Geology is the study of the Earth’s composition, structure, processes, and history. It is one of the major Earth sciences, which examine questions relating to the planet Earth. This node will look briefly at some of the major branches of geology: mineralogy, petrology, palaeontology, plate tectonics, geophysics, geochemistry, and planetary and marine geology.


Structure of the Earth

 The Earth is made of three main layers: the crust, mantle, and core. The outer solid crust surrounds the mantle, and is between 3 and 6.8 miles thick under the oceans, and 12 to 40 miles thick under the continents.

The mantle makes up the majority of the Earth’s volume and mass, and consists of molten rock 1,802 miles thick.

The Earth’s core is 2,200 miles thick, and is composed mainly of iron, partly liquid and partly solid.



Mineralogy attempts to describe the crystal structure, chemistry, and physical properties of minerals, including their creation and destruction. Geologists look at certain features of minerals known as cleavage, colour, crystal shape, fracture, hardness, specific gravity, streak, and striations.



Petrology studies rocks, which are aggregates of minerals, and the conditions they form in. Petrology focuses its attention on the three types of rocks: igneous, metamorphic and sedimentary rocks.



Paleontology is the study of ancient life on earth, based on fossils. Physical anthropology also examines human fossils and their evolution.


Plate tectonics

The theory of plate tectonics states that the lithosphere is divided into plates which interact with each other and float around the planed on the asthenosphere. This helps explain continental drift and the Ring of Fire, which is marked by frequent earthquakes and volcanoes.



Geophysics is the science of physics as it applies to geology, and includes the measurement of seismic movements, geodesy, gravity, magnetism, electricity, electromagnetism, and radioactivity.



In a similar way, geochemistry is the science of chemistry as it applies to geology. It looks at absolute and relative abundances of the chemical elements and their isotopes in the Earth, and also the chemical changes that accompany geologic processes.


Planetary geology

Planetary geology, as its name suggests, involves the study of planets and moons other than the Earth itself, for instance, Mars, Venus, and the moons of Saturn and Jupiter. Planetary geologists place great emphasis on the results of space probes to provide information.


Marine geology

Marine geology looks in particular at ocean floors and coastlines, and uses geophysics, geochemistry, sedimentology and paleontology to aid its research. Its studies also have links with oceanography and plate tectonics.



Hutchison Encyclopedia, Research Machines plc, 2004
New York Public Library Science Desk Reference, Stonesong Press Inc, 1995
Minerals, Rocks, and Fossils, Reed International Books Ltd, 1974

Ge*ol"o*gy (?), n.; pl. Geologies (#). [Gr. , , the earth + -logy: cf. F. g'eologie.]


The science which treats: (a) Of the structure and mineral constitution of the globe; structural geology. (b) Of its history as regards rocks, minerals, rivers, valleys, mountains, climates, life, etc.; historical geology. (c) Of the causes and methods by which its structure, features, changes, and conditions have been produced; dynamical geology. See Chart of The Geological Series.


A treatise on the science.


© Webster 1913.

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