Dating El Gigante

约会埃尔巨人

• 批准号: 1003431
• 负责人: David Webster
• 金额: $ 2.67万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-15 至 2013-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1003431&HistoricalAwards=false
• 关键词: Dating; El; Gigante

National Science Foundation funds will generate an accurate radiocarbon chronology for El Gigante Cave, located in central Honduras. Stratified deposits there have produced extremely well-preserved samples of plant remains, along with animal bone, pottery, and other cultural material. Particularly abundant are macrofossils of maize, a staple crop which today contributes, directly or indirectly, about 21% of the calories ingested by humans worldwide. Despite its significance, the ancient selection processes that led to the emergence of maize is poorly understood. DNA testing shows that maize evolved from annual teosinte, a grass native to sub-tropical regions of Mexico, Guatemala, and Honduras. Still controversial is the chronology of maize evolution, mainly because only a handful of sites have abundant macrofossils - mainly dry caves in the Tehuacan and Oaxaca valleys of Mexico. Maize from Tehuacan was long ago dated to 5000 BC, and the Tehuacan cave chronology provided the general framework for the evolution of maize for almost three decades. This reconstruction abruptly fell apart in 1989 with the application of a new form of radiocarbon dating. Standard radiocarbon methods required large samples of organic material. Tehuacan maize samples were too precious to destroy in the 1960s, so they were indirectly dated - i.e., by using carbon in assumed association from the same strata. Accelerator mass spectrometer (AMS) dating requires only minute samples of organic matter. Macrofossils of maize and other plants can thus be directly dated, eliminating the association assumption. Restudy of the old Tehuacan samples showed that maize was much more recent there than previously thought, and that stratigraphic associations could not be trusted. El Gigante's maize sample is comparable to that from Tehuacan, and includes fragments of other plants utilized by humans. It was mainly used between 2000 - 7000 years ago. The cave thus augments the meager roster of sites useful for investigating the origins of Mesoamerican plant domestication. During the next year some 30 samples of maize and other plant macrofossils from El Gigante, along with other cultural material such as a leather bag, will be dated by the AMS method. These dates will test the reliability of the stratigraphy, and hence form the framework for future studies of the El Gigante collections. If the stratigraphy can be trusted, a much better picture of human use of maize and other plant foods for a period of 5000 years or more will emerge. If, as at Tehuacan, stratigraphy is confused, we will have an unparalleled population of ancient maze from short interval of time - roughly 2000-2500 BC. One broad impact of the study will be to set a standard for adequate independent testing of the chronological implications of cave deposits. Another will be to focus attention on the southwestern margins of Mesoamerica, a region formerly lacking stratified deposits of early plant material that is essential to understanding the spread of early maize from its restricted homeland, and the larger issue of the spread of New World food production.

国家科学基金会的资金将为位于洪都拉斯中部的El Gigante Cave提供准确的放射性碳年代学。 那里的层状沉积物产生了保存极其完好的植物遗骸样本，沿着动物骨骼，陶器和其他文化材料。 特别丰富的是玉米的宏化石，玉米是一种主要作物，今天直接或间接地贡献了全世界人类摄入的卡路里的21%。 尽管其重要性，导致玉米出现的古老选择过程却知之甚少。 DNA测试表明，玉米是从一年生的大刍草进化而来的，大刍草是一种原产于墨西哥、危地马拉和洪都拉斯亚热带地区的草。 玉米进化的年代学仍然存在争议，主要是因为只有少数几个地点有丰富的宏体化石--主要是墨西哥特瓦坎和瓦哈卡山谷的干燥洞穴。 特瓦坎的玉米可以追溯到公元前5000年，特瓦坎洞穴年表为近三十年来玉米的进化提供了总体框架。 1989年，随着一种新形式的放射性碳测年法的应用，这种重建突然土崩瓦解。 标准的放射性碳方法需要大量的有机物质样品。 特瓦坎玉米样本太珍贵了，在20世纪60年代不能销毁，所以它们被间接地确定了年代--也就是说，通过使用来自同一地层的假定的碳。 加速器质谱仪（AMS）测年只需要有机物质的微量样品。 因此，玉米和其他植物的大型化石可以直接定年，消除了联合假设。 对特瓦坎古样本的重新研究表明，玉米在那里的出现时间比以前认为的要晚得多，而且地层学的关联性也不可信。 El Gigante的玉米样本与特瓦坎的玉米样本相当，包括人类利用的其他植物的碎片。它主要在2000 - 7000年前使用。因此，这个洞穴增加了对调查中美洲植物驯化起源有用的遗址的微薄名册。 在接下来的一年里，来自埃尔吉甘特的大约30个玉米和其他植物宏体化石样本，以及沿着的其他文化材料，如一个皮包，将通过AMS方法测定年代。 这些日期将测试地层学的可靠性，从而形成未来研究El Gigante集合的框架。 如果地层学是可信的，那么人类使用玉米和其他植物性食物长达5000年或更长时间的更好的图景将会出现。如果像特瓦坎那样，地层学是混乱的，那么我们将在很短的时间内-大约公元前2000-2500年-拥有无与伦比的古代迷宫人口。 这项研究的一个广泛影响将是为洞穴沉积物年代学意义的充分独立测试设定标准。 另一种方法是将注意力集中在中美洲的西南边缘，这一地区以前缺乏早期植物材料的分层沉积，这对于理解早期玉米从其有限的家园传播以及新世界粮食生产的传播这一更大的问题至关重要。