Chap 8 Flashcards
Relative age
The sequence in which events took place
Numerical age
the age of events or objects expressed as a number of numbers
Determined using radiometric dating
Also known as absolute age
Contacts
Surfaces seperating successive rock and layers
Formations
Bodies of rock of considerable thickness with recognizeable characteristics allowing them to be distinguished from adjacent rock layers
Principle of original horizontality
Beds of sediment deposited in water formed as horizontal or nearly horizontal layers
Principle of superposition
within sequence of undisturbed sedimentary or volcanic rocks the layers get younger from bottom to top
Principle of lateral continuity
an orignal sedimentary layer extends laterally until it tapers or thins at its edges
Principle of cross cutting relationships
disrupted pattern is older than the cause of disruption
principle of inclusions
fragments embedded in host rock are older than the host rock
Baked contacts
contacts between igneous intrusions and surrounding rocks where surrounding rocks have experienced contact metamorphism
Principle of faunal succession
Fossils appear and disappear in strata in definite and recognizable order due to evolution
Unconformity
A surface or contact that represents a break in the geologic record
1: angular unconformities
2: Disconformities
3: Nonconformities
Angular Unformity
A contact in which younger strata overlies an erosion surface on tilted or golded layered rock
Nonconformity
an unconformity in which an erosional surace on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock
Correlation
determining time equivvalency of rock unites to determine younger or older than another area
1: Lithologic correlation
2: Time correlation (eg index fossil, key bed, unconformities)
Physical continuity
Physically trace continues exposure of a rock unit
Key bed
A very distinct layer, can be used to correlate rocks over great distance E.g. volcanic ash layer
Index fossil
Very shortlived wide spread species known to exist during a specific period of geologic time
Faunal succession
fossil species succeed in one another through the layers in a predictable order
The standard geological time scale
Precambrian - 87% of geologic time
Paleozoic era - Old life, appearance of complex life
Mesozoic era - middle life, dinos abundant,
cenozoic era - new life, mammals and birds abundant
radioactive decay
the spontaneous nuclear change of isotopes with unstable nuclei
Half life
the time it takes for a given amount of a radio active isotope to be reduced by half
