aquifer: Aquifers are places underground through which water flows, like sand, gravel, or even clay. People drill wells hoping to hit an aquifer for a good course of water.

atmosphere: The atmosphere is the pocket of gases surrounding Earth and held in place by gravity.

benthic zone: The benthic zone is the very bottom layer of the ocean.

biodiversity: Biodiversity is how many different kinds of plants and animals there are in one place. The rainforest is famous for its biodiversity because it has so many different species and a lot of them haven't even been discovered yet.

biofuels: Biofuels are fuels made from plants and animals. These fuels are usually used for transportation.

bioluminescence: Bioluminescence is when an animal, like a firefly or deep sea fish, gives off its own light.

biomass: Biomass is the amount of any plant or animal matter that grows and can be used to make energy.

botanist: A botanist is someone who studies plants.

carnivores: Carnivores are meat-eating animals. Carnivores can also refer to the order of mammals that contain bears, wolves, cats, weasels, seals, etc.

climate change: Climate change is a term used by scientists to describe a real change from one climatic type to another.

condensation: Condensation is when water vapor cools and changes back into its liquid form.

Continental Drift Theory: Continental Drift Theory is the theory that the continents have drifted apart and are still in motion today.

decomposers:Decomposers are organisms that break down organic matter, like dead animals or plants.

deforestation: Deforestation is when trees are stripped from the forest.

dodo: Dodos were flightless birds that lived on an isolated island off the coast of Africa. When sailors finally found the island in the 1600s, it took only 80 years for the dodo to go completely extinct.

earth's crust: The earth's crust is the outermost layer of the earth, made up of a series of plates.

ecological footprint: An ecological footprint is the amount that each of us affects the earth by using its resources.

ecotourism: Ecotourism is when people visit a place to see the exotic wildlife and natural habitats. Many countries use ecotourism money to help their economy while protecting their natural habitats.

endangered: A species is considered endangered if there are so few of them that they may soon become extinct.

end-Pleistocene: The end-Pleistocene was a prehistoric time some 15,000 years ago at the end of the geologic time period called the Pleistocene, where a large extinction of many large animals took place.

epipelagic zone: The epipelagic zone is the uppermost layer of the ocean where phytoplankton can get sunlight for photosynthesis.

erg: An erg is a big expanse of shifting sand in the Sahara desert.

estivation: Estivation is when an animal goes into a deep sleep through a very hot time.

evaporation: Evaporation is when water, driven by the heat of the sun, changes into vapor and rises into the air.

extinct: A species becomes extinct when the last one of its kind dies.

fault: A fault is where two of Earth's plates slide past each other. This is an area where earthquakes can occur.

fluorescent lamps:Fluorescent lamps are very special light bulbs that burn cooler and use less energy than regular bulbs.

food web: A food web is the interconnecting food chains of who eats whom in a natural habitat.

fossil record: Fossils are the remains of organisms that lived a long time ago, preserved in the rocks. The fossil record shows us when species went extinct relative to the passage of millions of years.

genes: Genes are the smallest unit of heredity. We have more than 20,000 genes that map out all of our traits from eye color to earlobe shape.

glacier: A glacier is a huge mass of ice made from compacted snow that moves very slowly. They are found in mountainous areas or near the earth's frozen poles.

global warming: Global warming is a term used to describe an increase in the earth's temperature from, in part, humans releasing more carbon dioxide into the air. Scientists believe that will lead to climate change with many negative effects to living things on the planet.

greenhouse effect: The greenhouse effect is when gases in the earth's atmosphere trap heat from the sun and build up, raising the temperature of the earth, acting like a greenhouse.

greenhouse gases: Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone.

groundwater: Groundwater is the water that flows underground filling soil and flowing out into springs and aquifers.

herbivores:Herbivores are plant-eating animals.

hibernation: Hibernation is when an animal spends the cold months of winter in a deep sleep.

ice pack: Ice pack is the thick mass of ice that covers Antarctica, Greenland, and much of the Arctic in winter.

insectivorous: Insectivorous plants are plants that trap and digest insects as added food.

irrigation: Irrigation is when man-made water channels are used to bring in water to grow crops.

keystone species: A keystone species is a species that is so interconnected with the other species in its ecosystem that its disappearance changes the balance of the whole ecosystem.

lithosphere: The lithosphere includes the outer part of the earth — the crust and the mantle.

