Clues of Earth´s Past

Fossil
 are remains, imprints or traces of prehistoric organism.



 Permialized remains
 are fossils in which the spaces inside are filled with organism from groundwater.



 Carbon film
 a thin film of carbon residue is left, forming a silhoutte of the original organism



 Mold
 the hard part might decay or dissolve, leaving behind a cavity in the rock



 Cast
 mineral rich water or other sediment might enter the cavity, form new rock, and produce a copy of the original form


 Index fossils
 are remains of species that existed on Earth for relative short periods of time, were abundant, and were widespread geographically

 Principle of Superposition
 oldest rocks on the bottom

 Relative age
 something is its age in comparison to other things

 Unconformity
 gaps in rock sequence

 Absolute age
is the age, in years, of a rock or other object

 radioactive decay
the process of breaking down isotopes

 Half life
an isotope is the time it takes half of atoms in the isotope to decay


 Radiometric dating
 the process to decrease as the amount of daughter product increases

 Unconformatism:
process that change the landscape around were slow, and he inferred that they were just slow throught Earth history