Earth Science, Geologic Time & Fossils, OZA-POL
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
ozarkodiniform, conodont, or small fossil that is toothlike in form and structure, that has a prominent, centrally......
ozone depletion, gradual thinning of Earth’s ozone layer in the upper atmosphere caused by the release of chemical......
ozone layer, region of the upper atmosphere, between roughly 15 and 35 km (9 and 22 miles) above Earth’s surface,......
oölite, ovoid or spherical crystalline deposit with a concentric or radial structure; most are composed of calcium......
Pachycephalosaurus, genus of large and unusual dinosaurs found as fossils in deposits of North America dating to......
Pakicetus, extinct genus of early cetacean mammals known from fossils discovered in 48.5-million-year-old river......
Palaeospondylus, genus of enigmatic fossil vertebrates that were very fishlike in appearance but of uncertain relationships.......
paleoanthropology, interdisciplinary branch of anthropology concerned with the origins and development of early......
paleoceanography, scientific study of Earth’s oceanographic history involving the analysis of the ocean’s sedimentary......
paleoclimatology, scientific study of the climatic conditions of past geologic ages. Paleoclimatologists seek to......
Paleogene Period, oldest of the three stratigraphic divisions of the Cenozoic Era spanning the interval between......
paleogeography, the ancient geography of Earth’s surface. Earth’s geography is constantly changing: continents......
paleogeology, the geology of a region at any given time in the distant past. Paleogeologic reconstructions in map......
paleohydrology, science concerned with hydrologic systems as they existed during previous periods of Earth history.......
paleontology, scientific study of life of the geologic past that involves the analysis of plant and animal fossils,......
Paleozoic Era, major interval of geologic time that began 538.8 million years ago with the Cambrian explosion,......
palladium (Pd), chemical element, the least dense and lowest-melting of the platinum metals of Groups 8–10 (VIIIb),......
Peter Simon Pallas was a German naturalist who advanced a theory of mountain formation and, by the age of 15, had......
palynology, scientific discipline concerned with the study of plant pollen, spores, and certain microscopic planktonic......
Friedrich Adolf Paneth was an Austrian chemist who, with George Charles de Hevesy, introduced radioactive tracer......
Pangea, in early geologic time, a supercontinent that incorporated almost all the landmasses on Earth. Pangea was......
Paradoxides, genus of trilobites (an extinct group of arthropods) found as fossils in Middle Cambrian rocks of......
Parafusulina, genus of extinct fusulinid foraminiferans (single-celled animals with a hard, complexly constructed......
parallel, imaginary line extending around the Earth parallel to the equator; it is used to indicate latitude. The......
Paraschwagerina, genus of extinct fusulinid foraminiferans (protozoans with a relatively large shell readily preservable......
Siegfried Passarge was a geographer and geomorphologist known for his studies of southern Africa. A professor at......
Charles William Peach was an English naturalist and geologist who made valuable contributions to the knowledge......
pedology, scientific discipline concerned with all aspects of soils, including their physical and chemical properties,......
pegmatite, almost any wholly crystalline igneous rock that is at least in part very coarse grained, the major constituents......
Albrecht Penck was a geographer, who exercised a major influence on the development of modern German geography,......
William Pengelly was an English educator, geologist, and a founder of prehistoric archaeology whose excavations......
Peninj mandible, an almost perfectly preserved fossil jaw of the hominin (of human lineage) species Paranthropus......
Richard Alexander Fullerton Penrose, Jr. was a geologist known for his explorations for manganese and iron-ore......
pentlandite, a nickel and iron sulfide mineral, the chief source of nickel. It is nearly always found with pyrrhotite......
Pentremites, extinct genus of stemmed, immobile echinoderms (forms related to the starfish) abundant as marine......
periclase, magnesium oxide mineral (MgO) that occurs as colourless to grayish, glassy, rounded grains in marble......
peridotite, a coarse-grained, dark-coloured, heavy, intrusive igneous rock that contains at least 10 percent olivine,......
periglaciology, study of the large areas of the Earth that were adjacent to but not covered by ice during the glacial......
period, in geology, the basic unit of the geologic time scale; during these spans of time specific systems of rocks......
perlite, a natural glass with concentric cracks such that the rock breaks into small pearl-like bodies. It is formed......
permeability, capacity of a porous material for transmitting a fluid; it is expressed as the velocity with which......
Permian Period, in geologic time, the last period of the Paleozoic Era. The Permian Period began 298.9 million......
perovskite, calcium titanate mineral (CaTiO3) found as brilliant black cubes in many mafic igneous rocks, in their......
Petralona skull, an ancient human cranium discovered in 1960 in a cave near Thessaloníki, northeastern Greece.......
Petrified Forest National Park, desert area containing plant and animal fossils and archaeological sites in eastern......
petrified wood, fossil formed by the invasion of minerals into cavities between and within cells of natural wood,......
petrology, scientific study of rocks that deals with their composition, texture, and structure; their occurrence......
Sverre Petterssen was a meteorologist who specialized in both dynamic meteorology, concerned with atmospheric motions......
Phacops, genus of trilobites (an extinct group of aquatic arthropods) found as fossils in Silurian and Devonian......
Phaeozem, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
Phanerozoic Eon, the span of geologic time extending about 541 million years from the end of the Proterozoic Eon......
pharmacosiderite, hydrated iron arsenate mineral (KFe3+4(AsO4)3(OH)4·6−7H2O) that forms olive-green to honey-yellow,......
