The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia

Abstract

Homo erectus was the first human lineage to disperse widely throughout the Old World, the only hominin in Asia through much of the Pleistocene, and was likely ancestral to H. sapiens. The demise of this taxon remains obscure because of uncertainties regarding the geological age of its youngest populations. In 1996, some of us co-published electron spin resonance (ESR) and uranium series (U-series) results indicating an age as young as 35–50 ka for the late H. erectus sites of Ngandong and Sambungmacan and the faunal site of Jigar (Indonesia). If correct, these ages favor an African origin for recent humans who would overlap with H. erectus in time and space. Here, we report 40Ar/39Ar incremental heating analyses and new ESR/U-series age estimates from the “20 m terrace" at Ngandong and Jigar. Both data sets are internally consistent and provide no evidence for reworking, yet they are inconsistent with one another. The 40Ar/39Ar analyses give an average age of 546±12 ka (sd±5 se) for both sites, the first reliable radiometric indications of a middle Pleistocene component for the terrace. Given the technical accuracy and consistency of the analyses, the argon ages represent either the actual age or the maximum age for the terrace and are significantly older than previous estimates. Most of the ESR/U-series results are older as well, but the oldest that meets all modeling criteria is 143 ka+20/−17. Most samples indicated leaching of uranium and likely represent either the actual or the minimum age of the terrace. Given known sources of error, the U-series results could be consistent with a middle Pleistocene age. However, the ESR and 40Ar/39Ar ages preclude one another. Regardless, the age of the sites and hominins is at least bracketed between these estimates and is older than currently accepted.

Global and local perspectives on cranial shape variation in Indonesian <i>Homo erectus</i>

“…It is unclear whether or how the Sm 1 and Sm 2 fossils are related, but this could lend support to an older age for the Sambungmacan hominins. However, both Swisher et al (1996) and Yokoyama et al (2008) support very late Pleistocene ages for Sambungmacan as discussed above (but see Indriati et al (2011)). Thus, the range of dates for Sambungmacan encompasses the Early to Late Pleistocene and may predate, post-date, or be synchronous with Ngandong.…”

“…The former suggested a Middle Pleistocene age of 546 ka, while the latter suggested younger ages between 77 and 143 ka for combined ESR and U-series dating, and as young as 44 ka based on the closed system ESR alone. Indriati et al (2011) conclude that a reasonable age range for Ngandong is 546-143 ka, but do not rule out that the fossils may be closer to the older end of the range, with the younger dates reflecting a more recent geomorphologic or hydrologic event. However, Yokoyama et al's (2008) gamma-ray spectrometric dating of three hominin fossils from Ngandong and Sambungmacan yielded young ages between 40 and 70 ka, which is more consistent with the ESR dates.…”

“…Yokoyama et al (2008) found similar dates for two Ngandong (Ng 1 and Ng 7) and one Sambungmacan (Sm 1) fossil, suggesting that this assumption may be correct for at least some of the specimens. Yet, the very young date reported by Yokoyama et al (2008) may reflect more recent hydrological activity unrelated to the actual deposition of these fossils (Indriati et al, 2011). Deposits spanning the Pleistocene are found in the area of the Sm 1 findspot (Kaifu et al, 2008).…”

“…Itihara et al (1985) suggested a Late Pleistocene age for these same deposits, and Swisher et al (1996) posited a very young age of 53-27 ka for both Ngandong and Sambungmacan. More recent geological work at Ngandong by Indriati et al (2011) found two internally consistent but mutually exclusive sets of dates based on 40 Ar/ 39 Ar dating of hornblende from within the fossiliferous layers versus ESR and U-series dating of fossil teeth. The former suggested a Middle Pleistocene age of 546 ka, while the latter suggested younger ages between 77 and 143 ka for combined ESR and U-series dating, and as young as 44 ka based on the closed system ESR alone.…”

<i>Homo erectus</i> calvaria from Ngawi (Java) and its evolutionary implications

“…The Ngandong series is from the Ngandong High Terrace, and is generally dated to the early Late Pleistocene (Yokoyama et al, 2008;Huffman et al, 2010), although controversy still continues about their exact dates (Indriati et al, 2011). This assemblage can be called 'late' Javanese H. erectus.…”