33: Fossil Fuels- what happens to a fern 300 million years after it dies?

Fossil fuels eh? Awful! Scourge of humanity! But… what are they? And why are they so bad? Should we stop using them straight away? And what does a fern have to do with any of this? As always the answers aren’t always simple, but some of them are quite interesting. This week we will be taking a look at how fossil fuels form, what they are used for, and why various places may or may not want to stop using them asap. Our story begins many many millions of years ago…


As it turns out there is logic in the name, fossil fuels are kind of made from fossils. It all starts when during the time of the dinosaurs and before, in the carboniferous period (260-380 million years ago), something dies. The plant or animal, often microscopic, will lay down on the ground but because of certain environmental conditions like a lack of oxygen, which is needed for decomposers, it won’t fully break down and so will retain some of the energy in its body that it gained through its life. If it is in water, like a slow moving river, lake, swamp or the sea, the dead creature will start to get covered in sediment, little pieces of sand or silt formed by weathering from wind or water erosion. This build-up of sediment can happen on land too, though most often happens in water.

Over time as more and more sediment builds up, the dead organic material of the animal or plant gets buried, and as the sediment gets deeper still, it’s weight starts to compress and compact everything underneath it. This happens over a very long period of time, and with the addition of heat from the earth the bottom layers of sediment where our organic material is can get so compressed that it becomes sedimentary rock. This then goes on to form two main kinds of fossil fuels.

(Image: Timmeko/Flickr/CC BY-SA 2.0)


The first is coal which is formed when the pressure of all this sediment turns the organic material, usually woody plants, into peat. This contains some energy. However, if this peat gets buried even further, the pressure and heat turns it into coal. This contains more energy than peat, and the more pressurised the coal is, the more energy it contains, meaning you can have coal of different qualities. The formation of coal depends on areas having the right environmental conditions for silt to form and for plants to grow, conditions which don’t remain constant throughout history, so you usually just get a layer of coal which formed in suitable conditions sandwiched between two rock layers where historically conditions weren’t suitable. This coal layer is known as a coal seam, and when people are mining for coal they will usually explore to find a seam and then follow this layer horizontally to extract everything along it.

Coal can be burned for energy, and in 2017 was responsible for around a quarter of the world’s energy production.

The black layer is a coal seam in the rock. (Picture:alex.ch/Wikimedia Commons/CC BY-SA 2.0)

Crude Oil and Natural Gas

The other fossil fuel that can form is petroleum. This is made when the organic material is microscopic animals that lived in the seas millions of years ago. With all the pressure of sediments building up, they actually become sedimentary rock. Then over more time and with more pressure (we are talking about A LOT of pressure here) these rocks gets squeezed so tightly they become petroleum, a bit like oil being squeezed out of nuts.

Petroleum has two main natural forms. When conditions are extra high pressurised and hot, petroleum exists in the form of natural gas, a pocket of colourless gas that often sits above the oil products in rock. This gas can come in forms like propane and butane which can be burned for energy, so if you have gas heating or cookers in your house, this is what is being used.

Alternatively, the petroleum may be in the form of crude oil. To access this, holes are drilled into the ground where there is known to be a pocket of oil in the rock, and then it is extracted. After this the crude oil goes through a process called fractional distillation where it is separated out into useful products. This includes gasoline (petrol), kerosene (widely used as airplane fuel), asphalt (used mostly to make roads), paraffin wax (used in many candles, polishes and cosmetics), and plastics (used in like… everything).

Diagram showing oil wells extracting natural gas an oil from the ground on the left, and fractional distillation of the crude oil on the right. When oil and gas are in pockets under the sea they are extracted using oil rigs

Why they’re a problem

If you’ve watched any news lately or have literally any interest in the environment, you’ll have heard a lot of people say how awful fossil fuels are. Why is this?

