Fossil fuels

Summary: Fossil fuels play a major role in providing the world’s energy supply. Fossil fuels are mineral fuels formed from the fossilized remains of dead plants and animals, compressed and heated over hundreds of millions of years, and are found within the top layer of the earth’s crust.

There are three types of fossil fuels: coal, petroleum (or oil), and natural gas. These energy sources are extremely important, because they are used in generating the majority of the world’s electricity supply and providing transportation fuels. Sometimes referred to as mineral fuels, fossil fuels are generally thought of as nonrenewable energy sources, because they have been formed over hundreds of millions of years through the process of decomposition of prehistoric plants and animals—thus accounting for their being called fossil fuels. There is a limited quantity of fossil fuels available in the world.

Most people think that dinosaur remains have created the fossil fuels that are used today, but in fact most of the fossil fuels found today were formed millions of years before the first dinosaurs. These living things that died hundreds of millions of years ago began to decompose and over time were buried under thousands of feet of rock, sand, and mud successively layering on top of the decomposing organic matter. Over time, this matter was exposed to heat and pressure from Earth’s crust and became fossilized, forming the fossil fuels known and used today. The time it took to form the different types of fossil fuels depended on the combination of different kinds of animal and plant materials that were present and the environmental conditions, such as temperature and pressure, to which they were subjected while they were decomposing.

Some decomposing materials were once covered by water formations that eventually dried up, leaving additional sediments from the preexisting oceans or lakes. After these waters receded, the combination of heat, pressure, and bacteria began the process of compacting and compressing these organisms under layer upon layer of silt. Oil and natural gas began to form in many of these areas as a thick liquid which, buried at greater depths underground, began to “cook” under heat and pressure. It is in places where large, dense rock formations blocked the eventual seeping up to the surface of these liquids or gases that many of the oil and natural gas reserves being mined today have been found, hidden under these so-called caprocks. Coal has been formed through a similar process, also taking place over hundreds of millions of years, although the primary ingredient for coal is the accumulation of partially decayed and decomposing trees and land plants such as ferns. Over time, the organic material began to decompose, and with increased pressure and high temperatures, the layers of sediment become solidified into rocky material.

Coal

Coal is believed to have been used since some 3,000 years ago by the Chinese to smelt copper in northeastern China. It was later used by the Romans for heating, and around the beginning of the 1700s the English began using coal in place of charcoal wood once they discovered that coal burns more cleanly and produces more heat. When the steam engine was invented in the 1800s, it was designed to run on steam produced by burning coal, and with the rise of the Industrial Revolution, huge amounts of coal were extracted to power the boilers for steam-driven ships and trains. Fueled by coal, these modes of transport became commonplace. Today, coal still supplies a significant share of the world’s energy demand, although some nations have sought to reduce its use due to its polluting qualities.

Of all the fossil fuels, coal is the most abundant, especially in the United States, which has an estimated quarter of all global coal reserves. The United States is one of the largest exporters of coal in the world. Coal predominantly consists of carbon and its energy content can range anywhere from 5,000 to 15,000 British thermal units (Btu) per pound. Four types of coal, sometimes referred to as “ranks,” are mined today:

Lignite, with the lowest energy content of the four types, is also the most commonly found in the world, characterized by its dark brown, blackish color and its relatively soft texture, sometimes exhibiting the original wood form.

Subbituminous coal, which ranks just above lignite, is slightly more potent as a source of energy when burned and is characterized by its dull black color.

Bituminous coal, which produces more energy than the previous two types, is sometimes referred to as “soft” coal.

Anthracite coal, which gives off the most energy of all the four ranks, is also the rarest and hardest type of all.

Coal is used for electricity generation and as a heating fuel in industrial and manufacturing industries, particularly for the production of steel. Burning coal releases toxins such as mercury, barium, zinc, lead, chromium, arsenic, nickel, ammonia, and hydrochloric acids into the atmosphere. The by-products of coal, in addition to the heat generated through burning it, are used in many different products, such as methanol. These components of coal can be isolated and used to make medicines, fibers, plastics, and fertilizers. For instance, steel industries use coal to make coke by cooking it in furnaces; the burning of coke, which gives off extremely high temperatures, is necessary for iron ore to be smelted in order to make steel. The high temperature given off by burning coke is critical in steel production, as it gives steel the needed flexibility and strength for its later uses in construction and manufacturing.

