| Gaia hypothesis
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| Term coined by James Lovelock to describe the earth's capacity to maintain the physical and chemical conditions necessary for life.
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| Galaxy
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| Grouping of billions of stars, gas, and dust, such as the Milky Way galaxy.
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| Gamma rays
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| Very short wavelength forms of the electromagnetic spectrum.
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| Gap analysis
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| A biogeographical technique of mapping biological diversity and endemic species to find gaps between protected areas that leave endangered habitats vulnerable to disruption.
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| Garden city
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| A new town with special emphasis on landscaping and rural ambience. gasohol A mixture of gasoline and ethanol.
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| Gasohol
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| A blend of 90% gasoline and 10% alcohol, which can be substituted for straight gasoline. It serves to stretch gasoline supplies.
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| Gene
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| A unit of heredity; a segment of DNA nucleus of the cell that contains information for the synthesis of a specific protein, such as an enzyme.
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| Gene banks
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| Storage for seed varieties for future breeding experiments.
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| Gene pool
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| The sum total of all the genes that exist amongall the individuals of a species.
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| General fertility rate
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| Representation of population age structure and fecundity; crude birthrate multiplied by the percentage of fecund women (between approximately fifteen and forty-four years of age) by 1,000.
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| Genetic assimilation
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| The disappearance of a species as its genes are diluted through crossbreeding with a closely related species.
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| Genetic bank
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| The concept that natural ecosystems with all their species serve as a tremendous repository of genes that is frequently drawn upon to improve domestic plants and animals and to develop new medicines, among other uses.
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| Genetic control
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| Selective breeding of the desired plant or animal to make it resistant to attack by pests. Also, attempting to introcluce harmful genes¡Xfor example, those that cause sterility¡X into the pest populations.
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| Genetic engineering
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| The artificial transfer of specific genes from one organism to another.
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| Genetic variation
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| An expression of the range of genetic (DNA) differences that occur among individuals of the same species.
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| Genetics
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| The study of heredity and the processes by which inherited characteristics are passed from one generation to the next.
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| Geometric growth
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| Growth that follows a geometric pattern of increase, such as 2, 4, 8, 16, etc. See exponential growth.
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| Geopressurized zone
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| Aquifer containing superheated, pressurized water and steam trapped by impermeable rock strata and heated by underlying magma.
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| Geothermal energy
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| Energy derived from the earth's heat that comes from decay of naturally occurring radioactive materials in the earth's crust, magma, and friction caused by movement of tectonic plates.
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| Geothermal
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| Refers to the naturally hot interior of Earth. The heat is maintained by naturally occurring nuclear reactions in Earth¡¦s interior.
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| Germ plasm
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| Genetic material that may be preserved for future agricultural, com mercial, and ecological values (plant seeds or parts or animal eggs, sperm, and embryos).
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| Global climate change
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| The term given to the various impacts of rising levels of greenhouse gases on Earth¡¦s climate. These effects include global warming, weather changes, and a rising sea level.
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| Global environmental citizenship
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| A shift in our attention from pollution in a specific place to a concern about the life-support systems of the whole planet.
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| Global environmentalism
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| A concern for, and action to help solve, global environmental problems.
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| Glucose
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| A simple sugar, the major product of photosynthesis. Serves as the basic building block for cellulose and starches and as the major ¡§fuel¡¨ for the release of energy through cell respiration in both plants and animals.
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| Gradualism
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| Theory of evolution holding that species evolve over long periods. Contrast with punctuated equilibrium.
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| Grasslands
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| Biome found in both temperate and tropical regions and characterized by periodic drought, flat or slightly rolling terrain, and large grazers that feed off the lush grasses.
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| Grassroots movement
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| An environmental movement that begins at the level of the populace, often in response to a perceived problem not being addressed by public policy.
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| Gravitational water
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| Water that is not held by capillary action in soil but percolates downward by the force of gravity.
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| Gray water
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| Wastewater, as from sinks and tubs, that does not contain human excrements. Such water can be reused without purification for some purposes.
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| Gray-air cities
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| Older industrial cities characterized by predom inantly sulfur dioxide and particulate pollution. Contrast with brown-air cities.
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| Graying
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| The increasing average age in populations in developed and many developing countries that is occurring because of decreasing birth rates and increasing longevity.
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| Grazer food chain
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| A specific nutrient and energy pathway start ing with plants that are consumed by grazers (herbivores).
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| Green fee
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| An added cost for a particular service or product that has the effect of internalizing the external costs and reflects the real environmental cost of the activity.
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| Green manure
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| A legume crop such as clover that is specifically grown to enrich the nitrogen and organic content of soil.
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| Green plans
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| Integrated national environmental plans for reducing pollution and resource consumption while achieving sustainable development and environmental restoration.
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| Green political parties
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| Political organizations based on environmental protection, participatory democracy, grassroots organization, and sustainable development.
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| Green products
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| Products that are more environmentally benign than their traditional counterparts.
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| Green revolution
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| Dramatically increased agricultural production brought about by ¡§miracle¡¨ strains of grain; usually requires high inputs of water, plant nutrients, and pesticides.
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| Greenhouse effect
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| An increase in the atmospheric temperature caused by increasing amounts of carbon dioxide and certain other gases that absorb and trap heat radiation, which normally escapes from Earth.
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| Greenhouse gases
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| Gases in the atmosphere that absorb infrared energy and contribute to the air temperature. These gases are like a heat blanket and are important in insulating Earth¡¦s surface. They include carbon dioxide, water vapor, methane, nitrous oxide, and chlorofluorocarbons and other halocarbons.
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| Grit chamber
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| Part of preliminary treatment in wastewater-treatment plants; a swimming pool¡Xlike tank in which the velocity of the water is slowed enough to let sand and other gritty material settle.
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| Grit-settling tank
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| See grit chamber.
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| Gross domestic (national) product per capita
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| The total value of all goods and services exchanged in a year in a country, divided by its population. A common indicator for the average level of development and standard of living for a country.
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| Gross national product (GNP)
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| The sum total of all goods and services produced in a national economy. Gross domestic product (GDP) is used to distinguish economic activity within a country from that of off-shore corporations.
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| Gross primary production
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| The rate at which primary producers in ecosystems are fixing organic matter.
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| Groundwater
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| Water held in gravel deposits or porous rock below the earth¡¦s surface; does not include water or crystallization held by chemical bonds in rocks or moisture in upper soil layers.
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| Groundwater remediation
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| The repurification of contaminated groundwater by any of a number of techniques.
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| Gully erosion
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| Removal of layers of soil, creating channels or ravines too large to be removed by normal tillage operations.
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