• pollution
    Garbage in, garbage out.

    Photograph by Dennis Finley

    Indoor Air Pollution
    The air inside your house can be polluted. Air and carpet cleaners, insect sprays, and cigarettes are all sources of indoor air pollution.

    How Long Does It Last?
    Different materials decompose at different rates. How long does it take for these common types of trash to break down?

    • Paper: 2-4 weeks
    • Orange peel: 6 months
    • Milk carton: 5 years
    • Plastic bag: 15 years
    • Tin can: 100 years
    • Plastic bottle: 450 years
    • Glass bottle: 500 years
    • Styrofoam: Never

    Noise Pollution
    Noise pollution is the constant presence of loud, disruptive noises in an area. Usually, noise pollution is caused by construction or nearby transportation facilities, such as airports.

    Noise pollution is unpleasant, and can be dangerous. Some songbirds, such as robins, are unable to communicate or find food in the presence of heavy noise pollution. The sound waves produced by some noise pollutants can disrupt the sonar used by marine animals to communicate or locate food.

    Light Pollution
    Light pollution is the excess amount of light in the night sky. Light pollution, also called photopollution, is almost always found in urban areas. Light pollution can disrupt ecosystems by confusing the distinction between night and day. Nocturnal animals, those that are active at night, may venture out during the day, while diurnal animals, which are active during daylight hours, may remain active well into the night. Feeding and sleep patterns may be confused. Light pollution also indicates an excess use of energy.

    The dark-sky movement is a campaign by people to reduce light pollution. This would reduce energy use, allow ecosystems to function more normally, and allow scientists and stargazers to observe the atmosphere.

    Pollution is the introduction of harmful materials into the environment. These harmful materials are called pollutants. Pollutants can be natural, such as volcanic ash. They can also be created by human activity, such as trash or runoff produced by factories. Pollutants damage the quality of air, water, and land.

    Many things that are useful to people produce pollution. Cars spew pollutants from their exhaust pipes. Burning coal to create electricity pollutes the air. Industries and homes generate garbage and sewage that can pollute the land and water. Pesticides—chemical poisons used to kill weeds and insects—seep into waterways and harm wildlife.

    All living things—from one-celled microbes to blue whales—depend on Earth’s supply of air and water. When these resources are polluted, all forms of life are threatened.

    Pollution is a global problem. Although urban areas are usually more polluted than the countryside, pollution can spread to remote places where no people live. For example, pesticides and other chemicals have been found in the Antarctic ice sheet. In the middle of the northern Pacific Ocean, a huge collection of microscopic plastic particles forms what is known as the Great Pacific Garbage Patch.

    Air and water currents carry pollution. Ocean currents and migrating fish carry marine pollutants far and wide. Winds can pick up radioactive material accidentally released from a nuclear reactor and scatter it around the world. Smoke from a factory in one country drifts into another country.

    In the past, visitors to Big Bend National Park in the U.S. state of Texas could see 290 kilometers (180 miles) across the vast landscape. Now, coal-burning power plants in Texas and the neighboring state of Chihuahua, Mexico have spewed so much pollution into the air that visitors to Big Bend can sometimes see only 50 kilometers (30 miles).

    The three major types of pollution are air pollution, water pollution, and land pollution.

    Air Pollution


    Sometimes, air pollution is visible. A person can see dark smoke pour from the exhaust pipes of large trucks or factories, for example. More often, however, air pollution is invisible.

    Polluted air can be dangerous, even if the pollutants are invisible. It can make people’s eyes burn and make them have difficulty breathing. It can also increase the risk of lung cancer.

    Sometimes, air pollution kills quickly. In 1984, an accident at a pesticide plant in Bhopal, India, released a deadly gas into the air. At least 8,000 people died within days. Hundreds of thousands more were permanently injured.

    Natural disasters can also cause air pollution to increase quickly. When volcanoes erupt, they eject volcanic ash and gases into the atmosphere. Volcanic ash can discolor the sky for months. After the eruption of the Indonesian volcano of Krakatoa in 1883, ash darkened the sky around the world. The dimmer sky caused fewer crops to be harvested as far away as Europe and North America. For years, meteorologists tracked what was known as the “equatorial smoke stream.” In fact, this smoke stream was a jet stream, a wind high in Earth’s atmosphere that Krakatoa’s air pollution made visible.

    Volcanic gases, such as sulfur dioxide, can kill nearby residents and make the soil infertile for years. Mount Vesuvius, a volcano in Italy, famously erupted in 79, killing hundreds of residents of the nearby towns of Pompeii and Herculaneum. Most victims of Vesuvius were not killed by lava or landslides caused by the eruption. They were choked, or asphyxiated, by deadly volcanic gases.

