INVESTIGATING THE NATURE AND TIMING OF THE EARLIEST HUMAN OCCUPATION OF NORTH AMERICA USING A NOVEL INTEGRATION OF BIOGEOCHEMISTRY AND MICROMORPHOLOGY

点击翻译按钮获取中文摘要

How, when and why did people first arrive and settle in the Americas? This puzzle is one that has captured scientific and public imagination, and is the subject of continued debate. The traditional model of 'Clovis First' asserts that the Clovis culture, named after their distinctive stone tools found near Clovis, New Mexico, in the 1920s and 1930s, arrived on the continent around 13,500 BP. These people would have travelled across the Beringia land bridge in Siberia, during a time when sea levels were lowered during the last ice age, and eventually made their way south on the east side of the Rocky Mountains. Recently a growing body of evidence points to a more complex process, with perhaps several waves of migration of different cultural groups. This has led to a situation where there is no consensus on how humans first came to the Americas. The main barrier to addressing this debate, is the scarcity of well-preserved sites and easily datable materials, where we can be sure that what we are dating really does represent human presence. Human skeletal remains from this period are especially rare, and also incredibly difficult to study due to restrictions of the Native American Graves Protection and Repatriation Act 1990 (NAGPRA). However, a more unusual form of archaeological evidence are well preserved in caves: fossilized human faeces, or coprolites. One of the most famous prehistoric coprolites, is a specimen from Paisley Caves, Oregon, dated 14,300 BP; one thousand years earlier than evidence from the Clovis culture. This coprolite is strong evidence for the 'Pre-Clovis' occupation of North America. The coprolite was identified as human on the basis of ancient DNA, but there have been debates over the stratigraphic integrity. This is a problem which continues to underlie much research in this area. We simply do not know the extent to which these molecules are mobile within cave sediments. This is the missing scientific link which prevents the coprolites from being used, unambiguously, to confirm the pre-Clovis hypothesis and solve this long running debate. Our research will make a first attempt to address these problems, by using a novel integration of biogeochemistry and sediment micromorphology - a method successfully developed by the PI and Co-I. Sediment micromorphology can be thought of as an excavation under the microscope. Intact blocks of archaeological sediments are set in resin and turned into slides for viewing under a microscope. This way we can visually examine the processes by which sediments have been deposited, and whether they have been subsequently altered. Combining this with biogeochemical analysis of faecal lipids will enable us to quantify the extent to which these molecules move from their point of deposition . We will conduct this analysis in conjunction with radiocarbon dating of specific chemical fractions - rather than dating all the organic material in a sample, we will date individual chemical fractions within the coprolites. This way we can provide a firm species identification, and simultaneously an unambiguous date for when the coprolite was deposited. Whoever these early settlers were, these unlikely sources of evidence that they left behind contain a wealth of information which we can now access using the novel techniques proposed in this research project. Once we can demonstrate the integrity of the coprolite materials found in the cave and therefore have confidence in the scientific data we obtain from them, we can use the molecules and fossils preserved with the coprolites to reconstruct the diets of these individuals, and the environment they inhabited. By linking this with high resolution radiocarbon dating, we can begin to extend the research potential to look at other questions of scientific and archaeological interest such as the seasonality of cave use; what relationship did these early settlers have with the environment, and how did they utilise the resources available to them?