Topic 7 – contextual inference: time
- Chronometric (absolute)
o Age in calendar terms (still not absolutely exact though)
o Statistical approximation
- Chronometric dating
o Radiometric
Based on radioactive decay
o Trapped energy
Energy absorbed by ceramic or rock absorbed
Know rate of absorption and loss
o Non-radiometric dating
- Concern of chronology to determine how old something is using chronologic techniques
- Radiocarbon is most trusted for dating things back to 75 000 years
- Radiometric
o Decay of radioactive materials (uranium)
Radiocarbon
Nuclear explosions in the 20th century which blew away the radio
carbon so can’t date recent things of 200 years ago
Potassium/argon
- Radiocarbon 14C
o Organic material only
o 75 000 – 200 ya (years ago)
o For anything older 10 000 years ago, use ya or BP
o Element in the upper atmosphere turn into carbon 14 (isotope of carbon 12) which will
combine with carbon dioxide, carbon dioxide is absorbed by plants which also absorbed
carbon 14, which maintain as long as you are eating, drinking, and whatever until you
die and then the carbon 14 will start to decay
o Carbon 14 amount can be measured, and calibration
Trees form rings, outside older rings are dead
o Grand banks Stratigraphy
TO-5307
1570 +/- 90 bp
Cal.AD 322 – 648
- Potassium/Argon or K/A
o Volcanic rock
o 2 billion – 100, 000 ya
o Potassium doesn’t decay as first as radio carbon
o Olduvai Gorge
Through potassium/argon by Louis and Mary Leakey
KBS tuff
- Richard Leakey