Application of Optical Dating to Fossil and Tool-Bearing Cave Sediments at Atapuerca, Spain

在美国国家科学基金会的支持下，格伦·伯格博士将在位于西班牙布鲁戈斯以东14公里的阿塔普埃尔卡地区进行两个季节的实地研究。一条废弃的铁路沟渠穿过一系列藏有极其重要的原始人类材料的洞穴，这项研究的目标是准确地确定它们的年代。虽然人类学家知道原始人早在180万年前就在非洲进化并离开了这片大陆，但直到最近，欧洲最早可靠的年代材料的年代还不到50万年。看来，原始人类在进化史上进入这一地区的时间相对较晚。在这种背景下，最近在阿塔普尔卡地区挖掘的一系列遗址尤为重要，因为它们包含了大量的原始人类骨骼材料，以及石器和相关的动物遗骸。根据古地磁证据，很明显，这些事件中最古老的年龄超过了78万年。伯杰博士将使用IR-OSL分析两个地点的沉积物，以确定其中两个地点沉积物水平的相对年龄，并希望确定绝对年龄。超过4万年的更新世时代沉积物——放射性碳的有效范围——与火山物质无关，很难确定其年代。目前采用的实验技术往往不能产生一致的信息。伯杰博士正致力于开发一种光激发热发光技术，这种技术可以应用于长石而不是更常见的石英晶体。热释光定年法测量晶体中累积的随时间辐射引起的损伤。人们相信，阳光会把石板擦得干干净净，把时钟调到零。因此，在测定沉积物的年代时，人们实际上确定的不是颗粒本身的年龄，而是它们最后一次暴露在阳光下的时间。在考古情况下，与骨头和文化材料有关的沉积物被埋在连续的泥土层下，最后一次暴露在阳光下是有用的信息。但问题是，阳光可能并不总是把时钟调到零，伯杰博士除了从阿塔普尔卡遗址收集埋藏的材料外，还将启动一个更广泛的地质调查项目。他将收集与掩埋地点相同的暴露沉积物，并将其作为对照。这项研究不仅将为重要的原始人类和相关文化遗迹提供年龄估计。它还将进一步发展热释光测年技术，该技术在许多人类学、地质学和古生物学领域具有潜在的应用前景。

With National Science Foundation support Dr. Glen Burger will conduct two seasons of field research in the Atapuerca region, located 14 km East of Brugos, Spain. An abandoned railway trench cuts through a series of caves which hold extremely important hominid materials and the goal of this research is to date them accurately. Although anthropologists know that hominids evolved in Africa and left this continent as early as 1.8 million years ago, until recently the earliest securely dated materials in Europe dated to less than a half million years in age. It appeared that hominids entered this region only relatively late in their evolutionary history. In this context, a series of recently excavated sites in the Atapuerca region are particularly important because they contain an abundance of hominid skeletal material as well as stone tools and associated faunal remains. Based on paleomagnetic evidence it is clear that the oldest of these occurrences exceed 780,000 years in age. Dr. Berger will analyze the sediments from two sites using IR-OSL to determine the relative - and hopefully the absolute - ages of levels from two of these sites. Pleistocene age sediments older than 40,000 years - the effective range of radiocarbon - and not associated with volcanic materials are extremely difficult to date. The experimental techniques currently employed often do not yield consistent information. Dr. Berger is working to develop an optically stimulated thermolumenescent technique which can be applied to feldspar rather than more commonly studied quartz crystals. Thermolumenescence dating measures time dependent radiation induced damage which accumulates in crystals. Sunlight, it is believed, wipes the slate clean and sets the clock to zero. Thus in dating sediment, one in fact determines not the age of the particles themselves but rather the last time they were exposed to the sun. In archaeological situations where sediments associated with bones and cultural material are buried under successive layers of dirt, last exposure to the sun is useful information. The problem however is that sunlight may not always set the clock to zero and Dr. Berger, in addition to collecting buried materials from the Atapuerca sites, will initiate a broader program of geological survey. He will collect exposed sediments identical to those buried in the sites and use these as controls. This research will not only provide age estimates for important hominid and associated cultural remains. It will also further development of the thermolumenescent dating technique which is potentially applicable in many anthropological, geological and paleontological contexts.