Introduction
Total Page：16
File Type：pdf, Size：1020Kb
INTRODUCTION It has been my privilege to work with more than 420 leading Quaternary scientists in developing the second edition of the Encyclopedia of Quaternary Science. This team of writers and editors represents 28 countries in Europe, Asia, Africa, the Americas, Australia, and New Zealand. Starting with the first edition in 2006, I have had my finger on the pulse of Quaternary science, and this branch of science is truly pulsating! Information now comes from an incredible variety of disciplines: geochemistry, numerical modeling, history, vulcanology, paleobiology, nuclear physics, stratigraphy, sedimentology, climatology, anthropology, archaeology, glacial geology, soil science, ice-stream modeling – the list is staggering. This highly disparate group of people are bound together by one common thread: the desire to know the history of the planet during the last 2.6 million years – the time of the ice ages. For Quaternary scientists, this is a pressing need, not an idle curiosity. Any doubts about this statement can be easily dispelled by a consideration of the lengths to which many of them go to gather the necessary data. Some of them have worked for months in sub-zero temperatures on top of very high mountains, or near the center of polar ice sheets, collecting ice cores. Others have spent many weeks on some of the roughest seas in the world, drilling deep-sea sediment cores. Often the work is more mundane. An oxygen isotope curve for a lengthy marine sediment core represents thousands of hours of patiently picking tiny fossils from layer after layer of sediments, in order to obtain sufficient numbers of calcium carbonate shells to yield samples for isotopic analysis. A map showing proposed ice limits from the last glaciation represents thousands of hours of field mapping of glacial features by dozens of people. Why do all of these people devote their lives to this pursuit of knowledge? Does it really matter so much? The answer becomes clear when you step back and examine the topic of Quaternary science in its proper context. The world we inhabit has largely been shaped by the events of the Quaternary. All the biological commu- nities that exist today are the end product of a long series of species associations that came together in the past, largely driven by climatic change during the Pleistocene. We cannot properly understand the functioning of modern ecosystems without a solid knowledge of their history, any more than we can understand the plot of a long novel by reading just the final page. We are also living in a time of alarming climate changes. Even though the pace and intensity of some of these changes have not been seen in historical times, there were many rapid, large-scale climatic shifts in the Pleistocene. The best way to predict the effects of global warming on the planet’s climate and ecosystems is to look at the history of similarly intense, rapid changes in the prehistoric past. The interval that is most relevant today is the most recent geologic period: the Quaternary. As human populations rise exponentially, increasing numbers of people are exposed to geologic hazards, such as earthquakes (and attendant tsunamis), and volcanic eruptions. These are short-lived events that take place only rarely in any one region. The interval between major events, such as volcanic eruptions, may be centuries or millennia. How do we come to grips with predicting the future likelihood of such erratic phenomena? Again, the answers come from piecing together the ancient history of such events, over many thousands of years. The Quaternary has been the time when our own species came of age. The beginning of the Quaternary, roughly 2.6 million years ago, was about the time when the earliest member of our genus (Homo) first appeared in Africa. Pleistocene environments shaped the course of human evolution, culminating in anatomically modern Homo sapiens spreading from Africa throughout most of the world during the last glaciation. Even though human beings largely shape their own environments today, for the vast majority of our species’ history, it has been the environment that has shaped us. Our direct ancestors’ adaptations to environmental change are deeply ingrained in our genes. Thus, an understanding of the environmental conditions that shaped our species is critical to our understanding of humanity. xi xii Introduction Quaternary science is a rapidly changing field, and the articles that appear in this encyclopedia reflect this. New dating techniques, such as cosmogenic nuclide dating, are revolutionizing our understanding of many earth surface processes. The ability to analyze increasingly smaller samples for radiocarbon and stable isotopes of oxygen and hydrogen means that we are gaining a level of precision in the reconstruction of past events that was unheard of just a few years ago. Stable isotope studies of air bubbles trapped in ice cores from Greenland and Antarctica have given Quaternary scientists an entirely new perspective on