Chapter 2: Energy and the environment
300 to 400 million years ago
ocean
50 to 100 million years ago
small marine organisms
ocean today
trapped gas
sediment and rock impermeable rock porous sedimentary rock organisms turn into oil and natural gas
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porous sedimentary rock impermeable rock
trapped oil
sediment and rock
Figure 2.2 Oil and gas were formed in a similar way to coal. They are held in a layer of porous rock, which means they can be accessed by drilling.
In both cases the dead remains from animals and plants are buried under many layers of sediment, so extracting them involves digging or drilling deep underground. The length of time needed to create fossil fuels means that there is only a limited supply.
2.2 Energy resources The demand for energy is increasing worldwide. There are a number of reasons for this: •
increasing population size
•
increasing industrialisation and urbanisation
•
improvements in standards of living and expectations.
In order to meet the demand for energy, existing sources need to be used more efficiently and methods that until now have been too difficult or too expensive to use need to be explored further. Improvements in engineering and advances in technology may well reveal new opportunities.
Types of energy sources Different types of energy sources can be described by whether they are limited resources or available in unlimited supplies. Limited sources of energy are often described as being non-renewable: as they are used they cannot be replaced. Renewable sources of energy are those than can be replenished and therefore can be used over and over again.
Key terms
Non-renewable: an item or resource that exists in a finite amount that cannot be replaced Renewable: an item or resource that will not be used up or can be replaced