When in 1981 Louis and Walter Alvarez, the father and son team, unearthed a tell-tale Iridium-rich sedimentary horizon at the 65 million years-old Cretaceous-Tertiary boundary at Gubbio, Italy, their find heralded a paradigm shift in the study of terrestrial evolution. Since the 1980s the discovery and study of asteroid impact ejecta in the oldest well-preserved terrains of Western Australia and South Africa, by Don Lowe, Gary Byerly, Bruce Simonson, Scott Hassler, the author and others, and the documentation of new exposed and buried impact structures in several continents, have led to a resurgence of the idea of the catastrophism theory of Cuvier, previously largely supplanted by the uniformitarian theory of Hutton and Lyell. Several mass extinction of species events are known to have occurred in temporal proximity to large asteroid impacts, global volcanic eruptions and continental splitting. Likely links are observed between asteroid clusters and the 580 Ma acritarch radiation, end-Devonian extinction, end-Triassic extinction and end-Jurassic extinction. New discoveries of ~3.5 – 3.2 Ga-old impact fallout units in South Africa have led Don Lowe and Gary Byerly to propose a protracted prolongation of the Late Heavy Bombardment (~3.95-3.85 Ga) in the Earth-Moon system. Given the difficulty in identifying asteroid impact ejecta units and buried impact structures, it is likely new discoveries of impact signatures are in store, which would further profoundly alter models of terrestrial evolution. .

This book presents a comprehensive overview of Australian impact structures and related mineralization, including a discussion of the significance of many of these structures for crustal evolution. The book focuses in particular on Archaean impact ejecta/fallout units in the Pilbara Craton of Western Australia, large exposed and buried impact structures, and on the geophysical evidence for possible to probable impact structures. Thanks to their long-term geological stability, Precambrian and younger terrains in the Australian continent contain 38 confirmed impact structures and 43 ring and dome structures, many of which constitute possible to probable asteroid impact structures. The impact structures have been the subject of more than half a century of studies and range from several tens of meter-large craters to buried structures larger than 100 km in diameter. Discoveries of impact fallout units in the Pilbara Craton have defined the Pilbara as one of the two best documented terrains where Archaean impact ejecta/fallout deposits are identified, the other terrain being the Kaapvaal Craton in southern Africa. A synthesis of evidence from both cratons indicates periods of large asteroid bombardments during ~3.47 – 2.48 billion years-ago, including peak bombardment about 3.25—3.22 billion years-ago. The latter period coincides with an abrupt transformation of an early Archaean granite-greenstone crust to mid to late Archaean semi-continental crustal regimes, underpinning the significance of heavy asteroid impact events for crustal evolution. Apart from proven impact structures, Australian terrains display a range of circular features, including morphological and drainage rings, circular lakes, volcanic craters, tectonic domes, oval granite bodies, mafic igneous plugs, salt diapirs, and magnetic, gravity and seismic anomalies, many of which are of a likely impact origin. Thermal and hydrothermal processes associated with impact cratering bear important consequences for the formation of mineral deposits, such as Ni at Sudbury, Pb-Zn at Siljan and Kentland. Impact structures may also provide sites for the accumulation of hydrocarbons, whereas in some instances fracturing associated with impact structures allows outward migration of oil and gas.

In this volume, the geologic and planetary science communities explore impact events and how they affected the evolution of Earth and other planetary bodies. these papers are the outcome of a conference held every five years.

Comprises 28 papers which grew out of the International Conference on Large Meteorite Impacts and Planetary Evolution, August/September, 1992 in Sudbury, Ontario. The interdisciplinary papers, encompassing diverse studies from trace element geochemistry to planetary exploration, are arranged into f