the rapidity and intensity of climatic change during the last glacial cycle and beyond. Likewise, the discovery of long sequences of annually laminated sediments in both marine and freshwater environments has provided a great leap forward in our ability to resolve the timing of environmental changes in nonpolar regions. The ability to extract and analyze ancient DNA sequences from Pleistocene fossils (both plants and animals) is revolutionizing the field of paleobiology. We are beginning to be able to trace the genetic lineages of a number of different organisms, from beetles to bison. In short, these are very exciting times to be a Quaternary scientist! While it is virtually impossible for any Quaternary researcher or student to keep abreast of all the new discoveries in this multifaceted science, this encyclopedia can be of great help. The articles contained here represent the state of the art in a huge variety of topics, and they offer the opportunity to dig deeper into their respective subjects by providing full citations of the most pertinent literature available. I invite you to come and explore the Quaternary Period in the pages that follow. It is a fascinating story. Scott A. Elias FOREWORD As with the publication of the first edition in 2007, the publication of the second edition of the Encyclopedia of Quaternary Science represents a landmark in the history of publishing in the field of Quaternary Science. Quaternary Science is a multidisciplinary endeavor which seeks to establish as detailed a picture as possible of the manifold environmental changes that have occurred during the most recent geological period, the Quaternary – an interval of time that spans the past 2.59 million years or the past 0.056% of geological time. It is a period of significant climate and environmental change and witnessed the widespread dispersal of our species, Homo sapiens, across the planet. Since Louis Agassiz and Reverend William Buckland traipsed over parts of the Scottish landscape in 1840 in search of evidence of glaciation, a huge literature has emerged on the science of long-term climate and environmental change. Rapid technological advances in the late twentieth century and the proliferation of scientific journals, particularly in an era of electronic publishing, have resulted in an exponential growth and documentation of knowledge on the climate and environmental changes that have occurred during the Quaternary period. More recently, there has been an increasing public interest in applied Quaternary research as a framework for understanding the basis for recent climate changes and for understanding the nature and frequency of geological hazards and vexing issues such as soil erosion and land degradation, and the adverse effects of ocean water temperature increases and acidification on coral reef environments. In a similar manner, the likely magnitude of future sea-level rise and the associated impacts on coastal landscapes in the twenty-first century have attracted wide public interest. In this sense, Quaternary Science is very much on the political agenda and is a critically important subject to address issues of public concern. The Encyclopedia of Quaternary Science edited by Scott Elias of Royal Holloway, University of London, UK, accordingly represents a particularly welcome addition to the literature. The encyclopedia presents an up-to- date and authoritative overview of Quaternary Science. The encyclopedia should enjoy a wide readership as the entries are presented in a very clear and easily readable style. The text of the articles is written at a level that allows undergraduate students to understand the material, while providing active researchers with a ready reference resource for information in the field. Each entry of up to 4000 words covers the salient points of each topic with very clear illustrations. A central theme that pervades the work is the importance of Quaternary Science in providing an historical context for assessing present environmental changes and as basis for modeling potential future changes. The encyclopedia consists of four volumes in print form and is available electronically. All the entries have been updated and the text totals around 3,500,000 words. As a major reference work, the encyclopedia has a very wide coverage of topics within the Quaternary sciences reflecting the complex and interdisciplinary nature of the science. Each of the major sections begins with a general overview of the topic prepared by a leading expert in the field. The major sections, for example, examine the analytical methods commonly used in paleoenvironmental reconstructions to unravel in a forensic-like manner the nature of former environments and the tempo of environmental change. Accordingly, a great range of topics such as the former extent of ice cover and nature of Quaternary glaciations, the biological responses and resultant fossil records to fluctuating climate, the expansion and contraction of desert environments, and global and local changes in relative sea levels are examined.