miércoles, 27 de abril de 2011

CLUES TO EARTH'S PAST

Fossil 


remains, imprints, or traces of prehistoric organisms that can tell when and were the organisms once lived and how they lived



permineralized remains

fossils in which the spaces inside are filled with minerals from groundwater


carbon film
thin film of carbon residue preserved as a soil


Mold
a type of body fossil that forms in rocks 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
remains of species that existed on earth for relatively short period of time and can be used by geologists to assign the ages of rock

principle of superposition
states that in undisturbed rocks layers, the oldest rock 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 rhe 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


viernes, 25 de marzo de 2011

WATER EROSION AND DEPOSTION

Runoff


 Water that doesn't soak into the ground or evaporates but instead flows across Earth's surface is called runoff.



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; important source of water.

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 though. 


water table
upper surface of the zone of saturation; drops during a drought. 

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


geyser
hot spring taht 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 store at slight angles, and moves tons of loose sediment.

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