Earth – Vocabulary for Children

air  The mixture of gases that forms the earth’s atmosphere.

air pressure  The weight of air pressing on the earth; at sea level, about 14.7 pounds per square inch.

angle of repose  The greatest angle at which rocks, sand, or other material can remain without sliding.

anvil bone  The tiny bone in our middle ear, shaped like an anvil, that conducts sound waves to the stirrup bone.

auditory nerve  The nerve leading from the inner ear to the brain that allows us to hear different sounds.

axis  An imaginary line through the earth’s poles, around which it rotates; the earth’s axis is tilted 23.5° with respect to the sun.

base plate  A rectangular plate on which the orienteering compass housing is mounted, that shows markings including the direction of travel arrow.

boulder  A rock larger than 10 inches at its widest part.

capillary action  The movement of water inside tiny spaces, even upwards against the force of gravity, caused by the attraction of water molecules to each other and to various other materials.

carbon dioxide  A colorless, odorless gas found in the atmosphere and used by plants for photosynthesis.

 cardinal direction  One of the four main points of a compass – north, east, south, or west.

cirrus  Wispy clouds, often in long curling strands, found above 20,000 feet, made of tiny ice crystals rather than water droplets.

cloud  A mass of tiny water droplets or ice crystals suspended in the air, that looks white or gray and may produce rain or snow.

cobble  A rock larger than 2.5 inches but less than 10 inches at its widest part.

cochlea  A fluid-filled, snail-shaped structure of the inner ear, containing hairs connected to the nerve endings for hearing.

compass  A scientific instrument for finding direction, with a magnetic needle that is attracted to the earth’s magnetic poles.

compass housing  The fluid-filled disk mounted on the base plate of a compass that can be rotated manually, the rim marked with the degrees of a circle (0° to 360°) and with letters for the cardinal directions N, S, E, and W.

compass needle  A thin, magnetized strip of metal suspended on a pivot inside the compass housing that swings freely and points toward the earth’s magnetic poles. The side that points north is red.

condensation  Changing from a gas to a liquid, as when water vapor is cooled and sticks to tiny particles or surfaces, forming water droplets.

contract  To get smaller.

crystals  Solids that have a definite chemical makeup, and a regular and repeated arrangement of their atoms. With space to grow freely they form flat surfaces (facets) that meet at an angle.

cumulonimbus  A towering, dark, heaped-up cumulus cloud that can grow up to 14 miles high, and can produce violent thunderstorms, high winds and hail.

cumulus  A white cloud with puffy heaps and a flat base, found below 6500 feet above the ground, seen on sunny days.

deposition  The settling out and piling up of loose sand,  rocks or other materials transported by agents like wind, water or glaciers.

direction of travel arrow  An arrow on the base plate of an orienteering compass, extending from the rim of the compass housing to the edge of the base plate.

ear  The hearing organ, which can take different forms in different animals.

ear canal  The tube leading from the outer ear to the eardrum and internal parts of the ear.

eardrum  The thin membrane inside the ear canal that vibrates when a sound wave reaches it, transferring the vibration to the bones of the middle ear.

echo  A sound repeated by being reflected from a wall, mountain or other large, hard surface.

energy  Any source of useable power such as solar radiation, fossil fuel, or electricity.

equator  An imaginary line around the middle of the earth, dividing it into northern and southern halves.

erosion  The wearing away and carrying off of rock, soil, sand or other material by agents like wind, water, glaciers.

evaporation  Changing from a liquid to a gas, such as when water that is heated becomes water vapor.

expand  To get larger.

fossil  A remnant or trace of an organism of a past geologic age, such as an imprint or a skeleton or shell turned to stone and preserved in rock.

gas  A state of matter in which molecules are loosely bonded and can spread out to fill any available space.

glacier  A large, long-lasting mass of compacted snow and ice.

gravity  The pull of objects toward each other, like the pull of the Earth that causes things to fall downward, and keeps us on the ground.

groundwater  Water that is in the soil, in rocks and underground.

hammer bone  The tiny hammer-shaped bone in the middle ear that conducts sound waves to the anvil bone.

igneous  Rocks formed from the cooling and hardening of molten magma.

inner ear  The innermost part of the ear that contains the cochlea and the semicircular canals, which are important for balance.

liquid  A state of matter in which molecules are loosely-bonded and can slide past each other; a fluid.

magma  Molten rock found deep inside the earth.

magnetic field  An area of force surrounding a magnet. The Earth has a magnetic field because of currents within its molten metallic core.

mental map  A picture in our mind of where things are located in a place we know well.

metamorphic  Rocks formed when igneous, sedimentary or metamorphic rock is changed by heat and pressure.

middle ear  The space between the eardrum and the inner ear that contains the three tiny bones that conduct  sound waves to the inner ear.

mineral  A naturally-occurring solid with a crystal form, that has a definite chemical makeup and that did not come from a living creature. Examples are quartz, diamond, mica, gold, talc.

navigation  Finding your way; knowing how to travel to a particular place.

orbit  The pathway of one object around another as the Earth’s pathway around the sun.

orientation  Knowing one’s position in relation to the surroundings; knowing where you are in relation to where you want to go.

orienting arrow  Cross-hatching or parallel lines on the compass housing, adjacent to the letter ‘N,’ that is used in setting the compass; also called “bed” or “shed.”

oxygen  Colorless, odorless gas that forms about 21 percent of Earth’s atmosphere and is essential for living things to breathe.

pebble  A rock smaller than 2.5 inches at its widest part, but larger than a grain of sand.

pinna  The outer ear.

pitch  How high or low a tone sounds.

poles  The north and south ends of Earth.

precipitation  Water returning to the earth from the air as rain, snow, sleet, hail or a mixture.

respiration  Breathing; the process of taking in oxygen to supply energy for bodily functioning, releasing carbon dioxide and water as waste products.

revolve  Travel in a path around a central body, as the earth revolving around the sun; orbit.

rotate  Turn on an axis, like a top.

roundness  A measure of how much the edges and corners of rock fragments have been  ground down and smoothed from being transported in streams or glaciers.

seasons  Parts of the year characterized by different weather patterns.

sediment  Particles of sand, gravel, shells or other materials, that are carried and deposited by water, wind or ice.

sedimentary  Rocks formed from the pressing and cementing together  of particles such as clay, sand, rock fragments, or things that were once part of living things like shells and animal skeletons; rocks where fossils can be found.

sense of direction  An awareness of where we are and how to get to another place.

wind sorting  Movement of loose sediments by wind, smaller particles carried farther than larger, heavier ones.

 solid  A state of matter in which the molecules are tightly bonded and cannot move around, but can only vibrate in place.

 sound  Noise; anything we, or other animals, can hear.

 sound wave  Vibration that travels through air, water or solids.

stirrup bone  The tiny bone in our middle ear, shaped like a stirrup, that conducts sound waves to the inner ear.

stratus  A low layer of clouds covering much of the sky on overcast days.

sunlight  Light from the sun; radiation from the sun that we can see.

transpiration  The process of water moving upwards through a plant and being released into the air as water vapor.

vibration  A rapid, repeated, back and forth motion.

water cycle  Continual movement of water from the earth to the atmosphere and back again.

water vapor The gaseous form of water.

wind  Moving air,  mostly in a direction parallel to the ground.

wind direction  The main direction from which a wind is blowing (e.g. a north wind blows from north to south).