Coal is extracted either by surface mining or by deep underground mining. The process of surface mining is relatively simple, less expensive than deep mining, and takes place in generally flat areas. The extraction process begins with the removal of topsoil and leveling of the surface so that the coal bed is exposed. Once the area is cleared, the coal is dug out and transported from the pit. The removed topsoil is then sometimes replaced in the final land-reclamation stage.

If the coal beds are too deep below the surface or the landscape surrounding them too hilly or mountainous, then underground mining techniques are used. Deep mining was once a dangerous and risky task, but in modern times, with the advent of automated digging, many underground coal mines are highly mechanized. Automated mining has meant that the digging of shafts and tunnels is done by long cutting machines that continuously move along the tunnels to cut and extract the coal. Once loosened or removed from the walls, the coal is lifted to the surface by means of a conveyor, reducing the health and safety risks for workers.

Petroleum

It is believed that the Chinese used petroleum as far back as 2000 BCE to heat their homes and burn in lamps for light. The extraction of crude oil (as petroleum is often called) from coal and shale began in the mid-nineteenth century in earnest, when its value first began to be realized. Since then, the exploration, knowledge, and use of crude oil have developed rapidly, especially with the advent of the automobile in the early twentieth century. This invention, run by an internal combustion engine, demanded gasoline to run its engine, and by the 1950s oil had become one of the most commonly used energy sources all over the world, mostly for transportation.

Oil stores the greatest amount of energy and is more powerful than any other fossil fuel. It is a combination of hydrocarbons, oxygen, nitrogen, and sulfur formed over hundreds of millions of years. In the twentieth century, the world relied heavily on the abundance and relatively cheap cost of oil to fuel global economic development. The majority of petroleum is used to produce gasoline or as a fuel source to be burned in combustion engines, and the transportation and industrial sectors, which account for the majority of energy use in general, especially depend on petroleum and other liquid fuels. Petroleum is also used to produce diesel, heating oil, propane, jet fuel, and petrochemical feedstock (or raw material input) for the manufacture of other chemicals and a broad variety of common products, such as plastics, fertilizers, rubber, washing liquids, and tires.

Oil reserves exist in many parts of the world, but the largest concentrations, and thus biggest oil-producing countries, are in the Middle East, Russia, and North America. Some of the largest producers are the United States, Saudi Arabia, Russia, Canada, China, Iraq, the United Arab Emirates, and Brazil.

Petroleum, or crude oil, is a black or yellow liquid substance found in large quantities underground in areas called reservoirs. Contrary to what most people believe, petroleum does not sit in large pools underground, waiting to be extracted, but as tiny drops found in small spaces or pores that are embedded in rock formations, visible only with the use of a microscope. Oil extraction is an expensive task, as much information is needed about a reservoir before drilling can begin. First, scientists can use sound waves to analyze the types of rocks below ground and whether or not they hold oil. It is important to have a good understanding of the pores in the rocks, how easily and quickly the oil droplets can be moved through these pores, and where spaces in the rock formations are located, so that drilling can be more precisely targeted. Another way of determining if the rocks have oil is to drill a preliminary well and remove some rocks in order to examine them for oil droplets.

Once it is confirmed that a reservoir has the right characteristics to be drilled, a production well is constructed. When the drill first hits the reservoir, the weight of millions of tons of rocks and millions of years of built-up heat and pressure may force some oil quickly up to the surface. This creates what is commonly thought of when people discover oil reservoirs: a fountain of oil that comes spurting up and shoots into the air (although oil producers have installed pressure-control equipment on the wells to prevent this waste from happening).

Petroleum reservoirs also exist deep below the ocean, so offshore platforms are built from which to drill for the oil. These platforms, also known as oil rigs, float off the coast and can vary in size, depending on the characteristics of the targeted reservoir. The platform must hold all the necessary equipment for deep-sea drilling to take place, including pressure-control equipment to prevent oil from gushing up and out into the water when the well is first tapped.

