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
Remains or traces of prehistoric life
Fossil
Fossil Requirements
- Rapid burial
- Presence of proactive cover or preserving medium
- Possession of hard parts or durable tissues
Division of the whole geologic history
Geologic time scale (GTS)
Events that happened throughout the Earth’s History
Geologic Time
Eon
Eonothem
Era
Erathem
Period
System
Epoch
Series
Age
Stage
Reference Point of stratigraphic sections of rock defining the lower boundary of Stages on GTS
Global Boundary Stratotype Section and Point
Reference Points on stratigraphic sections of rock defining the boundaries of time units for rock older than 630 million years
Global Standard Stratigraphic Age
Earth and Moon formed
Hadean
Ocean formed, first organisms
Archean
oxygenated atmosphere, multicellular organisms
Proterozoic
