Changes

===Radiocarbon dates for Thera===

===Radiocarbon dates for Thera===

After digging through the vast mantle of tephra, archaeologists found the remains of the Theran town Aktorini. There were no bodies in the remains of the village, indicating there were warning signs that were heeded by the residents before the full eruption. They left behind some storage jars with seeds. Short-lived vegetation such as seeds, when available, are always preferable for radiocarbon dating to larger vegetation specimens such as building lumber, because the dating of lumber reflects the time the tree was growing, which may have been decades before it was cut down and another unspecified length of time while it was in use in the building. These seed specimens were analyzed in a 2004 ''Radiocarbon'' article.<ref>"Dating the Volcanic Eruption at Thera," by Christopher Ramsey, Sturt Manning, and Marigrazia Galimberti, ''Radiocarbon'' 46 (2004), pp. 325-344), available [http://digitalcommons.library.arizona.edu/holdings/journal/issue?r=http://radiocarbon.library.arizona.edu/Volume46/Number1/ here]</ref> The results of this analysis placed the eruption of Thera between 1663 and 1599 BC at a 95% confidence level. Other results obtained from an olive branch with leaves still on it were in agreement: 1660 to 1600 BC.<ref>''Science'' 312, April 28 2006, p. 508.</ref>

After digging through the vast mantle of tephra, archaeologists found the remains of the Theran town Aktorini. There were no bodies in the remains of the village, indicating there were warning signs that were heeded by the residents before the full eruption. They left behind some storage jars with seeds. Short-lived vegetation such as seeds, when available, are always preferable for radiocarbon dating to larger vegetation specimens such as building lumber, because the dating of lumber reflects the time the tree was growing, which may have been decades before it was cut down and another unspecified length of time while it was in use in the building. These seed specimens were analyzed in a 2004 ''Radiocarbon'' article.<ref>"Dating the Volcanic Eruption at Thera," by Christopher Ramsey, Sturt Manning, and Marigrazia Galimberti, ''Radiocarbon'' 46 (2004), pp. 325-344), available [http://digitalcommons.library.arizona.edu/holdings/journal/issue?r=http://radiocarbon.library.arizona.edu/Volume46/Number1/ here]</ref> The results of this analysis placed the eruption of Thera between 1663 and 1599 BC at a 95% confidence level. Other results obtained from an olive branch with leaves still on it were in agreement: 1627 to 1600 BC with a 95% confidence level.<ref>''Science'' 312, April 28 2006, p. 508.</ref>

===Pottery dating of the Thera event===

===Pottery dating of the Thera event===

==Possible explanations of the conflict==

==Possible explanations of the conflict==

It has been proposed by various observers that the Thera event itself may be responsible for the discrepancy between radiocarbon dates and archaeological dates in the middle of the second millennium BC. It is already recognized that a change in the earth's magnetic field will affect the number of cosmic rays reaching the upper atmosphere, and hence the number of C¹⁴ isotopes being formed, and this explanation is used as part of the explanation of why the C¹²/C¹⁴ ratio does not follow a straight line over the centuries, as compared to figures derived from dendrochronology. But a cataclysmic event can also distort the ratio of these two isotopes. Nuclear and thermonuclear tests in the late 1950s and early 1960s that were carried out mostly (entirely, for the thermonuclear events) in the South Pacific affected the C¹²/C¹⁴ ratio for several years afterward in both hemispheres. If the Thera event gorged up old carbon material from inside the earth, then the distribution of the old carbon in the atmosphere would make any plant material than took it up to appear older than it actually was when measured in mass spectrometers some 3500 years later. There is no consensus yet on such an explanation, however, and it may be that some other effect, yet unaccounted for, explains the radiocarbon results without requiring any adjustment to the archaeological data.  

It has been proposed by various observers that the Thera event itself may be responsible for the discrepancy between radiocarbon dates and archaeological dates in the middle of the second millennium BC. It is already recognized that a change in the earth's magnetic field will affect the number of cosmic rays reaching the upper atmosphere, and hence the number of C¹⁴ isotopes being formed, and this explanation is used as part of the explanation of why the C¹²/C¹⁴ ratio does not follow a straight line over the centuries, as compared to figures derived from [[dendrochronology]]. But a cataclysmic event can also distort the ratio of these two isotopes. Nuclear and thermonuclear tests in the late 1950s and early 1960s that were carried out mostly (entirely, for the thermonuclear events) in the South Pacific affected the C¹²/C¹⁴ ratio in both southern and northern hemispheres. If the Thera event gorged up old carbon material from inside the earth, then the distribution of the old carbon in the atmosphere would make any plant material than took it up to appear older than it actually was when measured in mass spectrometers some 3500 years later.  

 

This explanation, however, does not seem possible because of the olive branch that was buried in Thera's eruption. Growth rings in the branch represented 70 years of growth for the tree. Samples from various rings were subjected to radiocarbon analysis. The result was that the earliest rings returned values that measured about 70 years earlier than the latest rings and the leaves. This implies that if something had disturbed the atmospheric C¹²/C¹⁴ ratio for the mid-second millennium BC, the disturbance was in effect at least 70 years before the Thera eruption.

 

Another explanation for the apparently too-early C¹⁴ readings is that the calibration curves are distorted because these curves are based largely on reconstructions of the [[dendrochronology]] for this time, and it is conjectured that the dendrochronological data are in error. Dendrochronological adjustments continue to be a matter of controversy, partly because of the failure to publish a thorough sequence of tree-ring data back as far as the second millennium BC.

==Practical considerations==

==Practical considerations==