Clues to Earth's Past

Fossil Are the remains, imprints, or traces of prehistoric organisms.

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

Carbon film
A silhoutte of the original organism.

Mold
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 fossil
Are 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 progressively younger toward the top.

Relative age
The age of something compared with other things.

Unconformity
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 daugher product in a mineral and knowing the half-life of the parent.

Uniformitarianism
Principle stating that Earth processes occuring today are similar to those that occured in the past.

Water Erosion and Deposition

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

Channel
Grove created by water moving down the same path.

Sheet Erosion
Occurs when water that is flowing as sheet picks up and carries away sediments.

Drainage Basin
Is the area of land from which a stream or river collects runoff.

Meander
The curve grows to become a broad arc.

Groundwater

Water that soaks into the ground collects in these pores and empty spaces and becomes part of.

Permeable

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

Impermeable

Describes materials that water cannot pass through.

Aquifer

A layer of permeable rock that lets water move freely.

Water table

The upper surface of this zone.

Spring

Forms when the water table meets Earth's surface; often found on hillsides and used as a freshwater source.

Geyser

Is a hot spring that erupts periodically, shooting water and steam into the air.

Cave

An underground opening.

Longshore current

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

Beach

Deposits of sediment that are parallel to the shore.