The Daily Telegraph reported that strands of hair from a human who lived 200,000 years ago have been found preserved inside fossilised hyena dung from South Africa. This is noteworthy because up until now the oldest samples of human hair were from a 9,000 year old mummy found in northern Chile.
How have these hairs been dated? In the original article in the Journal of Archaeological Science (Volume 36, 2009, pp.1269-1276) on which the story is based it explains:
The internal deposits are unusual for caves in the region in that they are stratified, clearly exposed and well preserved. Interbedded within the strata are flowstones that act as chronostratigraphic markers and are used to divide the sediments into flowstone-bounded units (FBUs) that may be absolutely dated by the Uranium–Thorium (U–Th) method (Pickering et al., 2007). The fossil hyaena latrine is situated in FBU 14, which has well-developed lower flowstones and a small stalagmite at the base of the unit. Samples for Uranium-series dating were taken from the lower and upper flowstones binding unit 14, as well as from the top of the small stalagmite. The preparation and measurement of samples for U–Th dating, as well as age calculations, are fully described in Pickering et al. (2007). The flowstone at the base of the coprolite unit has a U–Th age of 255,297 (+-2510 years). The flowstone layer above was poorly preserved, contained very little Uranium and some detrital Thorium. The best age estimates are 225,818 (+-30,462) and 240,805 (+-15,966) years, thus constraining the age of the coprolites to between ~195,000 and 257,000 years old.
[Pickering et al. (2007) refers to Pickering, R., Hancox, P.J., Lee-Thorp, J., Grun, R., McCulloch, M., Mortimer, G.E., Berger, L.R., 2007. Stratigraphy, U–Th chronology and palaeoenvironments at Gladysvale Cave: insights into the climatic control of South African hominin bearing caves. Journal of Human Evolution 53, 602–619].
I should also add that the hairs haven't been absolutely identified as human. The original article goes on to say:
Considering that the original position of the fossil hairs on the animal is unknown, that the internal structure is obscured – because the chemistry of the hair has been transformed by the digestive process and diagenetic alteration within the coprolite – and that natural pigmentation is absent, precise identification presents a considerable challenge.
It then concludes :
The depositional environment and lack of organic matter were not conducive to DNA preservation, which may have resolved the taxonomic identity of the mammal hair. However, what remains are remarkably well-preserved casts of the original hair scales, although with some loss of surface form. It is suggested that there is still sufficient information to make a tentative identification of the species represented. Small mammals, carnivores and bovids, which commonly occur in hyaena scats today, are unlikely candidates based on the scale pattern observed. It is suggested that the family primates is most likely represented by the fossil coprolite hair, and of this group, human hair is most probably indicated.