Topic 9: Geologic Time
.
Dates to Remember
May 6: Discussion about geologic age and dating (not with each other!). Activity page 425.
May 7: Time line activity - page 427
New words:
Principle of Superposition: oldest rock are below younger rock.
Strata: sedimentary layers
Relative dating: determining the approximate age of rocks by examining their position in the strata.
Index fossil: a fossil that is used to determine the relative age of a strata.
Absolute age: the exact age of a rock
Relative age: the age of a rock compared to other rocks.
Radiometric dating: a measurment of the amount of radioactive elements (e.g. uranium) in a rock.
Half-life: the time it takes to change one element into another e.g. half of uranium changes into lead in 4.5 billion years. Used for very old rocks dating.
Radiocarbon dating: uses carbon-14, which disappears over 50 000 years. Used for younger fossil dating.
Time Scale:
- first microscopic life (3.6 bya)
- first multicellular life (900 mya)
- first oxygen appears in atmosphere (1.9 bya)
- first land plants appear (450 mya)
- formation of the Himalayas begins (30 mya)
- formation of the Atlantic Ocean begins (150 mya)
Eon: largest division of time scale
Era: smaller break up of eon
Period: smaller break up of era
Pangea: supercontinent (around 350 to 180 million years ago)
Gondwanaland and Laurasia: break up of Pangea
Resources: Text Book pages 423-427
- Geologic Time - good presentation
- University of Berkeley site - excellent site on all sorts of geological information.
- Compare geologic time to football field