What you'll learn
This revision guide covers fossil fuels as energy resources for CIE IGCSE Environmental Management. You'll explore how coal, oil and natural gas form, their extraction methods, global distribution patterns, and the environmental consequences of their use. Understanding these non-renewable resources is essential for tackling questions on energy sustainability and environmental impact assessment.
Key terms and definitions
Fossil fuels — Non-renewable energy resources formed from the remains of dead organisms over millions of years, including coal, oil and natural gas.
Combustion — The chemical process of burning fuel in oxygen to release energy, producing carbon dioxide and water as main products.
Non-renewable resources — Natural resources that form so slowly that they cannot be replaced within a human timescale once extracted and used.
Hydrocarbon — An organic compound consisting entirely of hydrogen and carbon atoms, the main component of oil and natural gas.
Strip mining — Surface mining method where overlying rock and soil are removed to access near-surface mineral deposits, particularly coal seams.
Acid rain — Precipitation with a pH below 5.6 caused by atmospheric pollution, primarily from sulphur dioxide and nitrogen oxides dissolving in water droplets.
Carbon dioxide emissions — Release of CO₂ gas into the atmosphere, primarily from fossil fuel combustion, contributing to the enhanced greenhouse effect.
Peak oil — The theoretical point at which global petroleum extraction reaches its maximum rate, after which production enters terminal decline.
Core concepts
Formation of fossil fuels
Fossil fuels form through distinct geological processes over millions of years under specific conditions of heat and pressure.
Coal formation:
- Begins in swamp environments where plant material accumulates
- Dead vegetation becomes covered by sediment, preventing decay
- Pressure from overlying sediments compresses organic material
- Heat from Earth's interior drives chemical changes
- Progression: peat → lignite → bituminous coal → anthracite
- Process takes 50-300 million years
- Each stage has increasing carbon content and energy density
Oil and natural gas formation:
- Starts with marine organisms (plankton, algae) in shallow seas
- Organic material settles on seabed and mixes with sediment
- Burial under sediment layers creates heat and pressure
- Temperature range 50-150°C converts organic matter to hydrocarbons
- Oil forms at lower temperatures (50-100°C)
- Natural gas forms at higher temperatures (100-150°C)
- Process typically takes 10-180 million years
- Hydrocarbons migrate through porous rock until trapped by impermeable cap rock
Distribution and reserves
Fossil fuel deposits are unevenly distributed globally due to geological history and ancient environmental conditions.
Major coal reserves:
- United States (Appalachian Basin, Wyoming)
- China (Shanxi Province)
- India (Jharkhand, Odisha)
- Australia (Queensland, New South Wales)
- Russia (Siberia)
- Coal forms where ancient swamp forests existed
Major oil reserves:
- Middle East (Saudi Arabia, Iraq, UAE, Kuwait)
- Russia and Central Asia
- North America (United States, Canada - including tar sands)
- Venezuela (heavy oil deposits)
- West Africa (Nigeria, Angola)
- Concentrated in areas with ancient marine basins
Major natural gas reserves:
- Russia (largest global reserves)
- Iran and Qatar (sharing North Dome/South Pars field)
- United States (shale gas deposits)
- Turkmenistan
- Often found alongside oil deposits or separately in gas fields
Reserve lifetime estimates:
- Coal: approximately 130-150 years at current consumption rates
- Oil: approximately 50-60 years at current consumption rates
- Natural gas: approximately 50-70 years at current consumption rates
- These estimates change with new discoveries, extraction technology and consumption patterns
Extraction methods
Different extraction techniques apply depending on depth, geology and type of fossil fuel.
Coal mining methods:
Underground mining:
- Used when coal seams are deep (>100m below surface)
- Room and pillar method: coal extracted leaving pillars for roof support
- Longwall mining: mechanical shearers extract coal from long faces
- Requires extensive tunnel systems and ventilation
- Higher risk to worker safety (roof collapse, gas explosions)
- Less surface disturbance than surface mining
Surface mining:
- Strip mining for near-surface horizontal seams
- Opencast/open-pit mining for thick seams close to surface
- Mountaintop removal in mountainous terrain
- Removes overlying rock (overburden) to access coal
- More economical for shallow deposits
- Causes major landscape alteration
Oil extraction:
- Drilling through rock to reach underground reservoirs
- Onshore drilling uses vertical or directional wells
- Offshore drilling from platforms or floating rigs
- Primary recovery: natural pressure pushes oil up
- Secondary recovery: water or gas injection maintains pressure
- Tertiary recovery: chemicals or heat to extract remaining oil
- Hydraulic fracturing (fracking) releases oil from shale rock
Natural gas extraction:
- Conventional drilling into gas reservoirs
- Often co-produced with oil extraction
- Shale gas extraction through hydraulic fracturing
- Coal bed methane extraction from coal seams
- Requires pipeline infrastructure for transport
- Can be liquefied (LNG) for tanker transport
Environmental impacts of extraction
Fossil fuel extraction causes significant environmental damage at multiple scales.