    In 1986, a toxic cloud developed over Lake Nyos, Cameroon. Lake Nyos sits in the crater of a volcano. Though the volcano did not erupt, it did eject volcanic gases into the lake. The heated gases passed through the water of the lake and collected as a cloud that descended the slopes of the volcano and into nearby valleys. As the toxic cloud moved across the landscape, it killed birds and other organisms in their natural habitat. This air pollution also killed thousands of cattle and as many as 1,700 people.

    Most air pollution is not natural, however. It comes from burning fossil fuels—coal, oil, and natural gas. When gasoline is burned to power cars and trucks, it produces carbon monoxide, a colorless, odorless gas. The gas is harmful in high concentrations, or amounts. City traffic produces highly concentrated carbon monoxide.

    Cars and factories produce other common pollutants, including nitrogen oxide, sulfur dioxide, and hydrocarbons. These chemicals react with sunlight to produce smog, a thick fog or haze of air pollution. The smog is so thick in Linfen, China, that people can seldom see the sun. Smog can be brown or grayish blue, depending on which pollutants are in it.

    Smog makes breathing difficult, especially for children and older adults. Some cities that suffer from extreme smog issue air pollution warnings. The government of Hong Kong, for example, will warn people not to go outside or engage in strenuous physical activity (such as running or swimming) when smog is very thick.


    When air pollutants such as nitrogen oxide and sulfur dioxide mix with moisture, they change into acids. They then fall back to earth as acid rain. Wind often carries acid rain far from the pollution source. Pollutants produced by factories and power plants in Spain can fall as acid rain in Norway.

    Acid rain can kill all the trees in a forest. It can also devastate lakes, streams, and other waterways. When lakes become acidic, fish can’t survive. In Sweden, acid rain created thousands of “dead lakes,” where fish no longer live.

    Acid rain also wears away marble and other kinds of stone. It has erased the words on gravestones and damaged many historic buildings and monuments. The Taj Mahal, in Agra, India, was once gleaming white. Years of exposure to acid rain has left it pale.

    Governments have tried to prevent acid rain by limiting the amount of pollutants released into the air. In Europe and North America, they have had some success, but acid rain remains a major problem in the developing world, especially Asia.  

    Greenhouse gases are another source of air pollution. Greenhouse gases such as carbon dioxide and methane occur naturally in the atmosphere. In fact, they are necessary for life on Earth. They absorb sunlight reflected from Earth, preventing it from escaping into space. By trapping heat in the atmosphere, they keep Earth warm enough for people to live. This is called the greenhouse effect.

    But human activities such as burning fossil fuels and destroying forests have increased the amount of greenhouse gases in the atmosphere. This has increased the greenhouse effect, and average temperatures across the globe are rising. The decade that began in the year 2000 was the warmest on record. This increase in worldwide average temperatures, caused in part by human activity, is called global warming.

    Global warming is causing ice sheets and glaciers to melt. The melting ice is causing sea levels to rise at a rate of 2 millimeters (0.09 inches) per year. The rising seas will eventually flood low-lying coastal regions. Entire nations, such as the islands of Maldives, are threatened by this climate change.

    Global warming also contributes to the phenomenon of ocean acidification. Ocean acidification is the process of ocean waters absorbing more carbon dioxide from the atmosphere. Fewer organisms can survive in warmer, less salty waters. The ocean food web is threatened as plants and animals such as coral fail to adapt to more acidic oceans.

    Scientists have predicted that global warming will cause an increase in severe storms. It will also cause more droughts in some regions and more flooding in others.

    The change in average temperatures is already shrinking some habitats, the regions where plants and animals naturally live. Polar bears hunt seals from sea ice in the Arctic. The melting ice is forcing polar bears to travel farther to find food, and their numbers are shrinking.

    People and governments can respond quickly and effectively to reduce air pollution. Chemicals called chlorofluorocarbons (CFCs) are a dangerous form of air pollution that governments worked to reduce in the 1980s and 1990s. CFCs are found in gases that cool refrigerators, in foam products, and in aerosol cans.

    CFCs damage the ozone layer, a region in Earth’s upper atmosphere. The ozone layer protects Earth by absorbing much of the sun’s harmful ultraviolet radiation. When people are exposed to more ultraviolet radiation, they are more likely to develop skin cancer, eye diseases, and other illnesses.

    In the 1980s, scientists noticed that the ozone layer over Antarctica was thinning. This is often called the “ozone hole.” No one lives permanently in Antarctica. But Australia, the home of more than 22 million people, lies at the edge of the hole. In the 1990s, the Australian government began an effort to warn people of the dangers of too much sun. Many countries, including the United States, now severely limit the production of CFCs.

    Water Pollution

    Some polluted water looks muddy, smells bad, and has garbage floating in it. Some polluted water looks clean, but is filled with harmful chemicals you can’t see or smell.

