– Plants and animals reproduce, and therefore, as long as some mature individuals of a species survive, they can be replaced.

– A sustainable yield results when renewable resources are replaced at the same rate at which they are consumed.

– Sunlight is considered to be a renewable resource because it will continue to be available for at least the next 5 billion years.

– Land provides places for humans and other organisms to live and interact.

– Land also provides spaces for the growth of crops, forests, grasslands, and for wilderness areas.

• The loss of topsoil makes soil less fertile and less able to hold water, which results in poorer crops.

• Topsoil is currently eroding faster than it forms on about one-third of Earth’s croplands.

• Desertification can be prevented by reducing overgrazing and by planting trees and shrubs to anchor soils and retain water.

• Bedrock is a base of unweathered parent rock underlying the soil that may consist of limestone, granite, marble, or other rocks that can be mined in quarries.

• Aggregates are found in river valleys, and in glacial moraines, eskers, kames, and outwash plains.

• Aggregates used in construction are mixed with cement, lime, gypsum, or other materials to form concrete.

• Ores can be classified by the manner in which they formed.

• Some ores are associated with igneous rocks, whereas others are formed by processes at Earth’s surface.

– Ores associated with igneous rocks may contain iron, chromium, and platinum. – Chromium and platinum ores can form when minerals crystallize and settle to the bottom of a cooling body

of magma.

– Hydrothermal fluids are the most important sources of metallic ore deposits. – Atoms of metals such as copper and gold do not fit into the crystals that form during the cooling process and become concentrated in the

remaining magma. – Eventually, a solution rich in metals and silica moves into the surrounding rocks to create ore deposits, known as hydrothermal veins, along faults

and joints.

– Heavy sediments, such as grains of gold and silver, may be deposited in bars of sand and gravel when stream velocity decreases.

– Placer deposits are sand and gravel bars that contain heavier sediments such as gold nuggets, gold dust, diamonds, platinum, and gemstones, as well as rounded pebbles of tin and titanium oxides.

• Salt, or sodium chloride, occurs in deposits both on Earth’s surface and underground.

• Deposits of both salt and gypsum, which is used to make plaster, can form when seawater evaporates.

– Mines can destroy the original ground contours and leave behind waste rock that can release pollutants.

– Gangue, which is the material left after ore is extracted through grinding the parent rock, may release harmful chemicals into groundwater or surface water.

– Reclamation, reclaiming of desert, marshy, or submerged areas or other wasteland for cultivation or other use.

• The oceans help regulate climate, provide habitats for marine organisms, and dilute many pollutants.

• Most animals are about 50 to 75 percent water by weight, and even trees may be composed of up to 60 percent water.

– Although the U.S. has plenty of freshwater, much of it is concentrated in the eastern states or has been contaminated by agricultural or industrial processes.

– About 25 countries, primarily in Africa, experience chronic water shortages.

– About 70 percent of the water withdrawn each year is used to irrigate the world’s croplands.

– About 23 percent of freshwater is used for cooling purposes in power plants, for oil and gas production, and in industrial processing.

– About 7 percent goes to domestic uses.

– Desalination is the process of removing salt from ocean water to provide freshwater. • The water is first heated until it evaporates, then it

is condensed and collected. • The evaporation process leaves the salts behind. • Most countries that use desalination to produce freshwater use solar energy to evaporate sea water.

• Biomass fuels, which are fuels derived from living things, are widely used in many developing countries.

• Wood is the most commonly used traditional biomass fuel.

• Fossil fuels are considered to be nonrenewable because their formation occurred over thousands or even millions of years.

• Fossil fuels include peat, coal, natural gas, and petroleum.

– Coal formed from compressed organic matter at the bottom of ancient swamps in which the carbon concentration increased as oxygen and hydrogen were lost.

– The higher the carbon concentration, the hotter and cleaner the coal burns.

• Some experts estimate that petroleum resources may be used up within the next 60 years.

• Renewable alternatives to traditional energy resources include solar energy, wind, water, geothermal energy, nuclear energy, and biomass.

• The main advantages of solar energy are that it is free and it doesn’t cause any kind of pollution.

– The Sun’s energy also can be captured to be released during the evening in floors and walls made of concrete, adobe, brick, stone, or tile, which have heat-storing capacities.

– Passive solar designs can provide up to 70 percent of the energy needed to heat a house.

– Active solar-heating systems include collectors such as solar panels that absorb solar energy and fans or pumps that distribute that energy throughout the house.

– Heat collected by the solar panels can be used to heat a house directly, or it can be stored for later use.

– Photovoltaic cells, transparent wafers made up of layers of boron- and phosphorus-enriched silicon, convert solar energy into electrical energy.

– The electricity produced by photovoltaic cells can be stored in batteries.– It is estimated that power towers may someday supply 30 percent of the electric

power used worldwide.

• Currently provides about 20 percent of the world’s electricity and 6 percent of its total energy.

• One advantage of hydroelectric power is that it is nonpolluting.

• Dams built have negative impacts including flooding large areas, destroying habitats, and changing the natural pattern of water flow.

• Abundant at some surface locations usually coinciding with plate boundaries. If developed, geothermal reservoirs in the U.S. could possibly provide up to 30 times as much energy as the country currently uses.

– Wind is a virtually unlimited energy resource.– Wind energy is one of the least expensive ways to produce electricity, but it is economical only in areas with steady

winds. – Wind farms are not very attractive and they have been shown to interfere with and even kill migrating birds.

• Wind power could supply more than 10 percent of the world’s electricity by the year 2050.

• Uranium is a radioactive element that is commonly used in the production of nuclear energy.

• Poor management, high operating costs, poor reactor designs, and public concerns about safety and disposal of radioactive wastes contributed to the decline of nuclear power.

• Bacteria and chemical processes can be used to convert solid biomass into gaseous and liquid biofuels, such as biogas, liquid ethanol, and liquid methanol.

• A disadvantage of biomass fuels is that when they are burned, they release carbon dioxide and particulate matter into the atmosphere.