Most scientists now agree that some sixty-five million years ago, an immense comet slammed into the Yucatan, detonating a blast twenty million times more powerful than the largest hydrogen bomb, punching a hole ten miles deep in the earth. Trillions of tons of rock were vaporized and launched into the atmosphere. For a thousand miles in all directions, vegetation burst into flames. There were tremendous blast waves, searing winds, showers of molten matter from the sky, earthquakes, and a terrible darkness that cut out sunlight for a year, enveloping the planet in freezing cold. Thousands of species of plants and animals were obliterated, including the dinosaurs, some of which may have become extinct in a matter of hours. In Impact, Gerrit L. Verschuur offers an eye-opening look at such catastrophic collisions with our planet. Perhaps more important, he paints an unsettling portrait of the possibility of new collisions with earth, exploring potential threats to our planet and describing what scientists are doing right now to prepare for this awful possibility. Every day something from space hits our planet, Verschuur reveals. In fact, about 10,000 tons of space debris fall to earth every year, mostly in meteoric form. The author recounts spectacular recent sightings, such as over Allende, Mexico, in 1969, when a fireball showered the region with four tons of fragments, and the twenty-six pound meteor that went through the trunk of a red Chevy Malibu in Peekskill, New York, in 1992 (the meteor was subsequently sold for $69,000 and the car itself fetched $10,000). But meteors are not the greatest threat to life on earth, the author points out. The major threats are asteroids and comets. The reader discovers that astronomers have located some 350 NEAs ("Near Earth Asteroids"), objects whose orbits cross the orbit of the earth, the largest of which are 1627 Ivar (6 kilometers wide) and 1580 Betula (8 kilometers). Indeed, we learn that in 1989, a bus-sized asteroid called Asclepius missed our planet by 650,000 kilometers (a mere six hours), and that in 1994 a sixty-foot object passed within 180,000 kilometers, half the distance to the moon. Comets, of course, are even more deadly. Verschuur provides a gripping description of the small comet that exploded in the atmosphere above the Tunguska River valley in Siberia, in 1908, in a blinding flash visible for several thousand miles (every tree within sixty miles of ground zero was flattened). He discusses Comet Swift-Tuttle--"the most dangerous object in the solar system"--a comet far larger than the one that killed off the dinosaurs, due to pass through earth's orbit in the year 2126. And he recounts the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994, as some twenty cometary fragments struck the giant planet over the course of several days, casting titanic plumes out into space (when Fragment G hit, it outshone the planet on the infrared band, and left a dark area at the impact site larger than the Great Red Spot). In addition, the author describes the efforts of Spacewatch and other groups to locate NEAs, and evaluates the idea that comet and asteroid impacts have been an underrated factor in the evolution of life on earth. Astronomer Herbert Howe observed in 1897: "While there are not definite data to reason from, it is believed that an encounter with the nucleus of one of the largest comets is not to be desired." As Verschuur shows in Impact, we now have substantial data with which to support Howe's tongue-in-cheek remark. Whether discussing monumental tsunamis or the innumerable comets in the Solar System, this book will enthrall anyone curious about outer space, remarkable natural phenomenon, or the future of the planet earth.

Earth as an Evolving Planetary System, Second Edition, explores key topics and questions relating to the evolution of the Earth's crust and mantle over the last four billion years. This updated edition features exciting new information on Earth and planetary evolution and examines how all subsystems in our planet—crust, mantle, core, atmosphere, oceans and life—have worked together and changed over time. It synthesizes data from the fields of oceanography, geophysics, planetology, and geochemistry to address Earth's evolution. This volume consists of 10 chapters, including two new ones that deal with the Supercontinent Cycle and on Great Events in Earth history. There are also new and updated sections on Earth's thermal history, planetary volcanism, planetary crusts, the onset of plate tectonics, changing composition of the oceans and atmosphere, and paleoclimatic regimes. In addition, the book now includes new tomographic data tracking plume tails into the deep mantle. This book is intended for advanced undergraduate and graduate students in Earth, Atmospheric, and Planetary Sciences, with a basic knowledge of geology, biology, chemistry, and physics. It also may serve as a reference tool for structural geologists and professionals in related disciplines who want to look at the Earth in a broader perspective. - Kent Condie's corresponding interactive CD, Plate Tectonics and How the Earth Works, can be purchased from Tasa Graphic Arts here: http://www.tasagraphicarts.com/progptearth.html - Two new chapters on the Supercontinent Cycle and on Great Events in Earth history - New and updated sections on Earth's thermal history, planetary volcanism, planetary crusts, the onset of plate tectonics, changing composition of the oceans and atmosphere, and paleoclimatic regimes - Also new in this Second Edition: the lower mantle and the role of the post-perovskite transition, the role of water in the mantle, new tomographic data tracking plume tails into the deep mantle, Euxinia in Proterozoic oceans, The Hadean, A crustal age gap at 2.4-2.2 Ga, and continental growth