, gradual thinning of Earthâs ozone layer in the upper atmosphere caused by the release of chemical......
Ozone layer
Ozone layer, region of the upper atmosphere, between roughly 15 and 35 km (9 and 22 miles) above Earthâs surface,......
oölite
oölite, ovoid or spherical crystalline deposit with a concentric or radial structure; most are composed of calcium......
Pachycephalosaurus
Pachycephalosaurus, genus of large and unusual dinosaurs found as fossils in deposits of North America dating to......
Pakicetus
Pakicetus, extinct genus of early cetacean mammals known from fossils discovered in 48.5-million-year-old river......
Palaeospondylus
Palaeospondylus, genus of enigmatic fossil vertebrates that were very fishlike in appearance but of uncertain relationships.......
paleoanthropology
paleoanthropology, interdisciplinary branch of anthropology concerned with the origins and development of early......
paleoceanography
paleoceanography, scientific study of Earthâs oceanographic history involving the analysis of the oceanâs sedimentary......
Paleoclimatology
Paleoclimatology, scientific study of the climatic conditions of past geologic ages. Paleoclimatologists seek to......
Paleogene Period
Paleogene Period, oldest of the three stratigraphic divisions of the Cenozoic Era spanning the interval between......
paleogeography
paleogeography, the ancient geography of Earthâs surface. Earthâs geography is constantly changing: continents......
paleogeology
paleogeology, the geology of a region at any given time in the distant past. Paleogeologic reconstructions in map......
paleohydrology
paleohydrology, science concerned with hydrologic systems as they existed during previous periods of Earth history.......
paleontology
paleontology, scientific study of life of the geologic past that involves the analysis of plant and animal fossils,......
Paleozoic Era
Paleozoic Era, major interval of geologic time that began 538.8 million years ago with the Cambrian explosion,......
palladium
palladium (Pd), chemical element, the least dense and lowest-melting of the platinum metals of Groups 8â10 (VIIIb),......
Pallas, Peter Simon
Peter Simon Pallas was a German naturalist who advanced a theory of mountain formation and, by the age of 15, had......
palynology
palynology, scientific discipline concerned with the study of plant pollen, spores, and certain microscopic planktonic......
Paneth, Friedrich Adolf
Friedrich Adolf Paneth was an Austrian chemist who, with George Charles de Hevesy, introduced radioactive tracer......
Pangea
Pangea, in early geologic time, a supercontinent that incorporated almost all the landmasses on Earth. Pangea was......
Paradoxides
Paradoxides, genus of trilobites (an extinct group of arthropods) found as fossils in Middle Cambrian rocks of......
Parafusulina
Parafusulina, genus of extinct fusulinid foraminiferans (single-celled animals with a hard, complexly constructed......
parallel
parallel, imaginary line extending around the Earth parallel to the equator; it is used to indicate latitude. The......
Paraschwagerina
Paraschwagerina, genus of extinct fusulinid foraminiferans (protozoans with a relatively large shell readily preservable......
Passarge, Siegfried
Siegfried Passarge was a geographer and geomorphologist known for his studies of southern Africa. A professor at......
Peach, Charles William
Charles William Peach was an English naturalist and geologist who made valuable contributions to the knowledge......
pedology
pedology, scientific discipline concerned with all aspects of soils, including their physical and chemical properties,......
pegmatite
pegmatite, almost any wholly crystalline igneous rock that is at least in part very coarse grained, the major constituents......
Penck, Albrecht
Albrecht Penck was a geographer, who exercised a major influence on the development of modern German geography,......
Pengelly, William
William Pengelly was an English educator, geologist, and a founder of prehistoric archaeology whose excavations......
Peninj mandible
Peninj mandible, an almost perfectly preserved fossil jaw of the hominin (of human lineage) species Paranthropus......
Penrose, Richard Alexander Fullerton, Jr.
Richard Alexander Fullerton Penrose, Jr. was a geologist known for his explorations for manganese and iron-ore......
pentlandite
pentlandite, a nickel and iron sulfide mineral, the chief source of nickel. It is nearly always found with pyrrhotite......
Pentremites
Pentremites, extinct genus of stemmed, immobile echinoderms (forms related to the starfish) abundant as marine......
periclase
periclase, magnesium oxide mineral (MgO) that occurs as colourless to grayish, glassy, rounded grains in marble......
peridotite
peridotite, a coarse-grained, dark-coloured, heavy, intrusive igneous rock that contains at least 10 percent olivine,......
periglaciology
periglaciology, study of the large areas of the Earth that were adjacent to but not covered by ice during the glacial......
period
period, in geology, the basic unit of the geologic time scale; during these spans of time specific systems of rocks......
perlite
perlite, a natural glass with concentric cracks such that the rock breaks into small pearl-like bodies. It is formed......
permeability
permeability, capacity of a porous material for transmitting a fluid; it is expressed as the velocity with which......
Permian Period
Permian Period, in geologic time, the last period of the Paleozoic Era. The Permian Period began 298.9 million......
perovskite
perovskite, calcium titanate mineral (CaTiO3) found as brilliant black cubes in many mafic igneous rocks, in their......
Petralona skull
Petralona skull, an ancient human cranium discovered in 1960 in a cave near ThessalonĂki, northeastern Greece.......
Petrified Forest National Park
Petrified Forest National Park, desert area containing plant and animal fossils and archaeological sites in eastern......
petrified wood
petrified wood, fossil formed by the invasion of minerals into cavities between and within cells of natural wood,......
petrology
petrology, scientific study of rocks that deals with their composition, texture, and structure; their occurrence......
Petterssen, Sverre
Sverre Petterssen was a meteorologist who specialized in both dynamic meteorology, concerned with atmospheric motions......
Phacops
Phacops, genus of trilobites (an extinct group of aquatic arthropods) found as fossils in Silurian and Devonian......
Phaeozem
Phaeozem, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
Phanerozoic Eon
Phanerozoic Eon, the span of geologic time extending about 541 million years from the end of the Proterozoic Eon......
pharmacosiderite
pharmacosiderite, hydrated iron arsenate mineral (KFe3+4(AsO4)3(OH)4·6â7H2O) that forms olive-green to honey-yellow,......
Phenacodus
Phenacodus, extinct genus of mammals known from fossils of the late Paleocene and early Eocene epochs of North......
phenakite
phenakite, rare mineral, beryllium silicate, Be2SiO4, used as a gemstone. Phenakite has long been known from the......
Phillipsia
Phillipsia, genus of trilobites (an extinct group of aquatic arthropods) uncommonly found as fossils in Carboniferous......
Phoberomys
Phoberomys, extinct rodent genus, the largest rodent ever to have lived, that belongs to the infraorder Caviomorpha,......
phonolite
phonolite, any member of a group of extrusive igneous rocks (lavas) that are rich in nepheline and potash feldspar.......
phosphate mineral
phosphate mineral, any of a group of naturally occurring inorganic salts of phosphoric acid, H3(PO4). More than......
phosphorite
phosphorite, rock with a high concentration of phosphates in nodular or compact masses. The phosphates may be derived......
phyllite
phyllite, fine-grained metamorphic rock formed by the reconstitution of fine-grained, parent sedimentary rocks,......
Phyllograptus
Phyllograptus, genus of graptolites, an extinct group of small colonial marine animals related to the primitive......