catastrophes and lesser calamities the causes of mass extinctions jul 2004

[...]... same applies to pandemics, such as the outbreak of influenza that swept through Europe and America in 1918, reaching the remote wastes of Alaska and the most isolated of island communities It is estimated that half the world’s population was infected, and that of those infected one in twenty died Most of In search of possible causes of mass extinctions 5 the fatalities were among teenagers and young adults... a mere 24 million years by the end of the nineteenth century With the discovery of radioactivity in rocks shortly afterwards, and the emergence of radiometric dating at the start of the twentieth century, this figure was quickly abandoned together with Kelvin’s theoretical assumptions The Earth’s age was then extended to hundreds of millions of years and then to a few thousand million years Lyell’s call... that the dinosaur joke was the only thing about them that he had remembered The other outcome is that, as a result of a short article I wrote repeating the story, two popular science books 4 In search of possible causes of mass extinctions Fig 1.1b Dinosaurs of the Cretaceous period have been published in the United States that attribute the authorship of the ‘constipation hypothesis’ to me As the. .. disturbed them The catastrophe that made these beds oblique had also thrust them above sea level Fossil species and even genera changed with the successive beds or strata In the middle of the marine beds there are other beds containing only terrestrial and freshwater plants or animals Thus the successive catastrophes of our planet have caused alternations of marine and terrestrial conditions The catastrophes. .. crater and the approximate location of the coastline at the end of the Cretaceous period (From A Hallam and P Wignall, Mass extinctions and their aftermath, Oxford University Press, 1997.) Fig 5.1 Photograph looking eastwards towards Lulworth Cove, Dorset, a county where the magnificent Jurassic and Cretaceous cliffs have been designated a World Heritage Site The rocks forming the headland consist of alternating... between the ‘solid’ beds, and attest to the force of the movements that these upheavals generated in the body of water Thus life on earth has often been disturbed by terrible events: calamities which initially perhaps shook the entire crust of the earth to a great depth, but which have since become steadily less deep and less general Living organisms without number have been the victims of these catastrophes. .. gymnosperms, at the expense of the flowering plants, the angiosperms Surviving gymnosperms, In search of possible causes of mass extinctions 3 Fig 1.1a Two dinosaurs of the Jurassic period which include cycads (palm-like trees) and conifers, commonly contain fluids with renowned purgative properties The implication, then, is that the herbivorous dinosaurs died of constipation The problem with this hypothesis... plains and stayed there peacefully for a long time At the feet of mountains, however, the strata become tilted, and the species they contain are different from those found in younger rocks These tilted beds form the crests of what in Cuvier’s time were called the ‘secondary mountains’, and plunge below the horizontal beds of hills that form their feet Some unspecified cause had broken, tilted, or otherwise... limestones and shales of the Lulworth Formation straddling the Jurassic–Cretaceous boundary, which were deposited in a marginal marine-to-lagoonal environment (These sediments are traditionally known as part of the Purbeck Beds.) They are overlain by soft-weathering silts, sands, and clays of the early Cretaceous Wealden Beds, also non-marine, into which the cove has been excavated by the sea They pass... selection The final demise of the dinosaurs would then have been the result, not of bad genes, but of bad luck, to use the laconic words of Dave Raup In contemplating the history of the dinosaurs it is necessary to rectify one widespread misconception Outside scientific circles the view is widely held that the dinosaurs lived for a huge slice of geological time little disturbed by their environment until the . alt="" Catastrophes and lesser calamities The causes of mass extinctions Tony Hallam is Emeritus Professor of Geology at the University of Birmingham and the author of a huge range of scientific. the authorship of the ‘constipation hypothesis’ to me . . . As the spread of an epidemic disease has so often been invoked for the extinction of the dinosaurs (and indeed of other groups), the. decline in the Cretaceous of the naked seed plants, or gymnosperms, at the expense of the flowering plants, the angiosperms. Surviving gymnosperms, 2 In search of possible causes of mass extinctions which