    Polluted water is unsafe for drinking and swimming. Some people who drink polluted water are exposed to hazardous chemicals that may make them sick years later. Others consume bacteria and other tiny aquatic organisms that cause disease. The United Nations estimates that 4,000 children die every day from drinking dirty water.

    Sometimes, polluted water harms people indirectly. They get sick because the fish that live in polluted water are unsafe to eat. They have too many pollutants in their flesh.

    There are some natural sources of water pollution. Oil and natural gas, for example, can leak into oceans and lakes from natural underground sources. These sites are called petroleum seeps. The world’s largest petroleum seep is the Coal Oil Point Seep, off the coast of the U.S. state of California. The Coal Oil Point Seep releases so much oil that tar balls wash up on nearby beaches. Tar balls are small, sticky pieces of pollution that eventually decompose in the ocean.


    Human activity also contributes to water pollution. Chemicals and oils from factories are sometimes dumped or seep into waterways. These chemicals are called runoff. Chemicals in runoff can create a toxic environment for aquatic life. Runoff can also help create a fertile environment for cyanobacteria, also called blue-green algae. Cyanobacteria reproduce rapidly, creating a harmful algal bloom (HAB). Harmful algal blooms prevent organisms such as plants and fish from living in the ocean. They are associated with “dead zones” in the world’s lakes and rivers, places where little life exists below surface water.

    Mining and drilling can also contribute to water pollution. Acid mine drainage (AMD) is a major contributor to pollution of rivers and streams near coal mines. Acid helps miners remove coal from the surrounding rocks. The acid is washed into streams and rivers, where it reacts with rocks and sand. It releases chemical sulfur from the rocks and sand, creating a river rich in sulfuric acid. Sulfuric acid is toxic to plants, fish, and other aquatic organisms. Sulfuric acid is also toxic to people, making rivers polluted by AMD dangerous sources of water for drinking and hygiene.

    Oil spills are another source of water pollution. In April 2010, the Deepwater Horizon oil rig exploded in the Gulf of Mexico, causing oil to gush from the ocean floor. In the following months, hundreds of millions of gallons of oil spewed into the gulf waters. The spill produced large plumes of oil under the sea and an oil slick on the surface as large as 24,000 square kilometers (9,100 square miles). The oil slick coated wetlands in the U.S. states of Louisiana and Mississippi, killing marsh plants and aquatic organisms such as crabs and fish. Birds, such as pelicans, became coated in oil and were unable to fly or access food. More than 2 million animals died as a result of the Deepwater Horizon oil spill.

    Buried chemical waste can also pollute water supplies. For many years, people disposed of chemical wastes carelessly, not realizing its dangers. In the 1970s, people living in the Love Canal area in Niagara Falls, New York, suffered from extremely high rates of cancer and birth defects. It was discovered that a chemical waste dump had poisoned the area’s water. In 1978, 800 families living in Love Canal had to abandon their homes.

    If not disposed of properly, radioactive waste from nuclear power plants can escape into the environment. Radioactive waste can harm living things and pollute the water.

    Sewage that has not been properly treated is a common source of water pollution. Many cities around the world have poor sewage systems and sewage treatment plants. Delhi, the capital of India, is home to more than 21 million people. More than half the sewage and other waste produced in the city are dumped into the Yamuna River. This pollution makes the river dangerous to use as a source of water for drinking or hygiene. It also reduces the river’s fishery, resulting in less food for the local community.

    A major source of water pollution is fertilizer used in agriculture. Fertilizer is material added to soil to make plants grow larger and faster. Fertilizers usually contain large amounts of the elements nitrogen and phosphorus, which help plants grow. Rainwater washes fertilizer into streams and lakes. There, the nitrogen and phosphorus cause cyanobacteria to form harmful algal blooms.

    Rain washes other pollutants into streams and lakes. It picks up animal waste from cattle ranches. Cars drip oil onto the street, and rain carries it into storm drains, which lead to waterways such as rivers and seas. Rain sometimes washes chemical pesticides off of plants and into streams. Pesticides can also seep into groundwater, the water beneath the surface of the Earth.

    Heat can pollute water. Power plants, for example, produce a huge amount of heat. Power plants are often located on rivers so they can use the water as a coolant. Cool water circulates through the plant, absorbing heat. The heated water is then returned to the river. Aquatic creatures are sensitive to changes in temperature. Some fish, for example, can only live in cold water. Warmer river temperatures prevent fish eggs from hatching. Warmer river water also contributes to harmful algal blooms.

    Another type of water pollution is simple garbage. The Citarum River in Indonesia, for example, has so much garbage floating in it that you cannot see the water. Floating trash makes the river difficult to fish in. Aquatic animals such as fish and turtles mistake trash, such as plastic bags, for food. Plastic bags and twine can kill many ocean creatures. Chemical pollutants in trash can also pollute the water, making it toxic for fish and people who use the river as a source of drinking water. The fish that are caught in a polluted river often have high levels of chemical toxins in their flesh. People absorb these toxins as they eat the fish.

