Chronology and time scales Flashcards
(33 cards)
Relative ages
Based upon order of formation
Qualitative
Absolute ages
Actual number of years since event
Quantitative
Tools for determining relative age
uniformatization ,superposition, original horizontality, continuity, cross cutting relationships, inclusions, baked contact
Uniformitarionism
The present is key to the past
Horizontality and continuity
settle out of fluid by gravity
settle horizontally
Superposition
an undeformed sequence of layered rocks
Each bed is older than the one above
Three types of unconformity (3)
Angular unconformity
non-conformity
disconformity
Angular unconformity
deformed by orgogenesis
Mountains eroded completely away Renewed marine invasion
New sediments deposited
Non-conformity
igneous/metamorphic rocks capped by sandstone
Disconformity
parallel strata bounding nondeposition
interruption by sediment
pause in deposition
sea level pauses
fossil range
first and last appearance
fossil correlate strata
1) Regional
2) Globally
3) locally
Types of stratiographic correlations (2)
- Lithologic correlation
2. Fossil correlation
Lithologic correlation
Regional
sequence - in the order the rocks occur
Fossil correlation
Based on fossils within the rocks
Eons
largest subdivision
hundreds to thousands of years
Eras
subdivisions of an eon
65 - hundreds Ma
Periods
Divisions of an era
2-70 Ma
Epochs
divisions of a period
.011 - 22 MA
Time classifications
Eon : largest
Era
Period
Epochs : Smallest
Names of Eons (4)
Phanerozoic
Proterozoic
Archean
Hadean
Phanerozoic
visible life” (542 Ma to present)
appearance of hard shells
diversity quickly over time
Proterozoic
” before life” (2.5-0.542 Ga)
build up of O2
increased photosynthetic organisms
plate boundary formations
Archean
“ancient” (3.8 to 2.5 Ga)
birth of continents
earliest forms of life