After a well has been drilled, there are two stages of oil production. The first, called primary production, can last from a few days to years. The oil is forced up through the pores in the rocks or in the fractures in the rock formation by pressure that has naturally built up under the surface. Oil flows easily up from the reservoir through the wells in this stage.

After the pressure begins to drop, the secondary stage begins: a process called secondary recovery, which uses an additional well and steam or water to force up the oil remaining in the reservoir. Natural gas can be found alongside oil, and when the petroleum is pumped out, the natural gas can be separated and is sometimes pumped back into the reservoir to increase the pressure and maintain the flow of oil. Tertiary, or enhanced, recovery methods may also be used when it is economical to maximize production with more involved techniques.

The different forms of oil recovery include the following:

• Thermal recovery, a process that uses steam injectors to thin the oil so that it will flow up more easily from the reservoir;

• Gas injections, which increase the pressure in the reservoir to force up the oil and increase the speed at which it flows through the well; and

• Chemical injections, which help to ease the flow of oil droplets along the surface, reducing friction and thereby speeding up the extraction process through the well.

Alternative methods such as horizontal drilling and hydraulic fracturing (fracking) can also be used to improve yields from less traditional petroleum reserves such as shale oil. These techniques became increasingly common in the twenty-first century, greatly changing the global oil industry. However, they generated much controversy for their negative environmental impacts.

Once the petroleum has been extracted from a well, it must be cleaned, transformed, and refined into a form that can be used to produce the fuels and chemicals to be made from it. Impurities such as sulfur, nitrogen, and heavy metals are removed during the refining process, and a distillation process is used to separate the different hydrocarbons, separating the crude oil into liquids and vapors, such as gasoline, based on the boiling points and weights of the various hydrocarbons of which oil is composed. The oil is processed through big furnaces, where the lightest of the components, such as propane, butane, and petrochemicals used to manufacture plastics and fabrics, turn to vapor and easily rise to the top and later condense into liquids. The second-lightest fractions are gasoline, kerosene, and diesel fuel. Finally, the heaviest components, used to make home heating oil or shipping fuel, remain on the bottom. This separation process allows for the creation of the various products and fuels that are petroleum-based. Once refined, the different fuels are distributed via pipelines to additional refineries or storage facilities, from which they can be shipped elsewhere.

Natural Gas

Natural gas is an abundant energy resource, the least carbon-intensive of all the fossil fuels, and it is either released from coal or found mixed with oil. It is easy to transport and use, and the demand for natural gas has been growing steadily since its first use in the early 1800s to light street lamps.

The Greek historian Plutarch was probably the first to “discover” natural gas, as noted in his writings on the “eternal flames” in what is today known as Iraq. Although originally thought to be a useless gas, natural gas wells were drilled by the early nineteenth century, and by the mid-nineteenth century, Robert Bunsen had invented a way to mix natural gas with air and burn it in what came to be known as the Bunsen burner. Natural gas was then used to generate heat for cooking and heating buildings. With the advent of better engineering and technology for metal piping, natural gas distribution and a network of pipelines have rapidly expanded, creating a large market for its use in industrial and commercial heating, electricity generation, and cooking all over the world. Natural gas can also be compressed and used for fuel in transportation.

Natural gas reserves are found all over the world, from Africa and Asia to the United States and Latin America. The majority of reserves are concentrated in the Middle East (Iran, Qatar, Saudi Arabia, and the United Arab Emirates), Europe, and Russia, with some slightly smaller reserves in Asia and the Americas. As of 2022, the United States remained the biggest producer of natural gas, followed by Russia. There are estimates that many large reserves still exist, but despite recent technological advancements, accurately estimating the amount remaining is a challenge.

Natural gas is used in a number of ways. Electricity can be generated with natural gas, and in many countries highly efficient, combined turbine and heat-recovery systems have been developed to produce electricity from both the turbine and a heat and steam generator. Besides its importance as a reliable and efficient energy source, natural gas is used to produce many household goods, such as medicines, fertilizers, plastics, and paint. Propane, used for barbecues and as a household fuel source in rural areas, is yet another example of a product of natural gas. Natural gas is often thought of as smelling like rotten eggs, but actually it is an odorless, colorless gas. The smell is a chemical added by gas companies as a safety measure so that it can be smelled if it is leaking from a pipe.

