GEOLOGIC TIME

• Concepts of Time
• absolute age: # of years since the rock formed
• relative age: age of sedimentary rock layers in relation to on another


• Relative Dating Techniques
• Stratigraphic Record
• principle of original horizontality
• principle of superposition
• unconformities
• disconformity: erosion removes a part of otherwise undisturbed rock
• angular unconformity: rocks below are at an angle in relation to those above
• nonconformity: sedimentary rocks lie on top of igneous rocks
• principle of cross-cutting relationships
• Fossils (paleontology)
• faunal succession
• formations


• Absolute Time Scale
• Four major time units
• eons
• eras
• periods
• epochs


• Determining absolute time
• radiometric dating
• radioactivity
• half-life

• types
• Rb(87)-Sr(87)
• ½ life = 47 billion
• dating range = 10 mill - 4.6 bill


• Ur(238)-Pb(206)
• ½ life = 4.5 billion
• dating range = 10 mill - 4.6 bill
• K(40)-Ar(40)
• ½ life = 1.3 billion
• dating range = 50,000 - 4.6 bill


• C(14)-N(14)
• ½ life = 5370
• dating range = 100 - 70,000



• Geologic Time Scale



• IMPACT: The earth had not been created through a series of catastrophes, but had instead evolved through the same types of change that can be observed today



• THE PRESENT IS THE KEY TO THE PAST!