Fossil fuels – what are they?

The term fossil fuels maybe isn’t the best, since they are not really made out of fossils. In this case, the word only indicates something about 650 million years old. We are talking about organisms, that sunk to the bottom of the ocean or a puddle of mud. In time, they got covered in sediment, which made just the right conditions to start the natural process of anaerobic decomposition. But only the sediment and a lot of time aren’t the only ingredients in this process. We also need high pressure and high temperatures (around 150 °C). These two factors are usually taken care of by the upper layers of the sediment. Another important aspect is the absence of oxygen, which enables the anoxic conditions. Under these conditions, the organic matter changes its chemical decomposition. Depending on the conditions and the amount of organic matter present, the carbon bonds form differently. This defines the characteristics (boiling point, melting point, density, etc.) as well as the form of some fossil fuels.

When we speak about fossil fuels, most of us make the connection to the dinosaurs, since they are such charismatic beasts. However, we really shouldn’t forget about smaller (plants, mammals etc.) and teeny tiny organisms (microorganisms). All of them played an important role (some bigger in size and others in numbers) during the formation of fossil fuels. Organic matter from animals have turned into petroleum and natural gas and the plant organic matter mostly turned to coal.




It started forming in swampy forests. The process is completely natural and starts with dying off of plant matter. This creates the space for new plants to grow and the (usually quite slow) cycle repeats. During the process, the layer of plants is thickening and the ones below it are slowly rotting. At some point during this process, the environment changed. This led to filling up the spaces in the puddle of organic matter with water and dirt. It took away the oxygen, and induced some chemical and physical changes, enabling the coal to form. Depending on the percent of organic matter and the time it spent captured, different kinds of coal form: peat, lignite, bituminous, and anthracite.

Natural gas and oil

The formation of natural gas and oil is very similar. They have both started forming with organic matter (of mostly marine organisms) that drifted to the seafloor. They started to decay and eventually got covered and mixed with sediment. This is how the deposits lost touch with oxygen, the pressure was taken care of with depth and weight of the sediment. The temperature rose because of the high pressure, as well as because of the natural process of thermal breakdown. During this process, the organic matter is slowly being converted into hydrocarbons and these are further broken down into smaller molecules with the natural process called cracking. When talking about natural gas or petroleum, the only difference is the arrangement of the hydrogen and carbon atoms in the chain. When the molecule is lighter in structure, we get the natural gas and when the structure is heavier, we get petroleum. Of course, we have different kinds of oils and natural gases, which depend on how much organic matter is present, conditions in which they formed etc.

When the two form, they highly depend on porosity and permeability of the rock. The porosity tells us how much empty space is contained within the rock. The rock with the highest porosity is pumice but since they only occur close to the volcanoes, we can’t find them near the oil and gas deposits. The most porous rocks, that can be found in this kind of environments are the sandstones, that can be up to 25% porous. Permeability is measured as how much gas and liquid can flow through the rock. After natural gas and oil are formed, they both start to rise towards the Earth’s surface. The first one moves towards lower density and the other towards lower pressure. Their journey ends when they come to a seal or a trap made out of sediment they can’t penetrate.

Status of the fossil fuels

fossil-fuelFossil fuels are referred to non-renewable a non-sustainable source of energy. This is due to the fact that the formation process is very slow. Because of this and the fact that we are burning them quite quickly, the Earth can’t keep up. Another aspect to this is, that all of this energy was stored away for good and for long periods of time. When we started burning them (factories, cars, etc.), we started massively releasing that stored energy. When we started, we had no idea about how this is going to affect all that we know. Now, we can see the effects everywhere and they are causing numerous problems (air pollution, rising temperatures, health problems etc.). Scientists have already started sticking their heads together in order to try and solve the problem. Some projects are already up and running, but it will take a long time before real effects will be visible. In the meantime, we should keep on searching for the alternatives (wind or solar power) and continue doing the small things to help the nature. They do add up and by doing just a little, we are actually doing quite a lot!

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Again I can end this article with the words, that we have brought this on ourselves when we decided to start digging and pulling the fossil fuels out from their cozy, safe places. Most of the population is unfortunately still highly dependent on fossil fuels, but we can see the trends slowly shifting.

What do you think of fossil fuels? Which renewable and sustainable way of getting the energy do you find the most fascinating and why? I would love to hear your opinion so please leave it as a comment below.

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