| A | B |
|---|
| acid rain | A mixture of acid and rain water that falls to the earth |
| biomass energy | Plant or animal material from living or recently living things that can be changed into fuel |
| conservation | All the practices that preserve and wisely use natural resources |
| contour plowing | A method of plowing at right angles to the slope of the land to prevent water from carrying soil downhill |
| cover crops | Crops like hay and wheat that completely cover the soil, forming a grassy area that holds water |
| crop rotation | The practice of growing different kinds of plants in a given area each season |
| endangered species | A species that is in danger of becoming extinct |
| extinct | Species of organisms of the past that no longer exist |
| fossil fuel | Fuel that was formed over millions of years from the remains of once-living things |
| geothermal energy | Energy that comes from heat beneath the earth's surface |
| geyser | Hot underground water that shoots out of the ground through an opening |
| humus | The decaying remains of dead plants and animals (found in topsoil) |
| natural resources | Materials from the earth that are needed by humans |
| nonrenewable resources | Materials from the earth that are needed by humans and that are not replaced |
| nuclear energy | Energy that is released when the structure of atoms is changed |
| nuclear fission | The splitting of atoms to release energy |
| nuclear fusion | A process in which energy is given off when two atoms are joined |
| pollutant | A material that harms the environment |
| pollution | The introduction of unwanted, usually harmful materials into an environment |
| recycling | A process in which wastes are used to make new products |
| renewable resources | Materials from the earth that are used by humans and that can be replaced through natural cycles |
| reservoir | A place where fresh water is stored |
| solar cells | Devices that change sunlight directly into electricity |
| solar energy | Energy from the sun |
| strip cropping | A farming method in which strips of cover crops are planted between strips of other crops |
| thermal pollution | Pollution caused by the release of waste heat into the environment |
| tidal energy | Energy released by the movement of ocean tides, waves, and currents |
| watershed | A land area that supplies water to a river or other body of fresh water |
