geological engineering See engineering geology
geology Scientific study of the Earth, including its composition, struc¬ ture, physical properties, and history. Geology is commonly divided into subdisciplines concerned with the chemical makeup of the Earth, includ¬ ing the study of minerals (mineralogy) and rocks (petrology); the structure of the Earth (structural geology) and volcanic phenomena (volcanology); landforms and the processes that produce them (geomorphology and gla¬ ciology); geologic history, including the study of fossils (paleontology), the development of sedimentary strata (stratigraphy), and the evolution of planetary bodies and their satellites (astrogeology); and economic geology and its various branches, such as mining geology and petroleum geology. Some major fields closely allied to geology are geodesy, geophysics, and GEOCHEMISTRY. See also ENVIRONMENTAL GEOLOGY.
geomagnetic field Magnetic field associated with the Earth. It is essentially dipolar (i.e., it has two poles, the northern and southern mag¬ netic poles) on the Earth’s surface. Away from the surface, the field becomes distorted. Most geomagnetists explain the field by means of dynamo theories, whereby a source of energy in the Earth’s core causes a self-sustaining magnetic field. In the dynamo theories, fluid motion in the Earth’s core involves the movement of conducting material within an existing magnetic field, thus creating a current and a self-enforcing field.
geomagnetic reversal Alternation of the Earth’s magnetic polarity. The Earth’s internal magnetic field reverses, on average, about every 300,000 to 1 million years. This reversal is very sudden on a geologic time scale, apparently taking about 5,000 years. The time between rever¬ sals is highly variable, sometimes less than 40,000 years and at other times as long as 35 million years. No regularities or periodicities have yet been discovered. A long interval of one polarity may be followed by a short interval of opposite polarity. See also polar wandering.
geomagnetics Branch of geophysics concerned with all aspects of the Earth’s magnetic field, including its origin, variation through time, and manifestations in the form of magnetic poles, the magnetization of rocks, and local or regional magnetic anomalies.
Geometric style Style of vase painting that flourished in Athens c. 1000-700 bc. Vases decorated in this style feature horizontal bands filled with geometric patterns such as zigzags, triangles, and swastikas in dark paint on a light ground. The rhythmic effect is similar to that of basketry. The abstract motifs developed into stylized animal and human forms in
"The Annunciation," painting by Orazio Gentileschi, 1623; in the Galle¬ ria Sabauda, Turin, Italy
SCALA—ART RESOURCE
© 2006 Encyclopaedia Britannica, Inc.
750 I geometry ► George III
Geologic Time
Eon
Era
Periods and systems
Epochs and series
Beginning of interval*
Biological forms
Phanerozoic
Cenozoic
Quaternary
Holocene
0.01
Pleistocene
1.8
Earliest humans
Tertiary
Pliocene
5
Miocene
24
Earliest hominids
Oligocene
34
Eocene
55
Earliest grasses
Paleocene
65
Earliest large mammals
Cretaceous-Tertiary boundary (65 million years ago): extinction of dinosaurs
Mesozoic
Cretaceous
Late
99
Early
144
Earliest flowering plants; dinosaurs in ascendance
Jurassic
206
Earliest birds and mammals
Triassic
248
Age of Dinosaurs begins
Paleozoic
Permian
290
Carboniferous
Pennsylvanian
323
Earliest reptiles
Mississippian
354
Earliest winged insects
Devonian
417
Earliest vascular plants (incl. ferns and mosses)
and amphibians
Silurian
443
Earliest land plants and insects
Ordovician
490
Earliest corals
Cambrian
543
Earliest fishes
Proterozoic
Precambrian
2,500
Earliest colonial algae and soft-bodied invertebrates
Archean
4,000
Life appears; earliest algae and primitive bacteria
*ln millions of years before the present.
such narrative scenes as funerals, dances, and boxing matches. Small bronze and clay figurines, elaborately decorated fibulas, and limestone seals were also produced. The patterns remained popular and influenced much later Greek art.
geometry See algebraic geometry, analytic geometry, differential geom¬ etry, ELLIPTIC GEOMETRY, EUCUDEAN GEOMETRY, FRACTAL GEOMETRY, HYPERBOLIC GEOM¬ ETRY, non-Euclidean geometry, projective geometry
geomorphology Scientific discipline that describes and classifies the Earth’s topographic features. Many systems of classifying landforms have been devised. Some systems describe and group topographic features pri¬ marily according to the processes that shaped or modified them. Others take additional factors into consideration (e.g., character of the surface rocks and climatic variations) and include the developmental stage of landforms as an aspect of their evolution over geologic time.
geophysics Major branch of earth science that applies the principles and methods of physics to the study of the Earth. Geophysics deals with such geologic phenomena as the temperature distribution of the Earth’s interior; the source, configuration, and variations of the geomagnetic field; and the large-scale features of the terrestrial crust, such as rifts, conti¬ nental sutures, and oceanic ridges. Modem geophysical research also examines phenomena of the outer parts of the Earth’s atmosphere and even the physical properties of other planets and their satellites. See also MARINE GEOPHYSICS.
geopolitics The study of geographic influences on power relationships in international politics. Geopolitical theorists have sought to demonstrate the importance in the determination of foreign policies of considerations such as the acquisition of natural boundaries, access to important sea routes, and the control of strategically important land areas. The term was first employed in the early 20th century by the Swedish political scientist Rudolph Kjellen (1864-1922). Geopolitical factors have become less sig¬ nificant in the foreign policies of states because of improvements in com¬ munications and transportation.
George I orig. George Louis German Georg Ludwig (b. May
28, 1660, Osnabriick, Hanover—d. June 11, 1727, Osnabruck) First king of England (1714-27) from the house of Hanover. He succeeded his father as the elector of Hanover (1698) and fought with distinction in the War of the Spanish Succession. As a great-grandson of James I of England and under the Act of Settlement, George ascended the English throne in 1714. He formed a Whig ministry and left internal politics to his ministers, including 1 st Earl Stanhope, Viscount Townshend, and Robert Walpole. He was unpopular because of his German manner and German mistresses and
their involvement in the South Sea Bubble crisis, but he strengthened Brit¬ ain’s position by forming the Quadruple Alliance (1718). He was suc¬ ceeded by his son, George II.
George I Greek Georgios orig. Prince William of Denmark
(b. Dec. 24, 1845, Copenhagen, Den.—d. March 18, 1913, Salonika, Greece) King of Greece. Son of Christian IX of Denmark, he served in the Danish navy and in 1862 was nominated to the Greek throne by Britain, France, and Russia after the Greek king, Otto, was deposed. Accepted by the Greek National Assembly, he ascended the throne as George 1 in 1863. He oversaw the incorporation of territory in Thessaly and Epirus into Greece as well as the annexation of Crete. In the unrest caused by the Balkan Wars, he was assassinated at Salonika; he was succeeded by his son, Constantine I. His long reign was the formative period for the devel¬ opment of Greece as a modem European state.
George II orig. George Augustus German Georg August (b.