Clocks in the Rocks Flashcards
determining age or chronology of events in the history of Earth
Dating
placing rocks in proper sequence of formation without exact time
Relative dating
specify numerical ages of geologic events
Absolute dating
In an undisturbed sequence of strata, each layer (bed) is younger than the layer below and older than the layer above
Law of superposition
Sediments forming strata are originally deposited horizontally. Therefore, any tilted strata must have been horizontal prior to its tilting.
Law of original horizontality
Sediments (therefore strata) are deposited laterally and continuously in all directions unless (1) sediment supply runs out, (2) is impeded by an obstacle, or (3) meets along the edge of the depositional basin
Law of lateral continuity
If one geologic feature cuts across another, the feature that has been cut is older. Conversely, all geologic structure that cuts across another is younger.
Law of cross-cutting relationship
Rock containing inclusions (fragment of another rock) must be younger than the inclusions; inclusions are always older than the rocks that contain them
Inclusions
Fossils contained in rocks succeed each other vertically in a specific, reliable order that can be identified over wide distances
Fossil Succession
Period of erosion, or non-deposition of strata producing a “gap” in the rock record
Unconformity
The strata above and below the unconformity have different dip angles
Angular unconformity
Unconformity between an igneous and/or metamorphic rock overlain by sedimentary strata
Nonconformity
Unconformity between sedimentary strata; both strata above and below are sedimentary
Disconformity
Elements with the same atomic number but a different atomic mass due to different number of neutrons
Isotopes
Change undergone by unstable radioactive isotopes to become more stable
Radioactive decay
