miércoles, 20 de abril de 2011

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.


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