UnderstandingGeologic Time
How old is it? How do we know?
•Absolute dating – process of assigning aprecise numerical age to an organism, objector event
•Relative dating – process of placing objects orevents in sequence (first, second, third…)
Uniformitarianism
•James Hutton proposed that laws of natureoperate today as they did in the past (takealong time)
–Mountain building
–Erosion
–Sediment deposition and lithification to rocks
Principles of Relative Dating
•Original horizontality – sediments aredeposited in layers, oldest on the bottom.
•Overlapping features – (cross cutting) if a rockor fault cuts across a rock layer it must beyounger than what it cuts across.
•Unconformities – gaps in the rock recordwhere erosion destroys “time” or depositionof new rock does not occur.
Sequence One
Sequence Two
Fossils
•Remains or traces of organisms found in therock record (usually SEDIMENTARY rocks)
–Correlation – matching fossils/rocks in one areawith those in another (if B follows A in all places Ais younger than B)
–Index fossil – evidence of organisms that livedover a large area but for a short period of time
How has animal life changed?
How has plant life changed?
Geologic Time Scale
•History of Earth as evidenced by fossils foundin the rock record, boundaries determined by:
–Catastrophic geological events
–Major environmental changes
–Extinction and explosion of new life (change infossils)
Absolute Dating
•Some minerals in IGNEOUS rocks areradioactive and decay in predictable ways (halflife)
•Comparison of isotopes for the ‘parent’ and‘daughter’ atoms provide a numerical “age”
Historical Extinction Events
Has a new Geologic epochalready begun?
Think about why scientists name anew time period.
Epoch
Anthropocence – Age of Man?
Anthropocene?
