- FOSSILS:
Fossils are the remains (or other evidence) of life from the geologic past.
Fossil remains are found buried in sediments or in sedimentary rocks.
Scientists who study fossils are called paleontologists.
- Correlation by fossils:
A fossil assemblage is a group of many fossils belonging to several different species.
When paleontologists find the same assemblage of fossils in different places, they conclude
that they are the remains
of species that lived at the same time in those different places.
Rocks containing the same assemblage (or one closely similar) can therefore be judged to be contemporaneous
(of the same time period).
This is called the principle of correlation by fossils.
Correlation by fossils can be used to determine that a rock formation or stratum in one location
is of the same age as another rock formation or stratum far away.
Index fossils are those that are restricted in their time range but widespread geographically.
Wherever they are found, they can be used to identify or confirm the age of a rock formation.
Index fossils commonly found in New York State are shown on pages 8-9 of
this reference chart.
- Regional and world-wide correlation:
Local sequences of sedimentary rocks can be placed into a time sequence using the law of superposition (relative dating).
The principle of correlation allows stratum (part of a local sequence) in one place to be matched to part of a local sequence somewhere else.
By matching as many local sequences as possible, paleontologists and stratigraphers can assemble the world's stratified rocks
into a world-wide sequence.
IMPORTANT NOTE: This is still relative dating, because we have a sequence of older and younger, but no numerical values in years.
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