Study Guide – Geology Spring 2007
Name: ______
Relative Sequencing - Geologic PrincipLEs
Principle of Superposition - the older beds are on the bottom, and the younger beds are on the top
Principle of Original Horizontality - sediments are deposited in flat, horizontal layers.
Principle of Lateral Continuity – sediment will be deposited in a layer that extends for a considerable distance laterally, unless pinched out or disrupted.
Principle of faunal Succession – groups of fossil plants or animals occur in the geologic record in a definite and determinable order. A geologic time period can be recognized by it’s fossils.
Principle of Crosscutting Relations – Geologic features, such as faults, and igneous intrusions are younger than the rocks that they cut.
Principle of Inclusion – A rock body that contains inclusions of preexisting rocks is younger than the parent rock that the fragments came from.
Other Time Relationships
Contact metamorphosed zones show the “baked” or super heated contact zone where an igneous body intruded the preexisting (older) rock body.
Unconformities the contact representing missing strata, or a gap in the geologic record
· Disconformity – erosional surface on parallel beds
· Angular unconformity - the contact in which younger strata overlie an erosion surface of tilted of folder layers of rock
· Nonconformity – the contact upon which the erosion surface is on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock.
Geologic Time
Prior to 19th century the accepted age of Earth was based on religious beliefs
James Hutton “father of geology” and Charles Lyell helped to popularize geologic concepts
Standard geologic time Scale – worldwide relative time scale
· Subdivisions based on fossil assemblages
· Divided into eons, eras, periods, epochs and ages
Precambrian – vast amount of time prior to Paleozoic, few fossils preserved
Paleozoic – “old life” , appearance of complex life, many fossil
Mesozoic Era – “middle life” Dinosaurs, era ended by mass extinction
Cenozoic Era – “new Life” Mammals and bird abundant
We are currently in the Holocene Epoch of the Quaternary Period of the Cenozoic Era.
Radiometric dating
· (atomic # = # of protons) (mass # = # of protons and neutrons)
· (Isotopes of an element have the same # of protons but a different # of neutrons)
· Numerical time or absolute time.
· Isotopic dating is the radioactive “clock” that is sealed into newly formed mineral crystals.
· Radioactive decay is the spontaneous nuclear change of isotopes with unstable nuclei.
· The radioisotope is the “parent” and the nuclide is the “daughter”.
· Daughters will decay until they reach stability (a non-radioactive isotope)
· Measuring the rate at which the radioactive elements decay is isotopic dating.
· When radioisotopes decay to form a nuclide, they emit a particle.
· The types of particle emissions
o Alpha emission – ejection of 2 protons and 2 neutrons
o Beta emission – release of an electron from a nucleus
o Electron capture is the third change whereby a proton in the nucleus captures an orbiting electron, the proton becomes a neutron and the atom becomes a different element having an atomic number one less than its parent.
· % of the number of atoms that will decay in a given isotope is constant.
· Rate of decay is expressed as its half-life; the unit name that represents the original parent mass amount decaying to HALF daughter isotope. (50% parent 50% daughter)