Earth’s Geological History
Geological TimeScale
What does this tellyou?
What do the breaksrepresent?
Index Fossils
What are they?
Found in a narrow time range but was widely distributedaround the earth
Used to date rock layers
example: trilobite
Unconformity
Gaps in the rock record
Types
–Angular-older layers dip at a different angle thenthe younger layers
–Disconformity-rock layers are parallel
–Nonconformity (heterolithic)- younger rock restnonparallel to older rock layers
–Local unconformity-stritcly limited and representsa short period
Absolute Dating vs. Relative Dating
Absolute-
–Any method of measuring the age of an event orobject in years
Actual age for a rock or mineral
Relative-
–Uses information about rock layers and the fossilrecord to determine the age relationshipsbetween rocks
Putting layers in order
Absolute Methods
Radiometric dating uses Radioactive decay
–Process in which a radioactive isotope tends tobreak down into a stable isotope of the sameelement or another element
REMEMBER isotope-atom with same number of protonsas other atoms of same element but different amount ofnuetrons (different mass)
Half-life- amount of time needed for half of the sample todecay
Relative Dating Methods
Law of Superposition
–Oldest rocks lie on thebottom and the youngestrocks are on top of anyundisturbed sequence ofsedimentary rocks
Plate Tectonics
The theory that explains how large pieces of theearth’s outermost layer called tectonic plates moveand change shape.
–Explained by the theory of continental drift: gradual shiftingof earth’s plates causes continents to change their globalpositions over time.
Evidence:
–Fossil record
–Matching coastlines
–Index fossils
Plate Boundaries
Divergent Boundary- Where two plates aremoving apart
–Evidence
Deep ocean trenches
Convergent Boundary- Where two plates aremoving together
–Evidence
Mountain Ranges