Transcript RELATIVE AND ABSOLUTE DATING

RELATIVE AND
ABSOLUTE DATING
Ashley Allen
Oneonta High School
Alabama Paleontological Society
Objectives
Distinguish between absolute dating
and relative dating.
Review law of superposition.
Discuss the importance of half-life and
radioactive decay.
Conduct activity on relative and
absolute dating.
Two Ways to Skin a Cat
Relative dating of fossils is a system in which a fossil
is given an age designation in terms of epoch, period,
or era which can be compared to other geologic units
of time as older or younger, but without the burden of
assigning a specific number.
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For example, a Pennsylvanian lycopod bark impression is
older than a Cretaceous oyster and younger than a
Mississippian brachiopod
Relative dating is best explained when covering the law of
superposition and a geologic time scale
Absolute dating of a fossil involves assigning a
specific quantity of age with a fossil such as saying
that an echinoid, Hardouinia bassleri, is 83 million
years old.
Two Inescapable Laws
The law of superposition states that older
sedimentary rocks were deposited prior to
younger sedimentary rocks, therefore, as one
ascends a rock face with multiple formations,
the oldest rock layer is on the bottom and the
rock units get progressively younger as one
ascends the exposure.
The law of faunal succession states that as
one views progressively older fossils, they
become more and more dissimilar with
modern forms of life with which we are most
familiar.
Law of Superposition
Law of Faunal
Succession
Note the general
appearance of more
familiar species the
closer one gets to the
present time.
Radioactive Decay
Unstable parent radioactive isotopes decay at
a stable rate which cannot be altered.
Each type of radioactive parent isotope has a
unique half-life.
A half-life is the amount of time that it takes
for half of the given radioactive parent isotope
to decay into a stable daughter product.
By comparing the amount of radioactive
parent isotope in remains to the stable
daughter product, an absolute age may be
determined.
Carbon Dating
Web Resources
Many radiometric dating activities may be
found by going to
http://www.kn.pacbell.com/wired/fil/ or by
typing filamentality into any search engine.
At the core of each activity is the concept of
half-life.
Technology will limit the amount of detectable
radioactive parent isotope or stable daughter
product.
References
Law of Superposition http://www.calstatela.edu/faculty/acolvil/geotime/gran
dcanyon_strat.jpg
Law of Faunal Succession http://mpschmidt.homestead.com/files/GeoTimeScale
.jpg
Carbon Dating http://ttevisual.com/physics/images/file5/dkph5.093_212.jpg
Carbon Dating Shell - http://www.fmi.unisofia.bg/fmi/contmech/kmarkov/history/gifs/carbon.gif