The first reason is that fossil fuels are a major source of energy. In 2017 coal made up around 25%, natural gas around 20% and oil around 35% of the worlds energy sources. So burning fossil fuels produced up 80% of the entire globe’s energy. To keep producing this amount of energy, and in fact more as the global energy requirements are rising, you need a looooot of fossil fuels. However, they are seen as a finite resource, meaning there is only so much of them and they will run out eventually. This isn’t entirely true, they do renew themselves but it’s over the time span of millions of years which is far too slow for the rate we’re using them, so practically speaking they are finite. This means that if we keep using them at the rate that we are, one day we will run out and suddenly be stuck without a source of energy in most places. How much fossil fuels we have left on earth and so how much time we can still use them for is debated, but that they will run out one day is fact.

For this reason it makes sense not to be so reliant on one source of finite energy, but to have many different sources that can continue to be used when the fossil fuels are gone. The most popular alternative sources are nuclear energy, hydro power, wind power, solar power, geothermal energy and the burning of bio-fuels and waste. These are all renewable sources i.e they won’t run out (though this is debatable for nuclear energy), and all have their positives and negatives too, but are important alternatives to develop and promote if we want to keep having things like heating, functioning hospitals and the internet.

Aside from the need to cleverly plan for the future, the other issue with fossils fuels, perhaps more discussed, is their environmental impact. You get energy out of fossil fuels by burning them. However, when this burning happens you also release a lot of gases. This includes greenhouse gases like carbon dioxide, methane, nitrous oxide and ozone, as well as other air pollutants like nitrogen oxides, sulphur dioxide, volatile organic compounds and heavy metals.

Greenhouse gases, when accumulating in the earth’s atmosphere at higher than natural levels, act as a sort of blanket insulating the world and causing it to warm up, like a greenhouse. This has all kinds of environmental consequences which I won’t go into here (perhaps in a later plog) but safe to say more fossils fuels burned means more gases released means more warming and so more problems. As for the air pollutants, they can be toxic either in the air if they are in too high doses, affecting anything that breathes them, or if they fall down into the soil affecting things that grow there.

World energy usage broken down by source and by area. Data from EnerData

So…. stop using all the fossil fuels now?

It seems quite obvious that stopping our use of fossil fuels as soon as possible would be a clever idea. This is definitely true, and definitely something we should aim for, but realistically not something that will happening overnight. Putting aside cynical thoughts of how fossil fuel companies fund politics to protect themselves from being banned, and make a lot of money for themselves and others so are tricky to oust, they do still have an important role. We should try to shift towards other sources of energy as quickly as possible, but until we have those other sources sorted our energy needs still have to be met somehow.

Also for many less economically developed countries, using fossil fuels may be the only affordable way to make energy. Most economically developed countries went through a period of burning all the fossil fuels, making lots of money, and are now in a better financial position to invest in alternative energies. Telling less economically developed countries that they can’t do this might be seen as a bit unfair, as it may mean they are stuck in poverty and without sufficient energy because they can’t afford it. That’s a tricky debate and discussion for sure, though in good news many great people and projects are working to find low cost ways to use renewable energy, from using reflective metal sheeting to concentrate the sun’s rays onto a kettle to boil water (rather than expensive solar panels), to homemade windmills for powering light bulbs and TVs during the evenings.

There is also a need to make the transition from fossil fuels to more renewable energy in a clever way. Fossil fuel industries are huge employers, so mass closures of industries such as coal mining in areas where it was a major livelihood has caused huge financial difficulties for the people who lost their jobs. If fossil fuel industries are going to reduce in size, there needs to be programmes in place to retrain and find alternative jobs for the people who are losing their jobs.

Simple and cheap ways to use renewable energy do exist. For example these solar cookers simply reflect the sun’s energy to a pot allowing food to be cooked or water to be boiled. (Picture: Brinerustle/Wikimedia Commons/ CC BY-SA 3.0)

With those caveats in place however, moving towards a global energy market that is far less reliant on fossil fuels, and doing this quickly, is important both for the health of the environment and so that we don’t stumble into any tricky situations in the future where our very energy dependent societies suddenly run out of fuel. Who’d have thought that the future of humanity would rely on whether or not we decide to set fire to a multi-million year old shrub!

For more info:

An article about how different products can be extracted from petroleum through fractional distillation (keep clicking the next button for more info): https://science.howstuffworks.com/environmental/energy/oil-refining2.htm

A nice brief summary of fossil fuels:

Music: kongano.com

Title Image: Wikimedia Commons/Public Domain

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