Water Erosion and Deposition

Runoff

Water that doesn't soak or evaporate but instead flows across Earth's surface.

Channel

Groove created by water moving down the same path.

Sheet Erosion

A type of surface water erosion caused by runoff that occurs when water flowing as sheets picks up sediments and carries them away.

Drainage Basin

Land area from which a river or stream collects runoff.

Meander

Broad, c-shaped curve in a river or stream, formed by erosion of its outer bank.

Groundwater

Water that soaks into the ground and collects in pores and empty spaces.

Permeable

Describes soil and rock with connecting pores through which water can flow.

Impermeable

Describes materials that water cannot pass through.

Aquifer

Layer of permeable rock that allows water to flow through.

Water Table

Upper surface of the zone of saturation.

Spring

Forms when water table meets Earth's surface.

Geyser

Hot spring that erupts periodically and shoots water and steam into the air.

Cave

Underground opening that can form when acidic groundwater dissolves limestone

Longshore Current

Current that runs parallel to the shoreline, is caused by waves colliding with the shore at slight angles, and moves tons of sediment.

Beach

Deposit of sediment whose materials vary in size, color, and composition, and is most commonly found on a smooth, gently sloped shoreline.

Clues to Earth Past

Fossils
The remains, imprints, or traces of prehistoric organisms.

Permineralized remains
Fossils in which the spaces inside are filled with minerals from groundwater.

Carbon Film
A thin film of carbon residue preserved as a fossil

Mold
A type of body fossil that forms in rock when an organism with hard parts is buried, decays or dissolves, and leaves a cavity in the rock.

Cast
A type of body fossil that forms when crystals fill a mold or sediments wash into a mold and harden into rock.

Index Fossils
The remains of species that existed on Earth for relatively short periods of time, were abundant, and were widespread geographically.

Principle of Superposition
States that in undisturbed rock layers, the oldest rocks are on the bottom and the rocks become younger toward the top.

Relative Age
The age of something compared with other things.

Unconformity
A gap in the rock layer that is due to erosion or periods without any deposition.

Absolute Age
Age, in years, of a rock or other object; can be determined by using properties of the atoms that make up materials.

Radioactive Decay
Process in which some isotopes break down into other isotopes and particles.

Half-life
Time it takes for half the atoms of an isotope to decay.

Radiometric Dating

Process used to calculate the absolute age of rock by measuring the ratio of parent isotope to daughter product in a mineral and knowing the half-life of the parent.

Uniformitarianism

Principle stating that Earth processes ocurring today are similar to those that ocurred in the past.