Land degradation:
- Surface mining destroys existing ecosystems and soil structure
- Removal of vegetation and topsoil
- Creation of spoil heaps and waste rock piles
- Landscape scarring and altered topography
- Subsidence from underground mining causes surface collapse
- Opencast coal mines in Wales and former mining regions across UK show long-term impacts
Water pollution:
- Acid mine drainage from exposed sulphide minerals in coal mines
- Heavy metals (mercury, arsenic, lead) leach into waterways
- Oil spills during extraction and transport contaminate marine and freshwater environments
- Hydraulic fracturing risks groundwater contamination from chemicals
- Produced water from oil wells contains salts and hydrocarbons
- Sediment runoff from mining sites increases water turbidity
Habitat destruction:
- Complete loss of ecosystems in mining areas
- Fragmentation of surrounding habitats
- Displacement of wildlife populations
- Marine ecosystem damage from offshore drilling
- Mountaintop removal eliminates entire forest ecosystems
- Breeding grounds and migration routes disrupted
Air pollution from extraction:
- Dust emissions from coal mining and transport
- Methane leaks from coal mines and gas wells
- Flaring of excess gas releases CO₂ and particulates
- Diesel emissions from mining equipment
Environmental impacts of combustion
Burning fossil fuels for energy releases various pollutants with local, regional and global consequences.
Greenhouse gas emissions:
- Carbon dioxide (CO₂) is the primary greenhouse gas from combustion
- Methane (CH₄) leaks during extraction and transport
- Coal produces most CO₂ per unit energy (approximately 100kg CO₂/GJ)
- Oil produces approximately 75kg CO₂/GJ
- Natural gas produces approximately 55kg CO₂/GJ
- Accumulated atmospheric CO₂ drives climate change
- Global temperature rise, sea level rise, extreme weather events
Acid rain formation:
- Sulphur dioxide (SO₂) from sulphur impurities in coal and oil
- Nitrogen oxides (NOₓ) from high-temperature combustion
- These gases dissolve in atmospheric water forming acids:
- SO₂ + H₂O → H₂SO₃ (sulphurous acid)
- 2SO₂ + O₂ → 2SO₃, then SO₃ + H₂O → H₂SO₄ (sulphuric acid)
- NO₂ + H₂O → HNO₃ (nitric acid)
- Acidified precipitation damages:
- Forest ecosystems (leaf damage, soil nutrient leaching)
- Freshwater lakes and rivers (lower pH kills aquatic life)
- Buildings and monuments (limestone and marble dissolution)
- Agricultural soils (aluminum mobilization, nutrient loss)
Air quality impacts:
- Particulate matter (PM10, PM2.5) from incomplete combustion
- Coal combustion releases fly ash and soot
- Respiratory health problems (asthma, bronchitis, cardiovascular disease)
- Reduced visibility and smog formation
- Carbon monoxide from incomplete combustion (toxic gas)
- Heavy metals released: mercury, arsenic, lead
- Ground-level ozone formation from NOₓ and hydrocarbons in sunlight
Local pollution from power stations:
- Thermal pollution from cooling water discharge
- Waste ash disposal requires landfill space
- Visual pollution from cooling towers and chimney stacks
- Noise pollution from plant operations
Advantages and disadvantages of fossil fuels
Advantages:
- High energy density provides concentrated power source
- Established infrastructure for extraction, processing and distribution
- Relatively low cost per unit energy (though prices fluctuate)
- Reliable and dispatchable (available on demand)
- Technology for combustion well-developed and efficient
- Coal reserves widely distributed globally
- Natural gas burns cleaner than coal or oil
- Supports baseload electricity generation
- Existing workforce and expertise
Disadvantages:
- Non-renewable with finite reserves
- Major contributor to climate change via CO₂ emissions
- Air pollution causes health problems and environmental damage
- Extraction damages landscapes and ecosystems
- Risk of catastrophic accidents (oil spills, mine disasters)
- Price volatility creates economic uncertainty
- Geopolitical tensions over resource control
- Waste products require disposal
- Water consumption for cooling and processing
- Long-term legacy of environmental contamination
Worked examples
Example 1: Formation and extraction (6 marks)
Question: Explain how coal forms and describe one method used to extract it from the ground.
Mark scheme answer:
Formation (3 marks):
- Coal forms from dead plant material in swamp environments (1)
- Material becomes buried under sediment preventing decay (1)
- Heat and pressure over millions of years compress organic matter into coal (1)
- [Accept: progression through peat, lignite, bituminous coal stages]
Extraction method (3 marks):
- Strip mining removes overlying rock and soil (overburden) (1)
- This exposes near-surface coal seams for extraction (1)
- Large machinery excavates coal from the exposed seam (1)
OR
- Underground mining creates tunnels to reach deep coal seams (1)
- Room and pillar method removes coal while leaving support pillars (1)
- Coal is transported to surface through shaft systems (1)
Examiner note: Award maximum 3 marks for formation and 3 marks for extraction method. Specific terminology (overburden, seam, room and pillar) shows higher-level understanding.
