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The Cambrian Fossils of Chengjiang, China The Flowering of Early Animal Life von Xian-Guang, Hou (eBook)

  • Erscheinungsdatum: 09.03.2017
  • Verlag: Wiley-Blackwell
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The Cambrian Fossils of Chengjiang, China

The celebrated lower Cambrian Chengjiang biota of Yunnan Province, China, represents one of the most significant ever paleontological discoveries. Deposits of ancient mudstone, about 520 million years old, have yielded a spectacular variety of exquisitely preserved fossils that record the early diversification of animal life. Since the discovery of the first specimens in 1984, many thousands of fossils have been collected, exceptionally preserving not just the shells and carapaces of the animals, but also their soft tissues in fine detail. This special preservation has produced fossils of rare beauty; they are also of outstanding scientific importance as sources of evidence about the origins of animal groups that have sustained global biodiversity to the present day. Much of the scientific documentation of the Chengjiang biota is in Chinese, and the first edition of this book was the first in English to provide fossil enthusiasts with a comprehensive overview of the fauna. The second edition has been fully updated and includes a new chapter on other exceptionally preserved fossils of Cambrian age, exciting new fossil finds from Chengjiang, and a phylogenetic framework for the biota. Displaying some 250 figures of marvelous specimens, this book presents to professional and amateur paleontologists, and all those fascinated by evolutionary biology, the aesthetic and scientific quality of the Chengjiang fossils. Hou Xian-guang is former Director, Key Laboratory for Palaeobiology, Yunnan University, Kunming David J. Siveter is Professor Emeritus of Paleontology, University of Leicester Derek J. Siveter is Professor Emeritus of Earth Sciences, University of Oxford Richard J. Aldridge was Professor Emeritus and F.W. Bennett Professor of Geology, University of Leicester Cong Pei-yun is Professor of Paleobiology, Yunnan University, Kunming Sarah E. Gabbott is Professor of Paleobiology, University of Leicester Ma Xiao-ya is Professor of Paleobiology, Yunnan University, Kunming, and the Natural History Museum, London Mark A. Purnell is Professor of Paleobiology, University of Leicester Mark Williams is Professor of Paleobiology, University of Leicester

Produktinformationen

    Format: ePUB
    Kopierschutz: AdobeDRM
    Seitenzahl: 328
    Erscheinungsdatum: 09.03.2017
    Sprache: Englisch
    ISBN: 9781118896266
    Verlag: Wiley-Blackwell
    Größe: 145299 kBytes
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The Cambrian Fossils of Chengjiang, China

1
Geological Time and the Evolution of Early Life on Earth

Our planet is some 4540 million years old. We have little record of Earth's history for the first half billion years, but rocks have been found in Canada that date back some 4000 million years (Bowring & Williams 1999). There are yet older indications of the early Earth in the conglomerates of the Jack Hills of Australia, where tiny zircon crystals recycled from much older rocks give ages as old as 4400 million years (Wilde et al . 2001), and therefore their formation occurring a little after the birth of our planet. These zircons are important, because chemical signals within the crystals suggest the presence of water, a prerequisite for life on Earth, and also the lubricant for plate tectonics, which provides an active mineral and nutrient cycle to sustain life.

Because Earth's history is so enormous from a human perspective, it has been divided up into more manageable packets of time, comprising four eons, the Hadean, the Archean, the Proterozoic, and the Phanerozoic ( Fig. 1.1 ); the Hadean, Archean, and Proterozoic are jointly termed the Precambrian. In practice, the boundaries between these eons represent substantial changes in the Earth system driven by such components as plate tectonics, the interaction of life and the planet, and by the evolution of ever more complex biological entities. The boundary between the extremely ancient Hadean and Archean is set at about 4000 million years, whilst that between the Archean and Proterozoic is drawn at 2500 million years. The beginning of the Phanerozoic (literally meaning 'manifest life') is recognized by evolutionary changes shown by animals about 541 million years ago. The Archean is subdivided into the Eoarchaen (4000-3600 million years), the Paleoarchean (3600-3200 million years ago), the Mesoarchean (3200-2800 million years ago), and the Neoarchean (2800-2500 million years ago) eras. The Proterozoic is subdivided into the Paleoproterozoic (2500-1600 million years), the Mesoproterozoic (1600-1000 million years), and the Neoproterozoic eras (1000-541 million years). The earliest period of the Phanerozoic eon, the Cambrian, coined after the old Latin name for Wales, was a time that almost all of the major animal groups that we know on Earth today made their initial appearances in the fossil record. Some of the most important fossil evidence for these originations has come from the Chengjiang biota of southern China.

Figure 1.1 Some major events in the history of the Earth and early life.

However, the record of life on Earth goes back much further in time than the Cambrian Period, perhaps nearly as far as the record of the rocks. The early, Hadean Earth was subject to heavy bombardment by asteroids, many of which were so large that they would have vaporized early surface waters and oceans. This heavy bombardment ceased some 3900 million years ago, and from this period of the early Archean onwards there have been permanent oceans at the surface of planet Earth. Not long after - from a geological perspective - there is evidence for life. Microfossils of sulfur-metabolizing bacteria are reported from Paleoarchean rocks as old as 3400 million years in Australia (Wacey et al . 2011), and there is circumstantial evidence from geochemical studies that carbon isotopes were being fractionated by organic processes as long ago as 3860 million years in the Eoarchean (Mojzsis et al . 1996). However, there is a need to treat some of the reports of evidence for very early life with caution, and the further back in time the record is extended the more controversial the claims become (see, e.g., Grosch & McLouglin 2014).

The sparse organic remains of the Archean are microscopic and sometimes filamentous. But there is also macroscopic evidence for early life, represented by microbial mat

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