Fossil Fuels – What Are They?

fossil fuels formation diagram
Formation of fossil fuels: oil and natural gas

The world as we know it today would not have existed without fossil fuels. They made the industrial revolution possible in the 19th century. Fossils fuels drive today’s economic growth but also contribute significantly to man-made climate change. They originated from forests and microorganisms that existed in earlier geological ages.

The origin of the term is Latin fossilis, meaning ‘dug up’. The history of fuel technology goes back to the Paleolithic. Fossil fuels have been used since humans made use of fire around 750,000 years ago. Initially, humans used dried plants, wood and peat as raw materials. Later we developed fossil fuels such as oil, coal and natural gas. Today we also have a variety of refined and synthetic materials. Some of these materials have energy potential which is higher than that of natural raw materials. However, fossil fuels still play a major role.

Types of fossil fuels and their origin

Fossil fuels are decomposition products of organic, mainly vegetable matter. They consist of high-energy substances.

In short, fossil fuels are the byproduct of four factors:

  1. Organic matter
  2. Temperature
  3. Time
  4. Pressure conditions

The following fossil fuels exist in nature:

  • Petroleum (oil)
  • Natural gas
  • Coal
  • Lignite (brown coal)
  • Peat

Fossil fuels are also called fossil energy sources. Fossil fuels are not a renewable resource. Their creation process took millions of years. This means that these fuels are not renewable in terms of human time dimensions. At some point all deposits will be used up. Especially since the industrial revolution and due to the diverse uses of these fuels, the deposits have been drastically reduced. If renewability is used as a definition criterion, uranium can also be considered as fossil energy source.


The raw material for fossil fuels of this type is plankton, which floated in the seas millions of years ago. The remains of these tiny sea creatures sank to the bottom and were buried airtight under other layers of sediment, such as sand and clay. The remains decomposed and became digested sludge. Further sediments were deposited above, the weight of which pressed onto the digested sludge. Under this pressure, the temperature rose and the decomposed sludge chemically changed to a mixture of gaseous and liquid hydrocarbons: petroleum. Because it was lighter than water and the surrounding rock, it continued to rise through pores until it encountered an impermeable layer under which the viscous mass collected: an oil deposit had been created.

Natural gas

This material was formed under conditions similar to petroleum. Therefore, both fossil fuels are often found in the same deposit. Natural gas is lighter, which is why it is stored above oil. Natural gas is a gas mixture, the main component of which is methane. The other substances vary depending on the site. It is important to note here that the mixture is non-toxic, flammable and colorless and odorless.

Coal, lignite, peat

These fossil fuels owe their origin to the remains of dead swamp plants. These formed increasingly thick layers of peat over which sediments accumulated. Under their weight, water, oxygen and other gases were pressed out of the peat layer, and the proportion of carbon increased. For thousands of years, the peat turned into brown coal. If the sediment cover and the pressure continued to grow, lignite became black or hard coal. In order to be able to use their stored energy, coal deposits – also known as coal seams – are mined in mines.

Uses of fossil fuels

Fossil fuels are still indispensable raw materials for the three areas of the energy industry:

  • Heating and heat generation
  • Power generation
  • Fuels for transportation and traffic

Source: Our World in Data – Energy

Heat generation

The combustion of fossil fuels generates heat for heating residential and commercial properties in central heating systems, boilers and individual fireplaces. The use of primary energy can be significantly minimized through insulation and the use of efficient technology. Coal and natural gas are also used to generate heat for energy-intensive industries such as the steel industry.

Power generation

Electricity generation in power plants generates heat from fossil fuels. This is used to operate steam turbines and generators. By means of combined heat and power, part of the waste heat generated can be used. This significantly increases the overall efficiency. Electricity generation and heat generation can also be combined efficiently with fuel cells.

Fossil fuels as the basis for fuels

Petroleum is the basis for the following fuels: petrol and diesel, kerosene as high-performance fuel, especially in aviation, marine diesel and the low-quality heavy oil for marine engines. Alternatives such as synthetic liquid fuels from natural gas are becoming increasingly important in the automotive sector.



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