Dating the origin of modern humans
Published:January 01, 2001
One of the most serious past difficulties facing realistic tests of evolutionary models for modern human origins was the lack of widely applicable dating procedures that could reach beyond the practical limits of radiocarbon dating. Moreover, the amount of fossil material that had to be sacrificed to obtain a conventional radiocarbon date meant that human fossils could generally only be dated indirectly through supposedly associated materials. Because of these limitations, the transition from Neanderthals to modern humans in Europe was believed to have occurred about 35 000 radiocarbon years ago, but detailed reconstruction of the processes involved (for example, evolution or population replacement) was not practicable. In the Levant, the transition period from Neanderthals to modern humans was believed to lie only slightly beyond this 35 000-year watershed. Elsewhere, in Africa, east Asia and Australasia, the chronology for modern human origins was even more difficult to establish. However, over the last fifteen years, radiocarbon and non-radiocarbon physical dating techniques such as luminescence and electron spin resonance have been increasingly refined, leading to a revolution in our understanding of the timescale for human evolution, particularly for the last 200 000 years. Although each dating method has its own strengths and weaknesses, the picture that now emerges is one of a gradual evolution of Neanderthal morphology in Europe, in parallel with a similar evolution of modern humans in Africa. Modern humans also appear surprisingly early in the Levant (c. 100 ka ago) and Australia (c. 60 ka ago). However, many uncertainties still surround the process of establishment of our species globally.
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The Age of the Earth: From 4004 BC to AD 2002
The age of the Earth has long been a subject of great interest to scientists from many disciplines, particularly geologists, biologists, physicists and astronomers. This volume, The Age of the Earth: from 4004 BC to AD 2002, brings together contributors from these different subjects, along with historians, to produce a comprehensive review of how the Earth’s age has been perceived since ancient times. Touching on the works of eminent scholars from the seventeenth to nineteenth centuries, it describes how concepts of the Earth’s history changed as geology slowly separated itself from religious orthodoxy to emerge as a rigorous and self-contained science. Fossils soon became established as useful markers of relative age, while deductions made from geomorphological processes enabled the discussion of time in terms of years. By the end of the nineteenth century biologists and geologists were fiercely debating the issue with physicists who were unwilling to give them the time needed for evolution or uniformitarianism.
With the discovery of radioactivity, attempts to calculate the Earth’s age entered a new era, although these early pioneers in radiometric dating encountered many difficulties, both technical and intellectual, before the enormity of geological time was fully recognized. This effort affected both the theory and practice of geology. Geochronology was largely responsible for it maturing into a professional scientific discipline, as increasingly refined techniques measured not only the age of the rocks, but the rate of processes which now elucidate many aspects of the Earth’s evolution.
Even today the Earth’s chronology remains a contentious topic — particularly for those dating the oldest rocks — and it is implicated in debates surrounding our hominid ancestors, the origins and development of life, and the age of the universe.
The Age of the Earth: from 4004 bc to AD 2002 will be of particular interest to geologists, geochemists, and historians of science, as well as astronomers, archaeologists, biologists and the general reader with an interest in science.