لخّصلي

Definition.

Definition. Subjects (topics, themes) of geology
The word geology comes from the Greek "gê" (=earth) and "logos" (=discourse, science).
Geology is a science concerned with the study of the Earth (or globe), the planet of the solar system. It is also
interested in other planets and stars, the best known of which are the Moon and Mars.
Geology is primarily concerned with the study of the materials (rocks) that make up the Earth's crust. The
Earth's crust is the outermost layer of the Earth, directly accessible to observation.
Like biology, geology is a natural science. To carry out their studies, geologists need a range of tools, from
observation with the naked eye or macroscopic observation, to satellite observation, using a hammer, a
magnifying glass, a compass and topographical maps.
2. Aims of geology
Geology, in the broadest sense of the term, is concerned with the study of rocks, minerals and fossils, as well
as the natural resources contained within and on the surface of the Earth.
Geology is also concerned with terrestrial activity, illustrated by earthquakes, volcanic eruptions, etc.
a. Scientific goals: The aim is to reconstruct the history of the formation and evolution of the
Earth's surface. The Earth's surface is constantly changing. Current research shows that 5 billion years ago,
the Earth's surface consisted of molten substances (magmas). Their high temperature gradually decreased,
which initially allowed various gases (carbon dioxide, oxygen and others) to develop.
Living organisms, algae and then animals, appeared. The first appeared 3 billion years ago, the second 600
million years ago.
We also know that the continents have changed position and that the climate, animals and vegetation have
changed over time. Some of these phenomena can be seen in the fossil traces (imprints of past life)
contained in rocks.
Geology provides us with information about the Earth's past.
b. Economic goals: Geology also has a practical goal. The deep layers are explored with the aim of
discovering mineral resources (water, coal, ores, hydrocarbons, etc.).
3. The main disciplines (or specialities)
Geology covers a wide range of subjects. For this reason, there are different specialities.a. Petrography and petrology Petrography is the study of rocks and aims to describe rocks and
their classification. Microscopic study (polarising microscope) completes the macroscopic study.
Petrology: this is not the study of oil (when it is, it is called petroleum geology), but the study of rocks based
on geochemistry (rock chemistry).
b. Mineralogy and crystallography: Mineralogy is concerned with minerals (their chemistry, e.g.
quartz; SiO2), crystallography with the study of crystals.
c. Sedimentology: The aim of sedimentology is to identify the mechanisms by which sedimentary
rocks are formed. A sedimentary rock is formed by the accumulation of debris from other rocks.
d. Stratigraphy This is the study of geological strata (or layers). It involves tracing the succession
and age of the different layers.
f. Paleontology: This is the science of fossils, i.e. animals and plants that have disappeared but
whose traces are preserved in rocks. A fossil is a remnant, a trace, of an animal or plant.
h. Marine geology or geological oceanography: study of the seabed for offshore oil exploration,
characterisation of the environment for coastal protection and development.
i. Tectonics or structural geology: This studies the deformation of geological formations. It shows
that rocks (magmatic, metamorphic and sedimentary) break and fold during or after their formation.