Example 2: Environmental impacts (8 marks)
Question: Discuss the environmental impacts of burning coal in power stations to generate electricity.
Mark scheme answer:
Atmospheric impacts:
- Releases carbon dioxide contributing to enhanced greenhouse effect/climate change (1)
- Causes global temperature rise and associated impacts (1)
- Sulphur dioxide emissions lead to acid rain formation (1)
- Damages forests, acidifies lakes, erodes buildings (1)
- Particulate matter released causing air pollution (1)
- Respiratory health problems in nearby populations (1)
Other impacts:
- Thermal pollution from cooling water affecting aquatic ecosystems (1)
- Ash waste requires disposal in landfill sites (1)
- [Accept: heavy metal release, nitrogen oxide emissions, visual pollution]
Examiner note: For "discuss" questions, aim for balanced coverage. Award marks for identifying impacts (1 mark each) and explaining consequences (1 mark each). Quality over quantity—well-explained points score higher than lists.
Example 3: Comparing fossil fuels (4 marks)
Question: Compare the carbon dioxide emissions from burning coal and natural gas to generate the same amount of electricity.
Mark scheme answer:
- Coal produces more/higher CO₂ emissions per unit energy than natural gas (1)
- Coal releases approximately 100kg CO₂ per gigajoule (1)
- Natural gas releases approximately 55kg CO₂ per gigajoule (1)
- Natural gas is therefore less polluting/better for climate change than coal (1)
- [Accept: natural gas produces roughly half the emissions of coal for the same energy output]
Examiner note: "Compare" requires identifying both similarity and difference. Quantitative data strengthens answers. The conclusion linking to environmental impact shows analytical thinking.
Common mistakes and how to avoid them
Confusing renewable and non-renewable: Fossil fuels are always non-renewable because they take millions of years to form. Don't describe them as "running out slowly" without explaining they cannot be replaced on human timescales.
Vague formation explanations: Avoid "plants/animals died and turned into fossil fuels." Specify the type of organism (swamp plants for coal, marine organisms for oil/gas), the conditions (heat, pressure, absence of oxygen), and the timescale (millions of years).
Mixing up extraction methods: Strip mining and underground mining are both for coal but used in different geological situations. Don't confuse drilling (for oil/gas) with mining (for coal). Match the method to the depth and type of deposit.
Incomplete acid rain explanations: Don't just state "fossil fuels cause acid rain." Identify the specific gases (SO₂ and NOₓ), explain how they dissolve in water to form acids, and describe specific environmental impacts (forest damage, lake acidification, building erosion).
Ignoring carbon dioxide variations: Not all fossil fuels produce equal CO₂. Coal is most polluting, natural gas least polluting per unit energy. Use this in comparison questions to show detailed knowledge.
Oversimplifying advantages/disadvantages: Avoid one-word answers. "Pollution" needs specification—what type of pollution, what environmental or health impact? "Cheap" requires context—compared to what, and acknowledging price volatility.
Exam technique for "Energy Resources: Fossil Fuels"
Command word precision: "Describe" requires characteristics or features (what happens); "Explain" requires reasons or mechanisms (why/how it happens); "Discuss" requires examining different aspects, often advantages and disadvantages. Allocate time based on mark allocation—roughly 1 mark per minute.
Use specific examples: Generic answers score lower. Reference actual locations (Appalachian coalfields, North Sea oil), specific pollutants (SO₂, PM2.5), or quantitative data (coal = 100kg CO₂/GJ) to demonstrate detailed knowledge and access higher mark bands.
Structure comparison answers: When comparing fossil fuels, use a point-by-point approach. State the comparison criterion (e.g., CO₂ emissions), give data for each fuel type, then conclude which is better/worse and why. This logical structure ensures you cover both sides.
Link extraction to environmental impact: Questions often ask you to connect mining methods with their consequences. Strip mining → habitat destruction and landscape change; offshore drilling → risk of marine oil spills. Make these connections explicit rather than assuming the examiner will infer them.
Quick revision summary
Fossil fuels (coal, oil, natural gas) are non-renewable energy resources formed from ancient organic matter over millions of years. Coal forms from swamp plants; oil and gas from marine organisms. Extraction methods include surface and underground mining for coal, drilling for oil and gas. Combustion releases CO₂ (contributing to climate change), SO₂ and NOₓ (causing acid rain), and particulates (reducing air quality). While fossil fuels provide high energy density and reliable power, their environmental impacts and finite nature make them unsustainable long-term energy sources.