How Old Is Stonehenge?
Approximately 8 miles north of Salisbury,Wiltshire, England, stands a large circular
stone monument surrounded by an earthwork.This prehistoric structure is
known throughout the world as Stonehenge. Its name is derived from the Old
English word hengen, referring to something hung up. In the case of the monument,
this name refers to the large horizontal lintel stones.The monument consists
of an outer ring of sarsen stones, surrounding two inner circles of
bluestones.The first and third circles are adorned with the familiar stone lintels.
The entire structure is surrounded by a ditch and bank. Just inside the bank are
56 pits, named the Aubrey Holes, after their discoverer. These holes appear to
have been filled shortly after their excavation.
Recently, it has been discovered that a number of the stone alignments are
associated with important solar and lunar risings and settings, suggesting that
the site served as some sort of massive astronomical calendar. If this conclusion
is accurate, it seems likely that the monument might have been used as a temple
for sky worshipers.
Corinn Dillion is interested in dating the construction of the structure. Excavations
at the site uncovered a number of unshed antlers, antler tines, and animal
bones. Carbon 14 dating methods were used to estimate the ages of the
Stonehenge artifacts. Carbon 14 is one of three carbon isotopes found in Earth’s
atmosphere. Carbon 12 makes up 99% of all the carbon dioxide in the air.Virtually
all the remaining 1% is composed of carbon 13. By far, the rarest form of
carbon isotope found in the atmosphere is carbon 14.
The ratio of carbon 14 to carbon 12 remains constant in living organisms.
However, once the organism dies, the amount of carbon-14 in the remains of
the organism begins to decline, because it is radioactive, with a half-life of
5730 years (the “Cambridge half-life”). So the decay of carbon-14 into ordinary
nitrogen makes possible a reliable estimate about the time of death of
the organism. The counted carbon 14 decay events can be modeled by the
Dillion’s team used two different carbon 14 dating methods to arrive at age
estimates for the numerous Stonehenge artifacts.The liquid scintillation counting
(LSC) method utilizes benzene, acetylene, ethanol, methanol, or a similar
chemical. Unlike the LSC method, the accelerator mass spectrometry (AMS)
technique offers direct carbon 14 isotope counting.The AMS method’s greatest
advantage is that it requires only milligram-sized samples for testing.The AMS
method was used only on recovered artifacts that were of extremely small size.
Stonehenge’s main ditch was dug in a series of segments. Excavations at the
base of the ditch uncovered a number of antlers, which bore signs of heavy use.
These antlers could have been used by the builders as picks or rakes. The fact
that no primary silt was discovered beneath the antlers suggests that they were
buried in the ditch shortly after its completion. Another researcher, Phillip
Corbin, using an archeological markings approach, had previously claimed that
the mean date for the construction of the ditch was 2950 B.C. A sample of nine
age estimates from unshed antlers excavated from the ditch produced a mean of
3033.1 B.C., with standard deviation 66.9 years. Assume that the ages are normally
distributed with no obvious outliers. At an significance level, is
there any reason to dispute Corbin’s claim?
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