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 vast field of doctrines that this term initially embraced and long retained, geology gradually narrowed its boundaries, especially during the 19th century, as certain parts broke away to form new branches of science. But the clear and definitive delimitation of the competence of geology, understood in its strictest sense as pure geology, is even more recent.
Presupposing a knowledge of rocks (lithology, petrography) and of fossils (paleontology), geology can therefore be defined as the science that studies first of all the structural characteristics of the Earth's crust (lithosphere), that is, the conditions of development and mutual position (attitude) of rocks of various nature and origin that form the crust itself, and the processes and causes that have led to its present arrangement and that reflect the vicissitudes the Earth has passed through during the immensely long geological ages.
It would nevertheless be impossible to arrive at a reconstruction of these vicissitudes that was not excessively incomplete and often entirely erroneous, relying exclusively on the elements derivable from the nature, distribution and mutual attitude of rock formations.
To achieve this aim, the indispensable documentation can be found only in fossils, that is, in the remains of plant and animal organisms that lived in past times. Such remains, present within sedimentary rocks of all geological ages and often in a state of admirable preservation, make it possible in fact to reconstruct the characteristics and the sequence of vanished faunas and floras and the physical environment in which their life unfolded, also providing elements for representing to ourselves the nature of the phenomena that, in an unceasing succession, have gradually modified the features of our planet.
The studies and investigations that lead, or tend to lead, to the attainment of the objectives just mentioned constitute the essence of geology understood in the strictest and most genuine sense. Thus delimited, geology comprises two fundamental parts: structural geology and historical geology, also designated respectively by the names tectonics and stratigraphy.
The first deals with the highly varied ways in which rocks are arranged in the complex edifice of the lithosphere, establishing their most characteristic types, with reference to the three categories into which, on the basis of genesis, rocks are grouped, namely 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, 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, besides the basic ones, petrography and paleontology, from which geology does not draw some assistance for its objectives, for the hypotheses on which its theories and its reconstructions are founded: from chemical physics to oceanography, from zoology to volcanology, from geochemistry to applied geophysics, etc. 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 later developed to such a degree as to form autonomous entities. For example, geomorphology, volcanology, glaciology, applied geology and many others.
For the historical-scientific development in particular of the three fundamental parts of geology, v. PALEONTOLOGIA; STRATIGRAFIA; TETTONICA.
Ramiro Fabiani