The Earth's Resources

- we rely on the Earth's natural resources to make new products and provide us with energy

- some of these natural resources are finite- they will run out eventually if we continue to epxloit them e.g. fossil fuels

- others are renewable- they can be replaced as we use them up e.g. crops used to make biofuels

- estimates of the time left before fossil fuels run out can only be rough estimates, because of the uncertainty involved in the calculations

- water is made fit to drink by passing it through filter beds to remove solids and adding chlorine, ozone or by passing ultra-violet light through it (sterilising) to reduce microbes

- water can be purified by distillation, but this requires large amounts of energy, which makes it expensive 

- reverse osmosis uses membranes to separate dissolved salts from salty water, but this method of desalination also uses energy to make the high pressures needed

- waste water requires treatment at a sewage works before being released into the environment 

- sewage treatment involves the removal of organic matter and harmful micro organisms and chemicals 

- the stages include screening to remove large solids and grit, sedimentation to produce sewage sludge, and aerobic biological treatment of the safe effluent released into environment

- the sewage sludge is separated, broken down by anaerobic digestion and dried. It can provide us with fertiliser and a source of renewable energy

- most copper is extracted by smelting (roasting) copper-rich ores, although supplies of ores are becoming scarcer

- copper can be extracted from solutions of copper compounds by electrolysis or by displacement using scrap iron. Electrolysis is also used to purify impure copper e.g. the copper metal obtained from smelting

- scientists are developing ways to extract copper that use low-grade copper ore. Bacteria are used in bioleaching and plants in phytomining

- life cycle assessments (LCAs) are carried out to assess the environmental impact of products, processes or services

- they analyse each of the stages of a life cycle, from extracting and processing raw material to disposal at the end of its useful life, including transport and distribution at each stage including transport and distribution 

- data is available for the use of energy, water, resources and production of some wastes

- however, assigning numerical values to the relative effects of pollutants involves subjective judgements, so LCAs using this approach must make this uncertainty clear 

- there are social, economic and environmental issues associated with exploiting the Earth's limited supplies of raw materials, such as metal ores

- recycling metals saves energy and our limited, finite metal ores (and fossil fuels)

- the pollution caused by the mining and extraction of metals is also reduced by recycling