“北京人”化石年龄重新确定

　　

生物通报道：昨天刚刚出版的Nature（3月12日）的封面图片就是一颗北京人头颅化石，这一期的Nature在多个方面关注了中国，分别为化石研究，汶川地震，环保问题和禽流感问题。

第一篇是封面文章，来自南京师范大学，中国科学院古脊椎动物与古人类研究所的研究人员重新确定“北京人”化石年龄，他们的计算结果表明，它们的年龄约77万年，比人们通常所想的早近30万年。

以“北京人”为人们所熟知的“直立人”（Homo erectus）头盖骨在古人类学及公众想象中都占据一个重要位置，这不仅是因为它是最早发现的“人族”（hominin）化石之一，而且是因为它的发现地。“北京人”化石是上个世纪30年代在周口店村附近龙骨山遗址发现的。自那时起，关于这些化石的年龄一直存在激烈争论，但这个问题现在利用最近开发的一项技术已经解决，该技术通过测量所埋藏的、来自宇宙的铝-26和铍-10元素来确定洞穴沉积物的年代。计算结果表明，它们的年龄约77万年，比人们通常所想的早近30万年。这一结果表明，原始人类在一些相当寒冷的时期就在那里生活；该结果还对认为早期原始人类只在温暖的间冰期向北迁移的某些已被人们接受的观点提出了疑问。

第二篇文章关注的是汶川地震，美国哈佛大学的研究人员证明汶川地震由地壳收缩造成。作为喜马拉雅山东缘的龙门山山系，比青藏高原上任何地方的地形起伏都大。它是2008年汶川7.9级大地震的发生地。在这次地震之前，无论是测地学还是地质学测量工作都没有测出该山系前端有明显收缩现象，从而引发了关于产生该山系之地形的作用力的激烈争论。现在，Judith Hubbard 和 John Shaw发表了来自平衡的地质横断面的证据，该证据表明，地壳收缩是龙门山和青藏高原隆起的一个主要作用力，2008年汶川地震是这一收缩过程的一个结果。

其次，题为“Delicate balance”的社论和新闻“Putting China's wetlands on the map”则分别聚焦了中国的环保问题和禽流感问题。

（生物通：万纹）

原文摘要：

Age of Zhoukoudian Homo erectus determined with 26Al/10Be burial dating

The age of Zhoukoudian Homo erectus, commonly known as 'Peking Man', has long been pursued, but has remained problematic owing to the lack of suitable dating methods1, 2, 3, 4, 5, 6, 7. Here we report cosmogenic 26Al/10Be burial dating of quartz sediments and artefacts from the lower strata of Locality 1 in the southwestern suburb of Beijing, China, where early representatives of Zhoukoudian Homo erectus were discovered. This study marks the first radioisotopic dating of any early hominin site in China beyond the range of mass spectrometric U-series dating. The weighted mean of six meaningful age measurements, 0.77 0.08 million years (Myr, mean s.e.m.), provides the best age estimate for lower cultural layers 7–10. Together with previously reported U-series dating of speleothem calcite3 and palaeomagnetic stratigraphy4, as well as sedimentological considerations8, 9, these layers may be further correlated to S6–S7 in Chinese loess stratigraphy or marine isotope stages (MIS) 17–19, in the range of 0.68 to 0.78 Myr ago. These ages are substantially older than previously supposed and may imply early hominin's presence at the site in northern China through a relatively mild glacial period corresponding to MIS 18.

Uplift of the Longmen Shan and Tibetan plateau, and the 2008 Wenchuan (M = 7.9) earthquake

The Longmen Shan mountain range, site of the devastating 12 May 2008 Wenchuan (M = 7.9) earthquake, defines the eastern margin of the Himalayan orogen and exhibits greater topographic relief than anywhere else in the Tibetan plateau. However, before the earthquake, geodetic and geologic surveys measured little shortening across the range front1, 2, 3, inspiring a vigorous debate about the process by which the topography of the mountain belt is produced and maintained. Two endmember models have been proposed: (1) brittle crustal thickening, in which thrust faults with large amounts of slip that are rooted in the lithosphere cause uplift4, and (2) crustal flow, in which low-viscosity material in the lower crust extrudes outward from the Tibetan plateau and inflates the crust north and east of the Himalayas5, 6, 7. Here we use balanced geologic cross-sections to show that crustal shortening, structural relief, and topography are strongly correlated in the range front. This suggests that crustal shortening is a primary driver for uplift and topography of the Longmen Shan on the flanks of the plateau. The 2008 Wenchuan (M = 7.9) earthquake, which ruptured a large thrust fault along the range front causing tens of thousands of fatalities and widespread damage, is an active manifestation of this shortening process.