AP Syllabus focus:
‘Natural energy resources such as ores, coal, crude oil, and natural gas are not evenly distributed worldwide because of geologic history.’
Energy resources are concentrated in specific places because Earth’s crust has formed, moved, and been reshaped over billions of years. Past environments, tectonics, and burial conditions determine where fuel and ore deposits can form and persist.
What “uneven distribution” means in APES
Uneven distribution describes where economically usable natural energy resources occur in the Earth, not where people use the most energy. The key control is geologic history: the sequence of deposition, burial, heating, deformation, and erosion that varies regionally over time.
Geologic history: The long-term record of rock formation and change in a region, including sediment deposition, tectonic movement, metamorphism, volcanism, and erosion.
Why geologic history controls energy-resource locations
1) Resources form only under specific past conditions
Many energy resources require rare combinations of materials and environmental settings.
Coal forms where large amounts of plant material accumulated (often swampy, low-oxygen settings) and were later buried.
Crude oil and natural gas originate from organic-rich sediments (often marine) that were buried and transformed by heat and pressure.
Metal ores used in energy technologies (e.g., copper for wiring) often form via magmatic or hydrothermal processes that occur mainly in certain tectonic settings.
If a region never had those past environments, it is unlikely to have that resource in significant quantities.
2) Plate tectonics create and move the right rock types
Plate tectonics builds mountain ranges, opens and closes ocean basins, and drives volcanism—processes that create the geological “ingredients” for deposits.
Convergent boundaries can generate volcanic arcs and hydrothermal fluids that concentrate metals into ore deposits.
Rifting and passive margins commonly create thick sedimentary basins that can host oil and gas systems.
Collisions and uplift can expose buried resources at the surface (or, alternatively, destroy or disperse deposits through deformation).
3) Burial depth and temperature determine fuel quality and existence
For fossil fuels, it’s not enough to have organic matter; it must experience the right thermal history.
Too little burial/heat: organic matter may not transform into oil or gas.
Too much heat: oil may “overmature” into gas, or organic material may be altered beyond useful fuels.
Variable burial histories across basins mean neighbouring regions can differ sharply in resource potential.
4) Geological structures trap or concentrate resources
Even if fuels form, they must be retained.
Oil and gas require traps (e.g., folds, faults, salt domes) plus impermeable cap rocks to prevent escape.
Ore minerals concentrate when fluids move through fractures and then cool or react chemically, depositing metals in limited zones.
Without these structures, resources can disperse or leak over geologic time.
5) Erosion, glaciation, and sea-level change redistribute or remove deposits
Surface-shaping processes affect whether deposits survive and whether humans can reach them.
Erosion can remove sedimentary layers (eliminating potential reservoirs) or expose seams/veins at the surface.
Glaciation can scour landscapes, bury areas under till, or transport sediments, changing where accessible deposits occur.
Sea-level changes influence sedimentation patterns, affecting where organic-rich layers or reservoir rocks were laid down.
Key takeaway patterns students should recognise
Energy resources cluster where the right rocks and right history coincide: sedimentary basins for many fossil fuels; tectonically active belts for many metal ores.
Sharp regional differences are expected because Earth’s crust evolved unevenly—different ages, different plate settings, different depositional environments.
FAQ
Basins form where the crust subsides (e.g., rifting, cooling of passive margins, foreland loading near mountains). Subsidence creates space for thick sediments, increasing the chance of organic-rich layers, reservoir rocks, and long burial histories.
A resource is the total amount thought to exist. A reserve is the portion that is proven and economically recoverable with current technology and prices. Geology sets the resource; economics and technology largely set the reserve.
Many critical ores concentrate in specific tectonic environments (e.g., subduction-related magmatism, hydrothermal systems). If a region lacked those conditions, it may have low-grade, dispersed metals that are harder to mine.
Yes. Tectonics can simultaneously create sedimentary basins (supporting fossil-fuel systems) and nearby magmatic/hydrothermal activity (forming metal ores). The exact outcomes depend on rock type, heat flow, and fluid pathways.
They combine field mapping with geophysics and geochemistry, for example:
Seismic surveys for basin structure and traps
Magnetic/gravity data for buried rock bodies
Geochemical signatures indicating organic richness or mineralising fluids
Practice Questions
Explain why crude oil and natural gas are not evenly distributed around the world. (2 marks)
Because they form only where specific past depositional environments produced organic-rich sediments (1).
Because suitable geologic history is required for burial/heating and trapping in reservoirs/cap rocks, which occur only in some regions (1).
Describe how geologic history can lead to concentrated coal deposits in some regions but not others. (5 marks)
Coal requires high plant productivity and accumulation in wetland/swamp conditions (1).
Low oxygen conditions reduce decomposition, allowing peat/organic matter to build up (1).
Subsequent burial by sediments is needed to compress and transform the material into coal (1).
Regional differences in tectonic subsidence and sedimentation control whether long-term burial occurs (1).
Uplift/erosion and later geologic change can expose, remove, or fragment deposits, affecting where coal remains accessible (1).
