GEOLOGY. — The introduction (1603) of the term g. (from γῆ, earth, and λόγος, discourse, treatise, history) is attributed to the great naturalist and philosopher Ulisse Aldrovandi. From the very broad field of doctrines that this term initially embraced and long continued to encompass, geology progressively narrowed its boundaries, especially during the nineteenth century, as certain branches detached themselves and came to constitute new fields of science. But the clear and definitive delimitation of the scope of geology, understood in its strictest sense as pure geology, is even more recent.
Presupposing knowledge of rocks (lithology, petrography) and fossils (paleontology), geology may therefore be defined as the science that studies above all the structural characteristics of the earth’s crust (lithosphere), that is, the conditions of development and mutual position (mode of occurrence) of rocks of different nature and origin, which form the crust itself, as well as the processes and causes that have led to its present configuration and reflect the events through which the earth has passed during the immensely long geological ages.
It would nevertheless be impossible to arrive at a reconstruction of these events that was not excessively incomplete and often wholly erroneous if one relied exclusively on the evidence obtainable from the nature, distribution, and mutual mode of occurrence of rock formations.
To achieve this purpose, indispensable documentation can be found only in fossils, that is, in the remains of plant and animal organisms that lived in past ages. These remains, present within sedimentary rocks of all geological ages and often in a state of remarkable preservation, make it possible to reconstruct the characteristics and succession of extinct faunas and floras, as well as the physical environment in which their lives unfolded; they also provide elements for representing the nature of the phenomena that, in an unceasing succession, have progressively altered the features of our planet.
The studies and investigations that lead, or tend to lead, to the achievement of the objectives just mentioned constitute the essence of geology understood in its most restricted and genuine sense. Thus delimited, geology comprises two fundamental parts: structural geology and historical geology, also designated respectively by the names tectonics and stratigraphy.
The former deals with the extremely varied ways in which rocks are arranged within the complex structure of the lithosphere, establishing their most characteristic types with reference to the three categories into which rocks are grouped on the basis of their genesis: eruptive or igneous, sedimentary or stratified, and metamorphic.
Historical geology, or stratigraphy, has as its principal objective the reconstruction of the history of our planet by determining the “relative age” of the rocks that form the framework of the earth’s crust.
It may be said that there is no science, apart from the basic sciences of petrography and paleontology, from which geology does not derive some assistance for its objectives and for the hypotheses on which its theories and reconstructions are based: from physical chemistry to oceanography, from zoology to volcanology, from geochemistry to applied geophysics, and so forth. It is therefore an eminently synthetic science. On the other hand, geology constitutes the foundation of many other branches of science, some of which once formed part of it and subsequently developed to such an extent that they became autonomous disciplines. Examples include geomorphology, volcanology, glaciology, applied geology, and many others.
For the historical and scientific development, in particular, of the three fundamental branches of geology V. PALEONTOLOGIA; STRATIGRAFIA; TETTONICA. Ramiro Fabiani