martes, 26 de abril de 2011

Clues to Earth's Past

Fossil:

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 left, that forms a silhouette of the original organisms.








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




Cast:
Type of fossil that forms when sediments or water enter the cavity, form new rock, and produce a copy of the original object.




Index fossil: 
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 rock become progressively younger toward the top.




Relative age: 
The age of something compared with other things.




Unconformity: 

Gaps in rock sequences in the rock layer due to erosion or periods without any deposition.




Absolute age:
The age, in years, of a rock or other object.




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




Half-life: 
Time it takes for half of the atoms in the 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 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 evaporates but instead flows across Earth’s surface.



 


 Channel:  
Water moving down the same path that creates a groove.





 Sheet erosion:  
Surface water erosion that occurs when water that is flowing as sheets picks up and carries away sediments.
 



 Drainage basin:  
 The area of land from which a stream or river collects runoff.




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




Groundwater:  
Water that soaks into the ground and collects in pores or empty spaces; an important source of water. 




Permeable: 
Describes rock and material with connecting pores through which water can flow.




Impermeable: 
Describes materials water cannot pass through.




Aquifer:  
The layer of permeable rock that lets water move freely.




Water table:
Upper surface of the zone of saturation; drops during a drought.




Spring:
Occurs when water table meets Earth’s surface, often found on hillsides and used as a freshwater source.




Geyser:
A hot spring that erupts periodically, shooting water and steam into the air.




Cave:
An underground opening that can form when acidic groundwater dissolves limestone.




Longshore current:
Current that runs parallel to the shoreline, is caused by waves colliding against the shore at slight angles, and moves tons of loose sediments.




Beach:
Deposition of sediment that are parallel to the shore.