    Garbage also fouls the ocean. Many plastic bottles and other pieces of trash are thrown overboard from boats. The wind blows trash out to sea. Ocean currents carry plastics and other floating trash to certain places on the globe, where it cannot escape. The largest of these areas, called the Great Pacific Garbage Patch, is in a remote part of the Pacific Ocean. According to some estimates, this garbage patch is the size of Texas. The trash is a threat to fish and seabirds, which mistake the plastic for food. Many of the plastics are covered with chemical pollutants.

    Land Pollution


    Many of the same pollutants that foul the water also harm the land. Mining sometimes leaves the soil contaminated with dangerous chemicals.

    Pesticides and fertilizers from agricultural fields are blown by the wind. They can harm plants, animals, and sometimes people. Some fruits and vegetables absorb the pesticides that help them grow. When people consume the fruits and vegetables, the pesticides enter their bodies. Some pesticides can cause cancer and other diseases.


    A pesticide called DDT (dichlorodiphenyltrichloroethane) was once commonly used to kill insects, especially mosquitoes. In many parts of the world, mosquitoes carry a disease called malaria, which kills a million people every year. Swiss chemist Paul Hermann Muller was awarded the Nobel Prize for his understanding of how DDT can control insects and other pests. DDT is responsible for reducing malaria in places such as Taiwan and Sri Lanka.

    In 1962, American biologist Rachel Carson wrote a book called Silent Spring, which discussed the dangers of DDT. She argued that it could contribute to cancer in humans. She also explained how it was destroying bird eggs, which caused the number of bald eagles, brown pelicans, and ospreys to drop. In 1972, the United States banned the use of DDT. Many other countries also banned it. But DDT didn’t disappear entirely. Today, many governments support the use of DDT because it remains the most effective way to combat malaria.

    Trash is another form of land pollution. Around the world, paper, cans, glass jars, plastic products, and junked cars and appliances mar the landscape. Litter makes it difficult for plants and other producers in the food web to create nutrients. Animals can die if they mistakenly eat plastic.

    Garbage often contains dangerous pollutants such as oils, chemicals, and ink. These pollutants can leech into the soil and harm plants, animals, and people.

    Inefficient garbage collection systems contribute to land pollution. Often, the garbage is picked up and brought to a dump, or landfill. Garbage is buried in landfills. Sometimes, communities produce so much garbage that their landfills are filling up. They are running out of places to dump their trash.

    A massive landfill near Quezon City, Philippines, was the site of a land pollution tragedy in 2000. Hundreds of people lived on the slopes of the Quezon City landfill. These people made their living from recycling and selling items found in the landfill. However, the landfill was not secure. Heavy rains caused a trash landslide, killing 218 people.

    Sometimes, landfills are not completely sealed off from the land around them. Pollutants from the landfill leak into the earth in which they are buried. Plants that grow in the earth may be contaminated, and the herbivores that eat the plants also become contaminated. So do the predators that consume the herbivores. This process, where a chemical builds up in each level of the food web, is called bioaccumulation.

    Pollutants leaked from landfills also leak into local groundwater supplies. There, the aquatic food web (from microscopic algae to fish to predators such as sharks or eagles) can suffer from bioaccumulation of toxic chemicals.

    Some communities do not have adequate garbage collection systems, and trash lines the side of roads. In other places, garbage washes up on beaches. Kamilo Beach, in the U.S. state of Hawaii, is littered with plastic bags and bottles carried in by the tide. The trash is dangerous to ocean life and reduces economic activity in the area. Tourism is Hawaii’s largest industry. Polluted beaches discourage tourists from investing in the area’s hotels, restaurants, and recreational activities.

    Some cities incinerate, or burn, their garbage. Incinerating trash gets rid of it, but it can release dangerous heavy metals and chemicals into the air. So while trash incinerators can help with the problem of land pollution, they sometimes add to the problem of air pollution.

    Reducing Pollution


    Around the world, people and governments are making efforts to combat pollution. Recycling, for instance, is becoming more common. In recycling, trash is processed so its useful materials can be used again. Glass, aluminum cans, and many types of plastic can be melted and reused. Paper can be broken down and turned into new paper.

    Recycling reduces the amount of garbage that ends up in landfills, incinerators, and waterways. Austria and Switzerland have the highest recycling rates. These nations recycle between 50 and 60 percent of their garbage. The United States recycles about 30 percent of its garbage.

    Governments can combat pollution by passing laws that limit the amount and types of chemicals factories and agribusinesses are allowed to use. The smoke from coal-burning power plants can be filtered. People and businesses that illegally dump pollutants into the land, water, and air can be fined for millions of dollars. Some government programs, such as the Superfund program in the United States, can force polluters to clean up the sites they polluted.

