Although the geochronology of the site is complex, these lines of evidence show that the minimum age of the Chusang site, as dated by a
consistent set of 230Th/U ages taken from a single
generation of clean pore cement postdating the
prints, is 7. 4 ± 0.1 thousand years. Although we
cannot state with certainty a maximum age for
the site, we can offer two alternatives: (i) a maximum age of the prints of 8. 20 to 8. 51 thousand
years cal. B.P., constrained by 14C assays (ABA
ages) of the colluvium immediately below the
travertine sheet, or (ii) a maximum age of the
prints of 12. 7 thousand years cal. B.P. (ABOxA
age from the same colluvium), which is consistent with the OSL dates on travertine that range
from 10.0 to 14.0 thousand years ago. For either
scenario, these ages make Chusang the oldest
reliably dated archaeological site on the high-elevation step of the Tibetan Plateau.
This finding has important implications for
evaluating current models of the peopling of
the Tibetan Plateau. For Chusang to be a station
( 23) or task-specific site monitored seasonally from
a base camp at a lower elevation (<3300 masl),
travel costs would have been considerable.
Travel cost modeling shows that round-trip
travel times from such a base camp would have
minimally required 28 to 47 days ( 19) (fig. S11A).
However, this route would have had to cross
the eastern Himalayan range and would have
been impassable for much of the year, especially
during the early Holocene, because of the closure
of high passes by heavy snowfall and expansion
of valley glaciers in response to increased pre-
cipitation from the Indian summer monsoon
( 9, 24). A more plausible route (fig. S11B) from
the southeast shows a round-trip travel time of
41 to 70 days. Such travel is unlikely to have been
undertaken for seasonal, short-term task pursuits
in rugged, mountainous terrain, particularly
by age-variable groups that may have included
children, as is suggested by the presence of small
footprints at Chusang ( 17, 25). These estimates
also exceed annual travel distances for most
ethnographically known foraging peoples ( 26, 27).
Instead, the data from Chusang support a model
of an annual settlement pattern focused on the
high interior plateau that likely used adjacent
valleys of the major river courses at elevations
above 3600 masl. Although we cannot entirely
rule out the possibility of the logistical use of
Chusang by low-elevation foragers, our analy-
ses of archaeological, geographic, demographic,
environmental, and ethnographic evidence con-
verge to suggest that this type of use was highly
The data from Chusang support the presence of an early, pre-agropastoral population
on the high-elevation step of the Tibetan Plateau
~ 7. 4 to 8. 4 thousand years ago, although an
earlier presence 12 to 13 thousand years ago
cannot be fully discounted. These dates are consistent with what is known of the ancestral genetics of modern Tibetans ( 11–15) and coincide
with wet and humid climate conditions on the
Tibetan Plateau that lasted from 11. 5 until
4.2 thousand years ago because of an enhanced
Indian summer monsoon ( 28–30). Although an
agropastoral lifeway may have enabled substantial population growth after 5 thousand years B.P.,
it by no means was required for the early, likely
permanent, occupation of the high central valleys of the Tibetan Plateau.
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This research was funded by the Austrian Science Fund
(FWF; grant P 249340_G19) and the U.S. National Science
Foundation (grant BCS-0244327). Z. W. was supported by the
Chinese Scholarship Council. G. Mutri drew the lithics. R. Tessadri
performed x-ray diffraction measurements. J. Turnbull and
C. Prior supported the 14C dating campaign. We thank four
anonymous reviewers for constructive comments that improved
the manuscript. Data are available in the supplementary
Materials and Methods
Figs. S1 to S16
Tables S1 to S5
5 May 2016; accepted 25 November 2016
Fig. 3. Well-preserved human footprints at Chusang. The footprints are visualized with (A) a three-dimensional model and (B) a corresponding field image. (C) The annual travertine layers below the imprints are bended, suggestive of human presence during travertine formation. The porous summer layers
contain numerous cement generations that precipitated shortly after travertine deposition. For the laminated pore cement, a 230Th/U age of 7. 4 thousand years was obtained, providing a robust minimum age for