DATING AND TIME

BIGGER UNITS OF TIME• What is a millennium?• What is decade?• What is a century?

• How are centuries named?

ACTIVITY

•Complete the Dating Systems activity in your workbook(PDF on the class page)

RELATIVE DATING

Source: http://www.crowcanyon.org/index.php/stratigraphicdating

• Only gives a sequence in relation to other objects

• Is more useful when you know more about surrounding layers and materials

ABSOLUTE DATING•Gives a definite date range for an object• It is the most precise method• It is not reliable on all objects•Objects can be made from materials from earlier time periods (e.g. wood and stone)

ABSOLUTE DATING METHODS •Radio-carbon dating•Dendrochonology•Potassium-Argon dating•Thermoluminescence dating•Amino-acid dating

RADIO-CARBON C-14 DATING

Video: Scientific American Instant Egghead number 28

DENDROCHRONOLOGY•Traditional method for establishing absolute date•Also called Tree Ring Dating•Based on principle that growth rings in some species of tree reflect seasonal and annual rainfall•Good rainfall = large growth ring•Low rainfall = small growth ring•Also uses fire scars

GROWTH RING DATA BASE•Growth ring data collected from many trees in a specific area•Data base of growth rings built up •Growth rings sequences matched to data base

•Trees from the same species, growing in the same area or environment will be exposed to the same conditions, and hence their growth rings will match at the point where their lifecycles overlap.

•Absolute date determined

WEAKNESSES OF DENDROCHRONOLOGY

•Some species do not have distinctive growth rings (especially in tropical areas)

•Wood must be well preserved•There must be an existing master strip in the data base to match up with the wood

ACTIVITY•Complete activities 2 and 3 on the CGS connect page