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What is Geology?

Everything we know about the Earth's history comes from geology, but what is geology?

Well this post is everything you need to know about geology and what we can learn from it! Some confusion seems to exist between what the difference is between geology, paleontology and even archeology and what they actually are?

Well, let's address that now! I have explained paleontology in a previous post, and archeology is – while you're still digging up old things – the study of human history and artefacts (so anthropology is where the two overlap).

Geology, however, is a subject considered much broader and is more of an umbrella term that includes paleontology. The short answer: geology is the study of Earth's natural history and its processes through the main medium of rocks.

Seems pretty contained right? Well, when you start thinking about it, the amount this entails is staggering! There is a lot of things within the planet, so an easier way of explaining what geology is, is to go through the main disciplines that geology entails. Before we start, let me just go over the three basic rock types in geology so we can have a better understanding of what geology is.

diagram showing the rock cycle.

Here is one you may or may not remember from school: the rock cycle. The rock cycle shows the basic lifecycle of a rock as it constantly transitioned between igneous rocks, metamorphic rocks and sedimentary rocks. There isn't really a beginning or an end to this cycle and it can skip a step or two, but let's start with igneous rocks.

What are igneous rocks?

Igneous rocks are raw, cooled down lava (liquid rock above the surface) or magma (liquid rock below the surface). Igneous rocks are usually formed beneath the Earth's surface before being exhumed (pushed up to the surface). You can get various types of igneous rock, depending what chemicals were in the lava/magma and what conditions it cooled down under. As a general rule of thumb, the bigger the crystals, the slower the magma took to solidify. This is why cooled down lava that solidified very quickly (e.g. after a volcanic eruption) becomes glass (e.g. obsidian).

Now the rock can go one of three ways: it can either be pushed back down to re-melt, it can be exposed to high temperatures and/or pressure to become a metamorphic rock, or it can be eroded away with the granules being carried off to form sedimentary rocks.

What are metamorphic rocks?

If it becomes a metamorphic rock, this means that it was pushed down beneath the surface deep enough to expose it to tremendously high pressures and temperatures (but not enough to melt it). While the rocks stay as a solid, they do change from the temperature and pressure, usually forming new minerals. The type of metamorphic rock will depend on the source rock and whether the change was from heat, pressure or both (as well as how much it was exposed to). From here the metamorphic rock can remain as it is, be eroded to become a sedimentary rock, or melted down again to become an igneous rock.

What are sedimentary rocks?

Sedimentary rocks are bits of other rocks and minerals that have eroded away and, over millions of years, squashed together gently to cement together and form the rock. This is the most common type of rock that you'll see, making up 70% of the Earth's surface. Sedimentary rocks are the best at recording everything that is happening on the Earth's surface, such as preserving proxies for paleoclimate and, as the only rock gentle enough to preserve fossils, life. From here the sedimentary rock can either re-erode to form another sedimentary rock, or be pushed back down below the surface to either become a metamorphic rock or down enough that it melts back into magma.

Those are the basics, but it is a subject I'll delve into in a later post! For now, let's take a look at what types of geology there are...


This is the one we all know and love! I have explained in full what paleontology is before, but in short, it is the study of the natural history of life on Earth. There is obviously much overlap with zoological studies, but it is primarily a geological discipline, since fossils are found in sedimentary rocks. In fact, paleontology is part of geology because fossils ARE rocks! Want to know more? There'll be a post coming soon!


As the name suggests, sedimentology is the study of sedimentary rocks. A sedimentologist can tell a lot about what the world was like on the surface millions of years ago. They can tell what the atmospheric and temperature conditions were, what way the wind often blew, the migration patterns of a river, whether the area was land or deep ocean, or even local and global disasters that happened!

Igneous/metamorphic petrology

These types of petrology look mainly at how igneous and metamorphic rocks formed. It is thanks to petrology that we know what the inside of the Earth is made out of, since certain minerals form only when certain elements are present. Igneous petrology in particular looks a lot at volcanoes and how they are formed (there are a few types of volcano) and metamorphic petrology focuses on what the conditions are below the surface.

Structural geology

Structural geology is a discipline that looks primarily into how rock structures form as well as the effects that formation can have. Ever wondered how mountains are formed? Or what causes earthquakes? Or even how the continents have been able to move? It is all caused by the movements we see on the giant rock conveyor belt that is Earth. These movements can shift, bend and break rocks at both a microscopic and continent size level!


If geology was an office, geophysicists would be the IT department. This is where most of the main expensive toys are, as geophysics studies all sorts of things, from deep pressure formed by gravity to seismology, which looks into how energy waves behave within rocks. It is thanks to geophysics that we know that the core is liquid without having to dig all the way down there! It is also thanks to geophysics and structural geology working in tandem that we can predict earthquakes (to a very approximate degree).


If so much of geology looks at the past and present, climatologists are the ones who can tell the future. Using a variety of signs known as proxies, climatology tells us the chemical composition and temperature of a given environment as well as potential causes for it. From this information, we can project how things are going for our future and the future of the planet, as well as what we can do to change it.

Now, I have obviously skimmed over A LOT of information, as well as other facets of geology, but those are the basics of what geology is and just how much it can actually tell us.

Feel something was missed that you'd like to know more about? Be sure to comment down below and let me know!

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