how do you know how old it is?. dating in geology 1) relative dating –a) superposition –b)...
TRANSCRIPT
“How do you know how old it is?”
Dating in Geology
• 1) Relative dating– a) Superposition– b) Correlation
• 2) Numerical (“absolute”) dating
– radiometrics
Miocene-Pliocenescallops
PaleoceneCalcareousNannoplankton
Permo-TriassicConodonts
Cretaceous Bivalves
Neogene Calcareous Nannoplankton
http://www.priweb.org/ed/ICTHOL/timescale.htm
Stratigraphic Concepts and Terminology
Lithostratigraphic Group Formation Member Bed
Biostratigraphic Biozones
Chronostratigraphic Rocks TimeErathem Era System Period Series Epoch Stage Age
Mesozoic Cretaceous Cenomanian
Paleozoic Devonian Givetian
Cenozoic Paleocene Thanetian
Using Index Fossils
Dating in Geology
• 1) Relative dating– a) Superposition– b) Correlation
• 2) Numerical (“absolute”) dating
– radiometrics
Radiometric Dating: the basic idea
• A product is detectable
• The rate of production of that product is known
• Product amount is 0 (or known) at age 0 of sample
• Product / Rate = Time– example: 10g / 0.5g/yr = 20 years
Isotopes: elements with the same atomic number but
different atomic mass (number of neutrons).
Some isotopes unstable (40K, 14C; radioisotopes);
others are stable (39K, 41K, 12C, 13C)
Unstable isotopes (parent) decay to another stable
or unstable isotope (daughter)
Rate expressed as half-life -- time in which ½ of
radioisotopes decay.
Half Lives for Radioactive Elements
Radioactive Parent Stable Daughter Half life
Potassium 40 Argon 40 1.25 billion yrs
Rubidium 87 Strontium 87 48.8 billion yrs
Thorium 232 Lead 208 14 billion years
Uranium 235 Lead 207 704 million years
Uranium 238 Lead 206 4.47 billion years
Carbon 14 Nitrogen 14 5730 years
Measuring decay in half-lives
Measuring decay in half-lives
Parent Daughter Half Life Dating Range
_________________________________________________________________
Carbon-14 Nitrogen-14 5730±30 0100-70,000
________________________________________________________________________
Potassium-40 Argon-40
Calcium-40 1.3 billion 50,000-4.6 billion________________________________________________________________________
Uranium-238 Lead-206 4.5 billion 10 million-4.6 billion
Uranium-235 Lead-207 710 million Uranium-232 Lead-208 14 billion
________________________________________________________________________
Rubidium-87 Strontium-87 47 billion 10 million-4.6 billion
Minerals you can datePotassium 40 is found in:
potassium feldspar (orthoclase)
muscovite
amphibole
glauconite
amphibole
orthoclase
muscovite
glauconite
Minerals you can date
Uranium may be found in:
zircon
zircon
Combining Radiometric and Paleontological Dating
Dating in Geology
• 1) Relative dating– a) Superposition– b) Correlation
• 2) Numerical (“absolute”) dating
– radiometrics
http://www.priweb.org/ed/ICTHOL/timescale.htm
Dating in Geology
• 1) Relative dating– a) Superposition– b) Correlation
• 2) Numerical (“absolute”) dating
– radiometrics