    International agreements can also reduce pollution. The Kyoto Protocol, a United Nations agreement to limit the emission of greenhouse gases, has been signed by 191 countries. The United States, the world’s second-largest producer of greenhouse gases, did not sign the agreement. Other countries, such as China, the world’s largest producer of greenhouse gases, have not met their goals.  

    Still, many gains have been made. In 1969, the Cuyahoga River, in the U.S. state of Ohio, was so clogged with oil and trash that it caught on fire. The fire helped spur the Clean Water Act of 1972. This law limited what pollutants could be released into water and set standards for how clean water should be. Today, the Cuyahoga River is much cleaner. Fish have returned to regions of the river where they once could not survive.

    But even as some rivers are becoming cleaner, others are becoming more polluted. As countries around the world become wealthier, some forms of pollution increase. Countries with growing economies usually need more power plants, which produce more pollutants.

    Reducing pollution requires environmental, political, and economic leadership. Developed nations must work to reduce and recycle their materials, while developing nations must work to strengthen their economies without destroying the environment. Developed and developing countries must work together toward the common goal of protecting the environment for future use.

  • Term Part of Speech Definition Encyclopedic Entry
    absorb Verb

    to soak up.

    acid Noun

    chemical compound that reacts with a base to form a salt. Acids can corrode some natural materials. Acids have pH levels lower than 7.

    acid mine drainage Noun

    flow of acid or acidic liquid from metal mines or coal mines.

    acid rain Noun

    precipitation with high levels of nitric and sulfuric acids. Acid rain can be manmade or occur naturally.

    adapt Verb

    to adjust to new surroundings or a new situation.

    adequate Adjective

    suitable or good enough.

    aerosol can Noun

    container of liquid material under high pressure. When released through a small opening, the liquid becomes a spray or foam.

    agribusiness Noun

    the strategy of applying profit-making practices to the operation of farms and ranches.

    agriculture Noun

    the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

    Encyclopedic Entry: agriculture
    air pollution Noun

    harmful chemicals in the atmosphere.

    Encyclopedic Entry: air pollution
    algae Plural Noun

    (singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.

    aluminum Noun

    silvery, reflective metallic element with the symbol Al.

    Antarctic Noun

    region at Earth's extreme south, encompassed by the Antarctic Circle.

    aquatic Adjective

    having to do with water.

    asphyxiate Verb

    to choke or suffocate.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    bacteria Plural Noun

    (singular: bacterium) single-celled organisms found in every ecosystem on Earth.

    ban Verb

    to prohibit, or not allow.

    beach Noun

    narrow strip of land that lies along a body of water.

    Encyclopedic Entry: beach
    bioaccumulation Noun

    process by which chemicals are absorbed by an organism, either from exposure to a substance with the chemical or by consumption of food containing the chemical.

    biologist Noun

    scientist who studies living organisms.

    birth defect Noun

    physical disorder present at birth and not developed later.

    blue-green algae Noun

    type of aquatic bacteria (not algae) that can photosynthesize light to create energy. Also called cyanobacteria and (in freshwater habitats) pond scum.

    cancer Noun

    growth of abnormal cells in the body.

    capital Noun

    city where a region's government is located.

    Encyclopedic Entry: capital
    carbon dioxide Noun

    greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

    carbon monoxide Noun

    toxic gas.

    cattle Noun

    cows and oxen.

    chlorofluorocarbon (CFC) Noun

    chemical compound mostly used in refrigerants and flame-retardants. Some CFCs have destructive effects on the ozone layer.

    circulate Verb

    to move around, often in a pattern.

    Clean Water Act Noun

    (1972) federal law protecting water from pollution.

    climate change Noun

    gradual changes in all the interconnected weather elements on our planet.

    Encyclopedic Entry: climate change
    cloud Noun

    visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

    Encyclopedic Entry: cloud
    coal Noun

    dark, solid fossil fuel mined from the earth.

    Coal Oil Point Noun

    place in the Pacific Ocean off the coast of the U.S. state of California that naturally emits gases such as methane; a seep field.

    coast Noun

    edge of land along the sea or other large body of water.

    Encyclopedic Entry: coast
    combat Verb

    to fight.

    concentration Noun

    measure of the amount of a substance or grouping in a specific place.

    consume Verb

    to use up.

    contaminate Verb

    to poison or make hazardous.

    coolant Noun

    substance, usually a liquid or gas, that reduces the temperature of a system or piece of machinery.

    coral Noun

    tiny ocean animal, some of which secrete calcium carbonate to form reefs.

    crater Noun

    bowl-shaped depression formed by a volcanic eruption or impact of a meteorite.

    Encyclopedic Entry: crater
    crop Noun

    agricultural produce.

