How do you know how old it is?

Dating in Geology 1) Relative dating –a) Superposition –b) Correlation 2) Numerical (absolute) dating –radiometrics

Miocene-Pliocene scallops

Paleocene Calcareous Nannoplankton

Permo-Triassic Conodonts

Cretaceous Bivalves

Neogene Calcareous Nannoplankton

Stratigraphic Concepts and Terminology LithostratigraphicGroup Formation Member Bed BiostratigraphicBiozones ChronostratigraphicRocksTime Erathem Era System Period Series Epoch Stage Age

MesozoicCretaceousCenomanian PaleozoicDevonianGivetian CenozoicPaleoceneThanetian 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

IsotopesIsotopes: elements with the same atomic number but different atomic mass (number of neutrons). Some isotopes unstable ( 40 K, 14 C; radioisotopes); others are stable ( 39 K, 41 K, 12 C, 13 C) 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 ParentStable DaughterHalf life Potassium 40 Argon billion yrs Rubidium 87Strontium billion yrs Thorium 232Lead billion years Uranium 235Lead million years Uranium 238Lead billion years Carbon 14Nitrogen years

Measuring decay in half-lives

ParentDaughterHalf LifeDating Range _________________________________________________________________ Carbon-14Nitrogen ± ,000 ________________________________________________________________________ Potassium-40Argon-40 Calcium billion50, billion ________________________________________________________________________ Uranium-238 Lead billion 10 million-4.6 billion Uranium-235 Lead million Uranium-232 Lead billion ________________________________________________________________________ Rubidium-87Strontium-8747 billion10 million-4.6 billion

Minerals you can date Potassium 40 is found in: potassium feldspar (orthoclase) muscovite amphibole glauconite amphibole orthoclase muscovite glauconite

Minerals you can date Uranium may be found in: zircon

Combining Radiometric and Paleontological Dating

Dating in Geology 1) Relative dating –a) Superposition –b) Correlation 2) Numerical (absolute) dating –radiometrics

Dating in Geology 1) Relative dating –a) Superposition –b) Correlation 2) Numerical (absolute) dating –radiometrics