1. abrasion
   growth
2. iceberg

The term abrasion means erosion by friction. Abrasion is how rocks are ground down.

1. dew
   lava
2. dust

Water that has condensed on a cool surface overnight is called dew. The temperature at which dew forms is called the dew point.

1. top
   end
2. core

The center of an object is its core. The earth's core is made of iron and nickel.

1. Cretaceous
   old
2. ancient

The third period of the Mesozoic era was the Cretaceous period. The Cretaceous period began approximately 144 million years ago.

1. avalanche
   cyclone
2. eruption

A cyclone is a violent storm in which air moves in a circular direction. Anticyclones revolve opposite the Earth's rotation.

1. aluminum
   carbon
2. base

Aluminum is a silvery ductile metallic element. Bauxite is made up partly of aluminum.

1. anemometer
   barometer
2. thermometer

An anemometer is a gauge for recording the speed and direction of wind. A barometer measures air pressure.

1. anticline
   billow
2. cyclone

Anticline is a fold in a rock that resembles an arch. The fold is arched upward.

1. well
   aquifer
2. hole

An aquifer is underground layer of rock or sand that yields groundwater. Aquifers can be tapped for wells and springs.

1. gold
   silver
2. argon

Argon is a colorless and odorless inert gas. The symbol of argon is "A."

1. crust
   mantle
2. atmosphere

An atmosphere is the envelope of gases surrounding any celestial body. The earth has an atmosphere.

1. sea
   ocean
2. atoll

An atoll is an island consisting of a coral reef surrounding a lagoon. The reef of an atoll is circular.

1. atom
   cell
2. nucleus

The smallest component of an element is an atom. Atoms are linked by chemical bonds.

1. atmosphere
   aurora
2. crust

Bands of light caused by charged solar particles are called auroras. The Northern Lights are an aurora.

1. tornado
   cyclone
2. cirrus

A wispy white cloud at a high altitude is a cirrus cloud. Cirrus clouds are made up of ice crystals.

1. climate
   rain
2. snow

The weather in some location averaged over a period of time is called climate. Climate is a factor in a biome.

1. volcano
   lava
2. avalanche

A slide of large masses of snow, ice and mud down a mountain is an avalanche. Gravity is the force that causes an avalanche.

1. coast
   mountain
2. volcano

The shore of a sea or ocean is called a coast. We had to throw in a really easy one, right?

1. volcano
   ocean
2. cavern

A large cave or a large chamber in a cave is a cavern. Caverns are typically found underground.

1. atmosphere
   bedrock
2. volcano

Solid unweathered rock beneath surface deposits of soil is called bedrock. The Flintstones lived in the town of Bedrock ... oops, that's a different quiz.

1. biome
   jungle
2. desert

A biome is major ecological community with distinct climate and flora. A rainforest is a biome.

1. mountain
   continent
2. peak

One of the large landmasses of the earth is a continent. There are seven continents on earth.

1. precipice
   temperate
2. absolute zero

The lowest temperature theoretically attainable is defined by the term absolute zero. This is the temperature at which, theoretically, no molecular activity exists.

1. pebble
   cobble
2. boulder

A boulder is a large smooth mass of rock detached from a place of origin. In order of size: pebble, cobble, boulder.

1. aggregate
   acid
2. base

Aggregate is defined as a sum total of many heterogeneous things taken together. It also describes a type of rock.

1. butte
   mountain
2. jetty

A butte is a hill that rises abruptly from the surrounding region. A butte and a mesa are not the same thing.

1. caldera
   lava
2. flow

A caldera is a large crater caused by the violent explosion of a volcano. The crater is depressed and circular.

1. boron
   gold
2. carbon

Carbon is an abundant nonmetallic element in all organic compounds. The symbol for carbon is "C."

1. base rain
   precipitation
2. acid rain

Acid rain is defined as precipitation forming when gas emissions combine with water. Acid rain is bad for the environment.

1. oxygen
   carbon dioxide
2. cyanide

Carbon dioxide is a heavy, odorless, colorless gas formed during respiration and by the decomposition of organic substances. Plants absorb carbon dioxide.

1. condensation
   lava
2. butte

Condensation is process of changing from a gas to a liquid or solid state. Clouds are the result of condensation.

1. absorb
   repel
2. react

Absorb means to take in liquid. Light can also be absorbed.

1. growth
   sprout
2. decay

Decay is the organic phenomenon of rotting. Decay is a factor in absolute dating.

1. base
   acid
2. gas

Any of various water-soluble compounds having a sour taste is the definition of an acid. This term is also used in chemistry.

1. ground level
   altitude
2. mountain

Altitude is defined as elevation above sea level or above the earth's surface. An altimeter is used to measure altitude.