    Encyclopedic Entry: crop
    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    Encyclopedic Entry: current
    cyanobacteria Noun

    type of aquatic bacteria that can photosynthesize light to create energy. Also called blue-green algae (even though it is not algae) and (in freshwater habitats) pond scum.

    DDT Noun

    (dichloro-diphenyl-trichloroethane) toxic chemical used as an insecticide but illegal for most uses in the U.S. since 1972.

    dead lake Noun

    body of water where fish or other aquatic organisms no longer live beneath the surface due to natural or manmade pollution.

    dead zone Noun

    area of low oxygen in a body of water.

    Encyclopedic Entry: dead zone
    decade Noun

    10 years.

    decompose Verb

    to decay or break down.

    Deepwater Horizon Noun

    oil rig in the Gulf of Mexico that exploded in 2010.

    descend Verb

    to go from a higher to a lower place.

    devastate Verb

    to destroy.

    developing world Noun

    nations with low per-capita income, little infrastructure, and a small middle class.

    discourage Verb

    to disapprove or encourage someone not to do something.

    dispose Verb

    to throw away or get rid of.

    drab Adjective

    dull or boring.

    drill Verb

    to make a hole using a rotating digging tool.

    drought Noun

    period of greatly reduced precipitation.

    Encyclopedic Entry: drought
    Earth Noun

    our planet, the third from the Sun. The Earth is the only place in the known universe that supports life.

    Encyclopedic Entry: Earth
    economic Adjective

    having to do with money.

    eject Verb

    to get rid of or throw out.

    electricity Noun

    set of physical phenomena associated with the presence and flow of electric charge.

    environment Noun

    conditions that surround and influence an organism or community.

    erupt Verb

    to explode or suddenly eject material.

    exhaust Noun

    gases and particles expelled from an engine.

    expel Verb

    to eject or force out.

    factory Noun

    one or more buildings used for the manufacture of a product.

    fertilizer Noun

    nutrient-rich chemical substance (natural or manmade) applied to soil to encourage plant growth.

    fine Verb

    to punish, usually by charging an economic penalty or fee. Or, the penalty or fee itself.

    fishery Noun

    industry or occupation of harvesting fish, either in the wild or through aquaculture.

    flood Noun

    overflow of a body of water onto land.

    Encyclopedic Entry: flood
    fog Noun

    clouds at ground level.

    Encyclopedic Entry: fog
    food Noun

    material, usually of plant or animal origin, that living organisms use to obtain nutrients.

    Encyclopedic Entry: food
    food web Noun

    all related food chains in an ecosystem. Also called a food cycle.

    Encyclopedic Entry: food web
    forest Noun

    ecosystem filled with trees and underbrush.

    fossil fuel Noun

    coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.

    gasoline Noun

    liquid mixture made from oil and used to run many motor vehicles.

    generate Verb

    to create or begin.

    glacier Noun

    mass of ice that moves slowly over land.

    Encyclopedic Entry: glacier
    gleam Verb

    to shine brightly.

    global warming Noun

    increase in the average temperature of the Earth's air and oceans.

    Encyclopedic Entry: global warming
    government Noun

    system or order of a nation, state, or other political unit.

    gravestone Noun

    stone marking a person's burial place, often engraved with the person's name and dates of birth and death.

    Great Pacific Garbage Patch Noun

    area of the North Pacific Ocean where currents have trapped huge amounts of debris, mostly plastics.

    Encyclopedic Entry: Great Pacific Garbage Patch
    greenhouse effect Noun

    phenomenon where gases allow sunlight to enter Earth's atmosphere but make it difficult for heat to escape.

    Encyclopedic Entry: greenhouse effect
    greenhouse gas Noun

    gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.

    groundwater Noun

    water found in an aquifer.

    Encyclopedic Entry: groundwater
    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    harmful Adjective

    damaging.

    harmful algal bloom (HAB) Noun

    rapid growth of algae that can threaten an aquatic environment by reducing the amount of oxygen in the water, blocking sunlight, or releasing toxic chemicals.

    harvest Noun

    the gathering and collection of crops, including both plants and animals.

    hazard Noun

    danger or risk.

    haze Noun

    group of solid and liquid particles in the air that makes it difficult to see.

    heavy metal Noun

    chemical substance with a specific gravity of at least 5.0.

    herbivore Noun

    organism that eats mainly plants.

    Encyclopedic Entry: herbivore
    hydrocarbon Noun

    chemical compound made entirely of the elements hydrogen and carbon.

    hygiene Noun

    science and methods of keeping clean and healthy.

    ice sheet Noun

    thick layer of glacial ice that covers a large area of land.

