What is Geology?

Geology is Science!

Sure, but what sort of fields and concentration-areas exist within this science of the earth?

What You'll Learn to Do

  • Describe "geology" and identify some of its main principles.
  • Identify the main branches of geology.

The Science of Geology

To some degree geology is quite familiar, it's all around us!

The magnificent rock formations in Yosemite, California (see Figure 1), have a story.  The have this appearance because of geology (in a nutshell, the story of Yosemite goes like this--magma that cooled beneath the surface during the age of dinosaurs and then brought upwards by mountain uplift, and finally carved by glaciers!).

One objective of geology is to study the processes that create and modify landforms.

A panoramic shot of half dome and the rock formations that surround it. The massive formations curve and rise as mountains. Figure 1. Half dome in Yosemite, National Park, California, USA

Drive across the U.S., or look out the window of an airplane, or just simply go outside--

if you wonder how the world came to look the way it does, you're asking an important geological question.

Alan Lester, Geologist and Airline Pilot

There are other aspects of geology where the focus involves materials and processes that are not so visible.  Just a few examples might be:

  1. What is earth's interior like?
  2. Why does our planet have a magnetic field?
  3. A microscopic close-up of Yosemite granite would show several different mineral types.  Why are there different minerals?  What are these minerals made of?
  4. What creates mountains, or oceans, or deserts; and why do they come and go over enormous time spans?
  5. Can we apply our knowledge of the earth to other planets?

Earth as seen from Apollo 17 Figure 2. The "Blue Marble"

What is Geology?

In its broadest sense, geology is the study of Earth—its exterior surface, its interior, and the materials and processes that shape it.  It evaluates the world in four dimensions, such that the planet is viewed as a whole, and through time.

Geology is a science: we use deductive reasoning and scientific methods to understand geological problems.

Geology is arguably one of the more integrated of all sciences because it involves the understanding and application of so many disciplines: physics, chemistry, biology, mathematics, astronomy, and others. Like some of the other sciences, geology addresses extra dimension of time—billions of years of it. Geologists study the evidence that they see around them, but in most cases, they are observing the results of processes that happened thousands, millions, and even billions of years in the past. Those were processes that took place at incredibly slow rates—millimeters per year to centimeters per year—but because of the amount of time available, they produced massive results.

A mountain with a glacier between it and another mountain range. Figure 3. Rearguard Mountain and Robson Glacier in the Rocky Mountains of British Columbia

Mountain uplift is an example of a process that typically occurs in the range of millimeters per year, yet over time can yield spectacular results (even on a planet where gravity and erosive forces work against it!).

The peak on the right is Rearguard Mountain (Figure 3), which is a few kilometers northeast of Mount Robson, the tallest peak in the Canadian Rockies (3,954 m). The large glacier in the middle of the photo is the Robson Glacier. The river flowing from Robson Glacier drains into Berg Lake in the bottom right.

The sedimentary rock layers, of which these mountains are made, formed in ocean water over 500 million years ago. A few hundred million years later, these beds were pushed east for tens to hundreds of kilometers by tectonic plate convergence and also pushed up to thousands of meters above sea level. Over the past two million years this area—like most of the rest of Canada—has been repeatedly glaciated, and the erosional effects of those glaciations are obvious. The Robson Glacier is now only a small remnant of its size during the Little Ice Age of the fifteenth to eighteenth centuries, as shown by the distinctive line on the slope on the left. Like almost all other glaciers in the world, it is now receding even more rapidly because of human-caused climate change.

Geology is also about understanding the evolution of life on Earth; about discovering resources such as metals and energy; about recognizing and minimizing the environmental implications of our use of those resources; and about learning how to mitigate the hazards related to earthquakes, volcanic eruptions, and slope failures. All of these aspects of geology, and many more, are covered in this course.

The Branches of Geology

Numerous branches of geology exist.  You will NOT be required to know all the different types of geologists, by name, but it is important to see the wide variety that exists!

Some examples:

A mineralogist studies minerals-- analyzing both composition and atomic structures.

A seismologist evaluates how seismic waves pass through the earth.  (Figure 4).

A two part figure. Part A: A glass display case of several types of minerals. Part B: A seismograph. A paper roll inset in a device that records the strength of earthquakes. Figure 4. (A) Mineralogists focus on all kinds of minerals. (B) Seismographs are used to measure earthquakes and pinpoint their origins.

A mountain with distinct layers in a chevron panel Figure 5. These folded rock layers have bent over time. Studying rock layers helps scientists to explain these layers and the geologic history of the area.-- Studied by Structural Geologists

Volcanologists, as one might guess, study volcanoes!  A volcanologist is really one branch of Igneous Petrology.  Petrology is not the study of petroleum, but instead the study of rocks (petro or petra,  from Greek meaning rock).

Petroleum geologists are concerned with the origin and location of hydrocarbon resources  (oleum, referring to oil, from Greek).

Scientists who compare the geology of other planets to Earth are planetary geologists (or lunar geologists, in the case of our moon).

A geochronologist works on determining rock ages can tell how old rocks are and determine how different rock layers formed (Figure 5).

Hydrologists study rivers and lakes, the underground water found between soil and rock particles, or even water that is frozen in glaciers. The list goes on and on!

As opposed to specific individuals, geology can also be subdivided into "branches" with some examples as follows:


Geochemistry is the study of the chemical processes which form and shape the Earth. It includes the study of the cycles of matter and energy which transport the Earth's chemical components and the interaction of these cycles with the hydrosphere and the atmosphere.

It is a subfield of inorganic chemistry, which is concerned with the properties of all the elements in the periodic table and their compounds. Inorganic chemistry investigates the characteristics of substances that are not organic, such as nonliving matter and minerals found in the Earth's crust.


Oceanography is the study of the composition and motion of the water column and the processes which are responsible for that motion. The principal oceanographic processes influencing continental shelf waters include waves and tides as well as wind-driven and other oceanic currents. Understanding the oceanography of shelf waters and the influence this has on seabed dynamics, contributes to a wide range of activities such as the following:

  • assessment of offshore petroleum production infrastructure
  • seabed mapping and characterisation for environmental management
  • marine biodiversity surrogacy research
  • assessment of renewable energy potential


Paleontologists are interested in fossils and how ancient organisms lived. Paleontology is the study of fossils and what they reveal about the history of our planet. In marine environments, microfossils collected within in layers of sediment cores provide a rich source of information about the environmental history of an area.


Sedimentology is the study of sediment grains in marine and other deposits, with a focus on physical properties and the processes which form a deposit. Deposition is a geological process where geological material is added to a landform. Key physical properties of interest include:

  • the size and shape of sediment grains
  • the degree of sorting of a deposit
  • the composition of grains within a deposit
  • sedimentary structures.

These properties together provide a record of the mechanisms active during sediment transportation and deposition which allows the interpretation of the environmental conditions that produced a sediment deposit, either in modern settings or in the geological record.


Involves the investigation of the solid earth, via application of electromagnetic, gravity, magnetic, and seismic studies!

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