The Age of Things:Sticks, Stones and the Universe

Correcting and Using Carbon 14

http://cfcp.uchicago.edu/~mmhedman/compton1.html

Last Time:

Current Carbon-14 FractionOriginal Carbon-14 FractionR =

Carbon-14 Fraction = Carbon 14All Carbon

R

A personal aside:

R

This says the tree from which thissample was taken was fallen ~14000 yrsago. However, (we) cannot judge this date asvalid w/o adequate context: Does this datemake sense in terms of other dates at

the site? For a single date is not very reliable in these situations. Furthermore, is the sample contaminated? Could there be factors that would cause the date to be erroneous? Also the date has not been properly altered to take into account fluctuations in radiocarbon levels from year to year. Finally, even if the above factors were taken into account, we only know when the tree was cut down (when it stopped taking up CO2) we have no idea how long it might have sat around before being used in a fire. Therefore, unfortunately, we cannot tell when the fire occurred with the limited data given.

My Answer:

Current Carbon-14 FractionOriginal Carbon-14 FractionR =

Measured with radioactivity or AMS methods

Measured using a contemporary reference sample

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Warning!

AstrophysicistTalking aboutTree-Rings!

Correcting Carbon-14With Tree Rings

Dendrochronology

Calibrating Carbon-14 Dates with Tree Rings

Calibrating Carbon-14 Dates with Tree Rings

Estimated Age

Estimated Ratio

Current Carbon-14 FractionOriginal Carbon-14 FractionR =

R

Estimated Age

Actual Age

Actual Ratio

Estimated Ratio

Current Carbon-14 FractionOriginal Carbon-14 FractionR =

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Atmospheric Carbon-14 fraction changes with time

The Changing Magnetic field

Calibrating Carbon-14 Dates with Tree Rings

Calibrating Carbon-14 Dates with Tree Rings

Calibrating Carbon-14 Dates with Tree Rings

Calibrated Carbon-14 Dates

Complications

Complications

The Early Americans

Warning!

Astrophysicist Talking About Archaeology

Clovis Points

The Land Bridge

Clovis Mammoth kills

Glaciers around 12,000 BP

Clovis and the Ice-Free Corridor

The “Clovis-First” Model

Are thereSites earlier thanClovis?

Meadowcroft

The MeadowCroft Rockshelter

Dates at Meadowcroft

Dates at Meadowcroft

1265 AD

980 BC -1305 BC

1260 BC - 6060 BC

1025 AD - 660 AD

1775 AD

340 BC - 870 BC285 AD - 125 BC

10,850 BC - 14,255 BC +

Monte Verde

A Coastal Route?

What is really Important about Monte Verde

Monte Alegre

Temporal Relationships within a site

Temporal relationships between sites

Mammoth Hunters

Forest Foragers

How did people live in the New World?

Rather than:How did people get into the New World?

Next Time

Potassium, Argon,

Genes and

Walking Upright