    Encyclopedic Entry: ice sheet
    incinerate Verb

    to burn up entirely.

    industry Noun

    activity that produces goods and services.

    inefficient Adjective

    not able to perform a task well.

    infertile Adjective

    unproductive or barren.

    ink Noun

    dark liquid used for printing or artwork.

    invest Verb

    to contribute time or money.

    invisible Adjective

    unable to be seen.

    island Noun

    body of land surrounded by water.

    Encyclopedic Entry: island
    issue Verb

    to distribute, give away, or sell.

    jet stream Noun

    winds speeding through the upper atmosphere.

    Encyclopedic Entry: jet stream
    Krakatoa Noun

    island in Indonesia, site of major volcanic eruption in 1883. Also called Krakatau.

    Kyoto Protocol Noun

    (1997) international agreement to reduce greenhouse gas emissions.

    lake Noun

    body of water surrounded by land.

    landfill Noun

    site where garbage is layered with dirt and other absorbing material to prevent contamination of the surrounding land or water.

    land pollution Noun

    introduction of harmful materials into the surface environment.

    landscape Noun

    the geographic features of a region.

    Encyclopedic Entry: landscape
    landslide Noun

    the fall of rocks, soil, and other materials from a mountain, hill, or slope.

    Encyclopedic Entry: landslide
    lava Noun

    molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

    law Noun

    public rule.

    leech Noun

    carnivorous or bloodsucking worm.

    Love Canal Noun

    New York town and the site of a former toxic waste dump.

    lung Noun

    organ in an animal that is necessary for breathing.

    malaria Noun

    infectious disease caused by a parasite carried by mosquitoes.

    mar Verb

    to spoil or damage.

    marble Noun

    type of metamorphic rock.

    marine Adjective

    having to do with the ocean.

    marsh Noun

    wetland area usually covered by a shallow layer of seawater or freshwater.

    Encyclopedic Entry: marsh
    massive Adjective

    very large or heavy.

    meteorologist Noun

    person who studies patterns and changes in Earth's atmosphere.

    methane Noun

    chemical compound that is the basic ingredient of natural gas.

    microbe Noun

    tiny organism, usually a bacterium.

    microscopic Adjective

    very small.

    mine Verb

    to extract minerals from the Earth.

    mining Noun

    process of extracting ore from the Earth.

    monument Noun

    large structure representing an event, idea, or person.

    nation Noun

    political unit made of people who share a common territory.

    Encyclopedic Entry: nation
    natural disaster Noun

    an event occurring naturally that has large-scale effects on the environment and people, such as a volcano, earthquake, or hurricane.

    natural gas Noun

    type of fossil fuel made up mostly of the gas methane.

    Encyclopedic Entry: natural gas
    nitrogen Noun

    chemical element with the symbol N, whose gas form is 78% of the Earth's atmosphere.

    nitrogen oxide Noun

    one of many chemical compounds made of different combinations of nitrogen and oxygen.

    Nobel Prize Noun

    one of five awards established by the Swedish businessman Alfred Nobel in 1901. Nobel Prizes are awarded in physics, chemistry, medicine, literature, and peace.

    nuclear reactor Noun

    machinery that controls a nuclear reaction, usually for the production of electricity.

    nutrient Noun

    substance an organism needs for energy, growth, and life.

    Encyclopedic Entry: nutrient
    ocean acidification Noun

    decrease in the ocean's pH levels, caused primarily by increased carbon dioxide. Ocean acidification threatens corals and shellfish.

    oil Noun

    fossil fuel formed from the remains of marine plants and animals. Also known as petroleum or crude oil.

    oil rig Noun

    complex series of machinery and systems used to drill for oil on land.

    oil slick Noun

    smooth, dark coating on the surface of a body of water caused by an oil spill or leak.

    oil spill Noun

    accidental release of petroleum products into a body of water, either by an oil tanker or an offshore oil rig.

    ozone hole Noun

    circular pattern, usually located near the Antarctic, of thin atmospheric ozone, which absorbs harmful ultraviolet sunlight.

    ozone layer Noun

    layer in the atmosphere containing the gas ozone, which absorbs most of the sun's ultraviolet radiation.

    Encyclopedic Entry: ozone layer
    particle Noun

    small piece of material.

    Paul Hermann Muller Noun

    (1899-1965) Swiss chemist and businessman.

    pelican Noun

    large marine bird with a big bill.

    permanent Adjective

    constant or lasting forever.

    pesticide Noun

    natural or manufactured substance used to kill organisms that threaten agriculture or are undesirable. Pesticides can be fungicides (which kill harmful fungi), insecticides (which kill harmful insects), herbicides (which kill harmful plants), or rodenticides (which kill harmful rodents.)

    petroleum Noun

    fossil fuel formed from the remains of ancient organisms. Also called crude oil.

    petroleum seep Noun

    place where oil or natural gas from the Earth's interior leaks to the surface naturally.

    phenomenon Noun

    an unusual act or occurrence.

    phosphorus Noun

    chemical element with the symbol P.

    plastic Noun

    chemical material that can be easily shaped when heated to a high temperature.

    plume Noun

    single, upward flow of a fluid, such as water or smoke.

    poison Noun

    substance that harms health.

    pollutant Noun

    chemical or other substance that harms a natural resource.

    pollution Noun

    introduction of harmful materials into the environment.

