Re: 30,000 year old Homo erectus

Dan Barnes (dbarnes@liv.ac.uk)
Tue, 17 Dec 1996 13:04:37 GMT

The dates are ESR and U-series dates from enamel taken from fauna
associated with the hominid find beds at Ngandong and Sambungmacan. I am
currently doing U-series dating at Liverpool and have recently spoken to Jack
Rink at McMasters who (along with Henry Schwarcz) did the dating work. There
are three major objections I can think of all of (but I would appreciate any
other suggestions) which are either impossible, incredibly unlikely or have been
dealt with. They are:
1. The teeth are from a younger formation that were mixed with the hominids
during a period of erosion and redeposition. However, the weathering and
flourine levels are identical for the teeth and the hominids suggesting a similar
age. Although the finds have been transported fine features are still preserved
and close association of finds from individuals suggest a short distance of
transport.
2. Thorium has been leached out making the date too young. This is
geochemically impossible as the uranium is more mobile and so if the teeth had
been open system then the ages would be higher not lower.
3. The uranium was taken up recently. Although this hasn't been published the
Recent Uptake model (i.e. all the uranium was added last week) gives the
highest possible age and this would only be in the region of 160 ka. Not only is
this extremely unlikely (verging on the impossible) but the date would still not be
of acceptable antiquity.

In fact there is some evidence for uranium leaching out recently making the
dates older than they should be. It should be added that more recent
ESR/U-series dates (where there has been a sufficient amount of uranium
uptake, as occured here) a less susceptible to inaccuracy as older dates
because the processes of leaching would only make dates older not younger.

I would say with our current knowledge these dates seem to be correct i.e. H.
erectus in Java surivived into the time period 53 - 27 ka (of course I could be
wrong and radiocarbon dates, which weren't done because it was thought the
hominids were too old, will help to confirm or refute these dates).

For further info and links see:

http://www.dealsonline.com/origins/news/article17.htm

Dan