Phenacodus, extinct genus of mammals known from fossils of the late Paleocene and early Eocene epochs of North......
phenakite, rare mineral, beryllium silicate, Be2SiO4, used as a gemstone. Phenakite has long been known from the......
Phillipsia, genus of trilobites (an extinct group of aquatic arthropods) uncommonly found as fossils in Carboniferous......
Phoberomys, extinct rodent genus, the largest rodent ever to have lived, that belongs to the infraorder Caviomorpha,......
phonolite, any member of a group of extrusive igneous rocks (lavas) that are rich in nepheline and potash feldspar.......
phosphate mineral, any of a group of naturally occurring inorganic salts of phosphoric acid, H3(PO4). More than......
phosphorite, rock with a high concentration of phosphates in nodular or compact masses. The phosphates may be derived......
phyllite, fine-grained metamorphic rock formed by the reconstitution of fine-grained, parent sedimentary rocks,......
Phyllograptus, genus of graptolites, an extinct group of small colonial marine animals related to the primitive......
phyllosilicate, compound with a structure in which silicate tetrahedrons (each consisting of a central silicon......
physical geology, scientific discipline that is concerned with all aspects of the Earth’s structure, composition,......
phytosaur, heavily armoured semiaquatic reptiles found as fossils from the Late Triassic Period (about 229 million......
Bertrand Piccard is a Swiss aviator who on March 20, 1999, with copilot Brian Jones, completed the first nonstop......
pickeringite, magnesium-rich variety of the mineral halotrichite MgAl2(So4)4·22Η2Ο...
picrite, intrusive igneous rock of ultramafic (very silica-poor) composition that is composed largely of olivine......
Piltdown man, (Eoanthropus dawsoni), proposed species of extinct hominin (member of the human lineage) whose fossil......
Louis Valentine Pirsson was a geologist whose studies of the igneous rocks of Montana revealed many previously......
pisolite, spheroidal crystalline particle larger than 2 millimetres in diameter (see...
pitchstone, a volcanic glass with a conchoidal fracture (like glass), a resinous lustre, and a variable composition.......
placoderm, any member of an extinct group (Placodermi) of primitive jawed fishes known only from fossil remains.......
planet, (from Greek planētes, “wanderers”), broadly, any relatively large natural body that revolves in an orbit......
planetary boundary layer (PBL), the region of the lower troposphere where Earth’s surface strongly influences temperature,......
Planosol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
plasmapause, portion of the magnetosphere that rotates with the Earth at about four Earth radii (approximately......
plate tectonics, theory dealing with the dynamics of Earth’s outer shell—the lithosphere—that revolutionized Earth......
- Introduction
- Earth's Layers, Crust, Mantle
- Seafloor Spreading, Continental Drift, Subduction
- Island Arcs, Subduction, Volcanism
- Transform Faults, Continental Drift, Subduction
- Development, Theory, Earth
- Continental Drift, Subduction, Earthquakes
- Hess's Model, Seafloor Spreading, Continental Drift
- Continental Drift, Subduction, Earthquakes
- Seismic Tomography, Earth's Crust, Subduction
- Continental Drift, Subduction, Earthquakes
- Continental Reconstructions
- Extinction, Continental Drift, Subduction
platinum (Pt), chemical element, the best known and most widely used of the six platinum metals of Groups 8–10,......
Platyceras, genus of extinct gastropods (snails) that occurs as fossils in rocks of Silurian to Permian age (about......
Platycrinites, genus of extinct crinoids, or sea lilies, especially characteristic as fossils of Early Carboniferous......
Platystrophia, genus of extinct brachiopods (lamp shells) occurring as fossils in marine rocks of the Middle Ordovician......
John Playfair was a Scottish geologist and mathematician known for his explanation and expansion of ideas on uniformitarianism—the......
Plectoceras, extinct genus of small marine nautiloid cephalopods, forms related to the modern pearly nautilus,......
pleochroic halo, ring of colour produced around a radioactive impurity included in a mineral by alpha particles......
plesiosaur, (clade Plesiosauria), any of a group of long-necked marine reptiles found as fossils from the late......
Pleuromeia, genus of extinct lycopsid plants from the Triassic Period (about 251 million to 200 million years ago)......
Plinthosol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
Pliohippus, extinct genus of horses that inhabited North America during the Pliocene Epoch (5.3–2.6 million years......
pliosaur, a group of large carnivorous marine reptiles characterized by massive heads, short necks, and streamlined......
plumbojarosite, a widespread iron and lead sulfate mineral, PbFe6(So4)4(OH)12, that has been found in the oxidized......
pluton, body of intrusive igneous rock the size, composition, shape, or exact type of which is in doubt; when such......
Plymouth Rock, granite slab upon which, according to tradition, the Pilgrim Fathers stepped first after disembarking......
Podzol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
podzolic soil, soil usually forming in a broadleaf forest and characterized by moderate leaching, which produces......
polar air mass, air mass that forms over land or water in the higher latitudes. See air mass;...
polar anticyclone, wind system associated with a region in which high atmospheric pressure develops over or in......
polar front, in meteorology, the transition region separating warmer tropical air from colder polar air in the......
polar region, area around the North Pole or the South Pole. The northern polar region consists mainly of floating......
polar vortex, large area of persistent low pressure generally located above each of Earth’s polar regions and containing......
polar wandering, the migration of the magnetic poles over Earth’s surface through geologic time. The study of polar......