Relative age and fossils terms

trace fossil

A type of fossil that provides evidence of the activities of ancient organisms

deposition

Process in which sediment is laid down in new locations.

erosion

Processes by which rock, sand, and soil are broken down and carried away

relative age

age of layers in comparison to others

Intrusion

always younger than what it cuts thru

fault

always younger than what it offsets

index fossil

fossils of widely distributed organisms that lived during only one short period. used to identify the ages of rocks.

index fossil

occurs in many locations, lived short period of time, can be used to tell the age of a rock layer (without getting radiometric ages)

law of superposition

oldest at the bottom, youngest at top

crosscutting relationships

states that an igneous intrusion (or fault) is always younger than the rock it cuts across.

absolute age

the real age of a rock layer calculated with radioactive decay

unconformity

time of erosion, much younger in contact with older