Natural gas wells are drilled underground to extract the reserves found in porous rock. The difficulty and cost of producing natural gas depend on where it is found, as some reserves require more complex extraction processes. Natural gas reserves are found in shale rock formations, coal seams, and sandstone beds. Fractures in rock formations through which the gas must be forced out can be opened by a process of cracking the rock in order to improve the flow of gas, or fluids can be pumped into the reservoirs to increase the pressure in the well. Methane gas can be found in coal beds and is a potentially valuable source of fuel, despite the risk it poses to miners. Sandstone is yet another source, although extraction from this rock can be especially costly, as the deposits are often trapped in very small pores or holes.

Natural gas production is in some ways similar to oil extraction; in fact, in the process of drilling for oil, natural gas is sometimes also found and can be extracted as well. Just as oil can freely flow to the surface, lightweight natural gas can easily be forced up to the surface, thanks to the pressure trapped in underground reservoirs. However, these easily tapped wells are not very common, and most use a pumping system that functions, similarly to those used in oil extraction, to force out the remaining gas trapped underground. Once natural gas is extracted from the reserves, it is processed so that liquid hydrocarbons, sulfur, carbon dioxide, and other components can be removed and the gas can be sent directly on to end users. Otherwise, the gas is piped to large, underground storage terminals until it is needed.

Liquefied natural gas (LNG) is another natural gas product. After the gas is extracted from the well, it is treated to remove impurities, and then, as the name implies, it is liquefied through a process of cooling and condensing. Once the LNG is made, it can be easily transported by tankers and other ships to where it is needed; after delivery, it is transformed back to its original, gasified state. Then it can be piped and delivered, as a gas, to end users. While the transport and conversion process for LNG is rather complex and can be very expensive, by the early 2020s several countries had increased production and export of LNG, particularly as some companies claimed that it was a "cleaner" alternative to fuels such as coal. Despite many climate experts noting that LNG production and transport still proved highly deleterious to the environment, demand for this gas product had only continued to grow, with Qatar, Australia, and the United States leading the export market for LNG as of 2022.

Environmental Concerns

Although they have become a key part of industrialized society, fossil fuels are often criticized by environmentalists. As nonrenewable resources, they are not considered part of a long-term sustainable development model. Burning fossil fuels also releases pollutants, including atmospheric carbon dioxide. This and other greenhouse gases contribute to global warming and other forms of anthropogenic (human-induced) climate change, regarded by scientists as a key threat to both human society and life as a whole. Other forms of pollution and environmental damage attributed to fossil fuel use include acid rain, particulate air pollution, mountaintop removal from strip mining, and oil spills. Both terrestrial and aquatic ecosystems can be heavily disrupted by fossil fuel prospecting and extraction activity. Due to such concerns, by the 2020s many countries had set goals to transition industries to sustainable, renewable resources such as solar and wind energy or implement technology such as biofuels and carbon capture, with some committing to reaching net-zero emissions. At the same time, all three fossil fuels remained in use to some extent at that point, though often at lower levels than in the past, across the world. Though the first year of the COVID-19 pandemic declared in early 2020 saw a decrease in energy demands and subsequently the use of fossil fuels and carbon emissions as lockdowns and other measures of virus control were implemented, by 2021, when vaccines were widely distributed and such measures were relaxed, it was estimated that US emissions increased by 6.2 percent. Geopolitical events such as the drastic rise in oil and gas prices stemming from Russia's invasion of Ukraine in early 2022 also, at times, inspired greater shifts in some countries toward more environmentally friendly energy alternatives.

In November 2022, a report published by the 27th Conference of the Parties to the United Nations Framework Convention on Climate Change (COP27) announced that carbon emissions from fossil fuels were expected to reach a record high in 2022 (and 5 percent higher than when the Paris Agreement was signed in 2015). Shortly after the conference, the Guardian reported that global greenhouse gas emissions would need to be halved by 2030 in order to reach the Paris Agreement's goal of limiting global warming to 1.5 degrees Celsius. In 2023, at the COP28 UN Climate Change Conference in the United Arab Emirates, delegates agreed to accelerate their transition away from fossil fuels to renewable energy sources in their climate commitments.

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