Physics Fills the Gap for Java Man

Garrison replies: I hope I did not say there is a “gap” in our ability to date the late to mid-Pleistocene. I hoped to imply that there was a real gap, in the recent past, that I estimated to be about 500 ka—a singularly awkward time interval, since it is when the real evolution of anatomically modern humans (AMH) occurred. The present-day suite of dating techniques—uranium disequilibrium series; thermoluminescence (TL) and optical-stimulated luminescence; electron-spin resonance; and fission track—together with radiocarbon and argon/argon, now offer archaeologists a range of methods mostly unavailable or “unrecognized” before the last quarter of the 20th century.

I disagree with Karner on the revolutionary role of accelerator mass spectrometry-radiocarbon. AMS is sensitive to parts per quadrillion levels, but that still will not get us dates beyond the 50-ka limit, even with smaller samples. It is certainly a boon in limiting the destruction of rare and important archaeological specimens. AMS did give us the 24-ka age of the Neanderthal child found on the Iberian Peninsula, which raised issues of genetic mixing of AMH and Neanderthal. ¹ New AMS dates for AMH and Neanderthal remains found at the Balkan sites of Hrvatsko Zajorje, Velika Pecina, and Vindija G1 ² raise the same issues in Europe proper for the same period.

As to uncertainties in TL ages, a recent study ³ has produced a remarkable correspondence between TL dates and tree-ring results—40% (6 of 15) from the same-site context. Likewise, three of the remaining samples were seen to be correspondent by use of bridging arguments for the dendrochronological data. Not bad.

As to Carl Swisher’s professional attribution, I can only repeat what I read in the journals. Proper credit is due any benefactors responsible for dating, or redating, Java Man. No slight was intended.