Radiocarbon dating has the following limitations

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The influence of humans is of world extent and is so profound that it seems appropriate to have a special geologic name for this time. The Holocene represents the most recent interglacial interval of the Quaternary period.

This has been particularly useful where arrowheads of obsidian are included in deposits.The magnetized material to be studied can be natural, such as a lava flow; or it may be man-made, as, for example, an ancient brick kiln or smeltery that has cooled and thus fixed the magnetic orientation of the bricks to correspond to the geomagnetic field of that time. The wind may blow the ash 1,500–3,000 kilometres, and, because the minerals or volcanic glass from any one eruptive cycle tend to be distinctive from those of any other cycle, even from the same volcano, these can be dated from the associated lavas by stratigraphic methods (with or without absolute dating).The ash layer then can be traced as a “time horizon” wherever it has been preserved.Here, we use mitochondrial genome sequences from ten securely dated ancient modern humans spanning 40,000 years as calibration points for the mitochondrial clock, thus yielding a direct estimate of the mitochondrial substitution rate.Our clock yields mitochondrial divergence times that are in agreement with earlier estimates based on calibration points derived from either fossils or archaeological material.

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