meteor: A meteor is a rock or other matter that enters our atmosphere from space. Its burning passage toward Earth is called a shooting star.

methane: Methane is a flammable gas that is made when organic matter decomposes. It is a greenhouse gas.

mirage: A mirage looks like water in the distance but is actually shimmering light above a superheated desert plain.

mob of kangaroos: A mob is a group of kangaroos.

oasis: An oasis is a fertile spot in the desert where travelers can find water.

omnivores: Omnivores are animals that eat both meat and plant matter.

order: Order is the classification level where animals are grouped between their class and family. The levels start with kingdom and then progress to phylum, class, order, family, genus, and species. A wolf is in the animal kingdom, chordate phylum, mammal class, carnivore order, canine family, Canis genus, and lupus species.

ozone-depleting gases: Ozone-depleting gases are CFCs, refrigerants, aerosols, solvents, methyl bromide fumigant, and halon.

monoculture: Monoculture is when farmers plant one type of crop only, with no variety.

nocturnal: Nocturnal animals are active at night.

Pangaea: Pangaea was the supercontinent that was made up of all the Earth's continents before they drifted apart 250 million years ago.

peat: Peat develops in wetlands from built-up rotting vegetable matter.

permafrost: Permafrost is the layer of soil just below the surface that stays frozen year-round, mostly in the polar regions of the earth.

pH: Acidity is measured on a pH scale. A pH of 1 is the most acid and a pH of 14 is the most base (or alka-line). Pure water is considered to be neutral. It has a pH of 7. Normal rainwater has a pH of about 6. That is a little acidic because even pure rainwater falls through carbon dioxide in the air. Rain with a pH of less than about 5.3 is considered acid rain. Rain in the northeastern states has a pH between 4 and 5. This is serious acid rain.

photosynthesis: Photosynthesis is the process by which green plants make food from water, carbon dioxide, and the energy of the sun.

photovoltaics: Photovoltaics is how the energy from the sun can be made into usable energy like electricity.

phytoplankton: Phytoplankton are tiny, microscopic plants floating on the top layers of the ocean.

plant transpiration: Plant transpiration is when plants open their pores to take in carbon dioxide for photosynthesis and they lose water to evaporation.

plate tectonics: Plate tectonics describes the plate structure of the earth's crust and how these plates move.

precipitation: Precipitation is when water falls from the sky in the form of rain, snow, hail, sleet, or freezing rain.

producers: The producers are at the bottom of the food chain, making their own food through photosynthesis and providing food for all the herbivores (plant-eating animals).

respiration: Respiration is when a living organism takes in oxygen and releases carbon dioxide to make energy to run its body functions.

satellite: Satellites are objects that orbit around another object, like a planet. We use man-made satellites for many technologies on Earth.

semi-arid: Semi-arid describes habitats that are very dry, with scrubby plants and hardy animals, but are not considered deserts.

semiconductor: A semiconductor is a material that can carry the electrical charge made by sunlight. Most solar semiconductors are a layer of silicon.

sky glow: Sky glow is the light glow in the night sky over cities. It makes viewing the night sky difficult.

slash and burn: Slash and burn is how some people clear forest for farming. It is when all the trees are cut down and then every thing is set on fire to burn away.

smog: Smog is ground level ozone and particulate matter formed by burning fuels on hot, sunny days.

space shuttle: One of the NASA spacecraft we use to reach Earth's orbit on a regular basis.

spawn: Spawn is another word for fish laying their eggs upstream.

sublimation: Sublimation is when ice evaporates directly into vapor without first melting into the water phase.

threatened: When species are not quite endangered but their numbers are low, they are considered threatened.

toxic waste: Toxic waste is trash that can harm or kill living things, including people. Often chemicals, it can be also medical waste.

treaty: A treaty is a signed agreement between two or more countries.

ultraviolet light: Ultraviolet light is a kind of electromagnetic radiation from the sun that has a wavelength shorter than visible light, so we cannot see it. Though too much ultraviolet light is bad for us, we do need some to be healthy.

watt: A watt is a unit of power and how we measure electricity. A regular light bulb usually uses between 40 and 100 watts of electricity. The 100-watt bulb is brighter and uses more units of power.

weather: Weather is what is going on in the atmosphere at any one time in regards to temperature, moisture, wind, and clouds.