Fossils & Geologic Time

Relative Dating
Any method of determining whether an event or object is older or younger than other events or objects.
The idea that younger rocks lie above older rocks in and undisturbed layer.
Absolute Dating
Any method of measuring the age of an event or object in years.
Preserved remains of once-living organisms.
Trace Fossils
Naturally preserved evidence of animal activity. NOT THE REMAINS.
A mark or cavity made in a sedimentary surface by a shell or other body.
They are made by the process called cast replacement. A cast is a three-dimensinal object made when a mold is filled with sediments or minerals and becomes rock, which resemble the decayed item.
Index Fossils
Distict fossils used to compare the relative age of fossils.