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
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
