Post on 14-Jun-2015
description
Systems of Dating
Review – Relative Dating
• Typology– computer typology
• Stratigraphy– Try the following examples
Calendars
• Count years• Many different calendars in the world• We use Gregorian calendar• In the European cultures, the year count
based on birth of Christ
Calculating Today’s Date
Gregorian Julian Islamic Hebrew
16 February 2015 AD
3 February 2015 AD
26 Rabi’ath-Thani Shawwal 1436 AH (anno hegirae ‘in the
year of the Hijra’
27 Shevat 5775 AM (anno mundi ‘in the year of the world’)
Mesoamerican calendar.
Birth of Jesus
• AD stands for Anno Domini ‘in the year of our Lord’
• According to Dionysius Exiguus, Jesus was born in AD 1 but most scholars now think it was in fact 6 BC
• The year before Jesus’ birth is 1 BC• System is NOT a mathematical number line• There is no year 0
BCE/CE Dating System
• BCE means Before the Common Era• CE means the Common Era• Numeric date the same as BC/AD system– Examples
220 BC = 220B CEAD 499 = 499 CE
• Question: Why have a new system?
BP Before Present System
• You may also see, especially in scientific contexts the BP dating system
• This is often used for very big periods of time• To calculate the BCE/BC date take the BP date
and minus this year (or the year of publication)– Example: 40 000 BP = 40 000 – 2015 = 37 987 BCE
Bigger Units of Time
• What is a millennium?• What is a decade?• What is a century?
• How are centuries named?• Activity
How do we date artefacts?
• Relative dating– Examples– Only gives sequence in relation to other objects
from the site• Absolute dating– Gives a date for an object (within a probable
range)
Absolute Dating Methods
• Scientific ways to arrive at precise dates include:– Radio-carbon dating– Dendrochronology– Potassium-Argon dating– Thermoluminescence dating– Amino-acid dating
Radio-carbon C-14 datingVideo: 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 Dendochronology
• 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
Activities
• Complete the dendrochronology activity• Complete the dating systems activity• Go onto CGS Connect and look at the Prep for
this week