Aim: How do scientists correlate rock strata?
I. Correlation of Rock Strata – geologists try to match
similar rock strata in different locations to see if they
formed at the same time or under similar conditions.
A. Correlation by continuity (“walking the outcrop”)
1. Outcrop – exposed rock layer (bedrock)
2. Follow a rock layer from one end to the next
(horizontally on earth’s surface).
B. Matching Rock Strata
1. Match rock strata in one location to another in a
more distant location. Look for similarities in rock
color, texture, and composition.
2. It is more helpful to match rock layer sequences.
C. Time Correlation
1. Index Fossil – a fossil that can be found over a
large geographic area but existed for a brief period of
geologic time (20 million years).
2. Volcanic Ash Falls – leaves layers of volcanic ash
after a large eruption. Covers a large area with a thin
layer of ash.