    Encyclopedic Entry: pollution
    power plant Noun

    industrial facility for the generation of electric energy.

    predator Noun

    animal that hunts other animals for food.

    Rachel Carson Noun

    (1907-1964) American biologist and author.

    radioactive Adjective

    having unstable atomic nuclei and emitting subatomic particles and radiation.

    rain Noun

    liquid precipitation.

    Encyclopedic Entry: rain
    recycle Verb

    to clean or process in order to make suitable for reuse.

    reduce Verb

    to lower or lessen.

    region Noun

    any area on the Earth with one or more common characteristics. Regions are the basic units of geography.

    Encyclopedic Entry: region
    remote Adjective

    distant or far away.

    resource Noun

    available supply of materials, goods, or services. Resources can be natural or human.

    reuse Verb

    to use again.

    rock Noun

    natural substance composed of solid mineral matter.

    runoff Noun

    overflow of fluid from a farm or industrial factory.

    Encyclopedic Entry: runoff
    sand Noun

    small, loose grains of disintegrated rocks.

    sea ice Noun

    frozen ocean water.

    sea level Noun

    base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

    Encyclopedic Entry: sea level
    seep Verb

    to slowly flow through a border.

    seldom Adverb

    not very often.

    sewage Noun

    liquid and solid waste material from homes and businesses.

    sewage treatment Noun

    process of removing harmful pollutants and contaminants from water discarded by homes and businesses, so the water is safe for most uses.

    Silent Spring Noun

    (1962) nonfiction book by Rachel Carson that documented the consequences of a polluted environment, especially the use of the pesticide DDT.

    smog Noun

    type of air pollution common in manufacturing areas or areas with high traffic.

    Encyclopedic Entry: smog
    smoke Noun

    gases given off by a burning substance.

    soil Noun

    top layer of the Earth's surface where plants can grow.

    spew Verb

    to eject or discharge violently.

    stone Noun

    piece of rock.

    storm Noun

    severe weather indicating a disturbed state of the atmosphere resulting from uplifted air.

    storm drain Noun

    system to empty streets of excess rainwater. Storm drains flow into local creeks, rivers, or seas.

    stream Noun

    body of flowing water.

    Encyclopedic Entry: stream
    strenuous Adjective

    energetic or requiring a lot of activity.

    sulfur Noun

    chemical element with the symbol S.

    sulfur dioxide Noun

    greenhouse gas that can cause acid rain.

    sulfuric acid Noun

    toxic chemical made of hydrogen, sulfur, and oxygen.

    Superfund Noun

    federal program to clean up hazardous waste sites in the U.S. Also called the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA).

    survive Verb

    to live.

    Taj Mahal Noun

    (1632) large, white mausoleum complex in Agra, India, built by Shah Jahan for his wife Mumtaz.

    tar ball Noun

    small, sticky piece of tar emitted by a natural or manmade oil spill that floats in the ocean and often washes up on beaches.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    tide Noun

    rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

    Encyclopedic Entry: tide
    tourism Noun

    the industry (including food, hotels, and entertainment) of traveling for pleasure.

    toxic Adjective

    poisonous.

    traffic Noun

    movement of many things, often vehicles, in a specific area.

    tree Noun

    type of large plant with a thick trunk and branches.

    twine Noun

    strong thread made from at least two strings twisted together, often made of plastic.

    ultraviolet radiation Noun

    powerful light waves that are too short for humans to see, but can penetrate Earth's atmosphere. Ultraviolet is often shortened to UV.

    United Nations Noun

    international organization that works for peace, security and cooperation.

    urban area Noun

    developed, densely populated area where most inhabitants have nonagricultural jobs.

    Encyclopedic Entry: urban area
    valley Noun

    depression in the Earth between hills.

    vast Adjective

    huge and spread out.

    visible Adjective

    able to be seen.

    volcanic ash Noun

    fragments of lava less than 2 millimeters across.

    Encyclopedic Entry: volcanic ash
    volcanic gas Noun

    gas such as water vapor or carbon dioxide that is released into the atmosphere by a volcano.

    volcano Noun

    an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

    Encyclopedic Entry: volcano
    water pollution Noun

    introduction of harmful materials into a body of water.

    waterway Noun

    body of water that serves as a route for transportation.

    wetland Noun

    area of land covered by shallow water or saturated by water.

    Encyclopedic Entry: wetland
    wildlife Noun

    organisms living in a natural environment.

    wind Noun

    movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

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