What was built at stonehenge in 2950 bc

Y CASE STUDY

How Old Is Stonehenge?

Approximately 8 miles north of Salisbury, Wiltshire, England, stands a large cir- cular 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 monu- ment, this name refers to the large horizontal lintel stones. The monument con- sists 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. Ex- cavations at the site uncovered a number of unshed antlers, antler tines, and an- imal 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. Vir- tually 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 ordi- nary 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 normal distribution.

Dillion’s team used two different carbon 14 dating methods to arrive at age estimates for the numerous Stonehenge artifacts. The liquid scintillation count- ing (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 nor- mally distributed with no obvious outliers. At an significance level, is there any reason to dispute Corbin’s claim?

a = 0.05

Four animal bone samples were discovered in the ditch terminals. These bones bore signs of attempts at artificial preservation and might have been in use for a substantial period of time before being placed at Stonehenge. When dated, these bones had a mean age of 3187.5 B.C. and standard deviation of 67.4 years. Assume that the ages are normally distributed with no obvious outliers. Use an significance level to test the claim that the population mean age of the site is different from 2950 B.C.

In the center of the monument are two concentric circles of igneous rock pillars, called bluestones.The construction of these circles was never completed. These circles are known as the Bluestone Circle and the Bluestone Horseshoe. The stones in these two formations were transported to the site from the Pres- celly Mountains in Pembrokeshire, southwest Wales. Excavation at the center of the monument revealed an antler, an antler tine, and an animal bone. Each arti- fact was submitted for dating. It was determined that this sample of three arti- facts had a mean age of 2193.3 B.C, with a standard deviation of 104.1 years. Assume that the ages are normally distributed with no obvious outliers. Use an

significance level to test the claim that the population mean age of the Bluestone formations is different from Corbin’s declared mean age of the ditch, that is, 2950 B.C.

Finally, three additional antler samples were uncovered at the Y and Z holes.These holes are part of a formation of concentric circles, 11 meters and 3.7 meters, respectively, outside of the Sarsen Circle. The sample mean age of these antlers is 1671.7 B.C. with a standard deviation of 99.7 years. Assume that the ages are normally distributed with no obvious outliers. Use an signifi- cance level to test whether the population mean age of the Y and Z holes is dif- ferent from Corbin’s stated mean age of the ditch, that is, 2950 B.C.

From your analysis, does it appear that the mean ages of the artifacts from the ditch, the ditch terminals, the Bluestones, and the Y and Z holes dated by Dillion are consistent with Corbin’s claimed mean age of 2950 B.C. for construc- tion of the ditch? Can you use the results from your hypothesis tests to infer the likely construction order of the various Stonehenge structures? Explain.

Using Dillion’s data, construct a 95% confidence interval for the popula- tion mean ages of the various sites. Do these confidence intervals support Corbin’s claim? Can you use these confidence intervals to infer the likely con- struction order of the various Stonehenge structures? Explain.

Which statistical technique, hypothesis testing or confidence intervals, is more useful in assessing the age and likely construction order of the Stone- henge structures? Explain.

Discuss the limitations and assumptions of your analysis. Is there any addi- tional information that you would like to have before publishing your findings? Would another statistical procedure be more useful in analyzing these data? If so, which one? Explain.Write a report to Corinn Dillion detailing your analysis.

Source: This fictional account is based on information obtained from Archaeometry and Stonehenge (www.eng_h.gov.uk/stoneh). The means and standard deviations used throughout this case study were constructed by calculating the statistics from the midpoint of the calibrated date range sup- plied for each artifact.

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Chapter 10 Case Study

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