are the remains, imprints, or traces of prehistoric organisms.
2. Permineralized remains:
are fossils in which the spaces inside are filled with minerals from groundwater.
3. Carbon film:
a thin film of carbon residue is left, forming a silhouette of the original organism.
4. Mold:
the hard part might decay or dissolve, leaving behind a cavity in the rock.
5. Cast:
a type of body fossil that forms when crystals fill a mold or sediments wash into a mold and harden into rock.
6. Index fossils:
are the remains of species that existed on Earth for relatively short periods of time, were abundant, and were widespread geographically.
7. Principle of superposition:
states that in undisturbed rock layers, the oldest rocks are on the bottom and the rocks become progressively younger toward the top.
8. Relative age:
the age of something compared with the other things.
9. Unconformity:
gap in the rock layer that is due to erosion or periods without any deposition.
10. Absolute age:
is the age, in years, of a rock or other objects.
11. Radioactive decay:
process in which some isotopes break down in other isotopes and particles.
12. Half-life:
time it takes for half of the atoms of an isotope to decay.
13. Radiometric dating:
process used to calculate the absolute age of the rock by measuring the ratio of parent isotope to daughter product in a mineral and knowing the half-life of the parent.
14. Uniformitarianism:
principle stating that Earth processes occurring today are similar to those that occurred in the past.
