HOW OLD IS IT?
How Science helps the Archaeologist
Modern archaeologists have a variety of scientific dating methods they can
use to determine an object’s age. What follows is a guide to these methods:
Cross-Dating:
In cross-dating, archaeologists compare artefacts from a dated site with
artifacts from an undated site. If the artefacts are similar in style, there
is a good possibility they were made at around the same time.
Dendro-Chronology:
This method uses tree rings to date objects made of wood. Trees show a
growth ring for every year of their life. The width of the ring depends upon
the climate of that year. No two years are identical. By using samples of
wood which grew over many years in one location, archaeologists can create a
master chart of tree-ring growth. Matching a wooden object with the
master chart can reveal the exact year the tree was cut.
Radiocarbon or Carbon 14:
All living organisms contain radioactive carbon 14. After the organism dies,
the carbon 14 atoms break down at a known and constant rate. By measuring
the amount of carbon 14 remaining in an object, an archaeologist can
determine the age of the object. Carbon 14 dating can be used accurately on
objects no older than 50,000 years.
Potassium-Argon:
To date volcanic rock, a process similar to radiocarbon dating is used. By
measuring the amount of argon gas remaining as the potassium in the rock
decays to radioactive argon at a fixed rate, an archaeologist can determine
the age of the rock. Since potassium decays very slowly, potassium-argon
dating can be used for objects over one million years old.
Exercise:
Below is a list of objects you might find in an excavation. Which dating techniques
would you use?
Object
Dating Techniques
1. Bronze axe blade
______________________________
2. Piece of charcoal
______________________________
3. Skull Fragment
______________________________
4. Roof Beam
______________________________
5. Decorated pottery bowl
______________________________
6. Fossil in lava rock
______________________________
7. Wooden sarcophagus
______________________________
8. Layer of volcanic deposits
______________________________
9. Dried grain
______________________________
10. Leather sandal fragment
______________________________