A fossil fuel is a hydrocarbon-containing material formed naturally in the earth’s crust from the remains of dead plants and animals that is extracted and burned as a fuel.
The main fossil fuels are coal, crude oil and natural gas.
Fossil fuels may be burned to provide heat for use directly, such as for cooking or heating, to power engines or to generate electricity.
Some fossil fuels are refined into derivatives such as kerosene, gasoline and propane before burning.
The origin of fossil fuels is the anaerobic decomposition of buried dead organisms, containing organic molecules created by photosynthesis.
The conversion from these materials to high-carbon fossil fuels typically require a geological process of millions of years.
The main fossil fuels: gas, oil and coal.
In 2019, 84% of primary energy consumption in the world and 64% of its electricity was from fossil fuels.
The large-scale burning of fossil fuels causes serious environmental damage, and over 80% of the carbon dioxide (CO2) generated by human activity is from burning them.
Around 35 billion tons a year, compared to 4 billion from land use change.
It is mostly absorbed by the ocean, but can only remove a small part of this, therefore there is a net increase of many billion tons of atmospheric carbon dioxide per year.
The burning of fossil fuels is the main source of greenhouse gas emissions causing global warming and ocean acidification.
Most air pollution deaths are due to fossil fuel particulates and noxious gases.
It is estimated that this costs over 3% of global GDP  and that fossil fuel phase-out would save millions of lives each year.
Petroleum and natural gas formed as a result of anaerobic decomposition of
aquatic phytoplankton and zooplankton that died and sedimented in large quantities under anoxic conditions millions of years ago.
Over millions of years of geological time this organic matter, mixed with mud, became buried under layers of inorganic sediment.
High temperature and pressure caused the organic matter to chemically alter, into a waxy material known as kerogen, which is found in oil shales.
Subsequently , and with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis.
The energy released in combustion is still photosynthetic in origin.
Terrestrial plants tended to form coal and methane.
Terrestrial plants also form type III kerogen, a source of natural gas.
Although fossil fuels are continually formed by natural processes, they are classified as non-renewable resources because they take millions of years to form and known viable reserves are being depleted much faster than new ones are generated.
Fossil fuels have been important to human development because they can be readily burned to produce heat.
Natural gas, once flared-off as an unneeded byproduct of petroleum production, is now considered a very valuable resource.
Natural gas deposits are also the main source of helium.
Heavy crude oil is much more viscous than conventional crude oil.
Oil shale and similar materials are sedimentary rocks containing kerogen.
Kerogen is a complex mixture of high-molecular weight organic compounds, which yield synthetic crude oil when heated.
The development of synthetic nitrogen fertilizer has significantly supported global population growth, and it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use: 50% of the world’s food relies on fertilizers.
The burning of fossil fuels has a number of negatives: harmful environmental impacts where the effects extend beyond the people using the fuel.
All fossil fuels release CO2 when they burn, thus accelerating climate change.
Burning coal, and to a lesser extent oil and its derivatives, contribute to atmospheric particulate matter, smog and acid rain.
In 2020, renewables overtook fossil fuels as the European Union’s main source of electricity for the first time.
Climate change is largely driven by the release of greenhouse gasses like CO2, with the burning of fossil fuels being the main source of these emissions.
Climate change is negatively impacting ecosystems, including contributing to the extinction of species and reducing people’s ability to produce food, thus adding to the problem of world hunger.
World Health Organization having stated climate change is the greatest threat to human health in the 21st century.
Combustion of fossil fuels generates sulfuric and nitric acids, resulting in acid rain, impacting both natural areas and the built environment.
Fossil fuels also contain radioactive materials, mainly uranium and thorium, which are released into the atmosphere.
In 2000, about 12,000 tons of thorium and 5,000 tons of uranium were released worldwide from burning coal.
Burning coal also generates large amounts of bottom ash and fly ash.
Harvesting, processing, and distribution of fossil fuels also have environmental effects.
Coal mining methods, particularly mountaintop removal and strip mining, have negative environmental impacts, and offshore oil drilling poses a hazard to aquatic organisms.
Fossil fuel wells can contribute to methane release via fugitive gas emissions.
Oil refineries also have negative environmental impacts, including air and water pollution.
Coal is sometimes transported by diesel-powered locomotives, while crude oil is typically transported by tanker ships, requiring the combustion of additional fossil fuels.
Environmental pollution from fossil fuels impacts humans because particulates and other air pollution from fossil fuel combustion cause illness and death when inhaled: premature death, acute respiratory illness, aggravated asthma, chronic bronchitis and decreased lung function.
Global air pollution deaths due to fossil fuels in 2018 have been estimated at over 8 million people, nearly 1 in 5 deaths worldwide.
Fossil fuels cause the highest levels of greenhouse gas emissions and are the most dangerous for human health.
Modern renewable energy sources appear to be safer for human health and cleaner.
European data suggests death rate from accidents and air pollution are as follows per terawatt-hour: coal (24.6 deaths), oil (18.4 deaths), natural gas (2.8 deaths), biomass (4.6 deaths), hydropower (0.02 deaths), nuclear energy (0.07 deaths), wind (0.04 deaths), and solar (0.02 deaths).
The greenhouse gas emissions from each energy source: coal (820 tonnes) oil (720 tonnes), natural gas (490 tonnes), biomass (78-230 tonnes), hydropower (34 tonnes), nuclear energy (3 tonnes), wind (4 tonnes), and solar (5 tonnes).
Coal, oil, natural gas, and biomass cause higher death rates and higher levels of greenhouse gas emissions than hydropower, nuclear energy, wind, and solar power.
It is proposed that 1.8 million lives have been saved by replacing fossil fuel sources with nuclear power.
Air pollution from fossil fuels in 2018 has been estimated to cost US$2.9 trillion, or 3.3% of global GDP.