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Figure 4.7 Climatic megacycles during the Phanerozoic. The hothouse-icehouse cycle has a period of about 300 million years the warm-mode-cool-mode cycle has a period of about 150 million years. Notice that the two cycle 'conflict' at times. For instance, cool modes during the hothouse phase prevailing during the Late Cambrian, Ordovician, Silurian, and Devonian, and during the hothouse phase prevailing during the Jurassic, Cretaceous, and Late Eocene. Sources Hothouses and icehouses adapted...

Giant tsunamis

Storm surges and tsunamis both produce short-lived, severe inundations of coasts by marine waters, witness the Indian Ocean tsunami of 26 December 2004. Storm surges and tsunamis leave lithic or bioclastic sediment (or both) deposits above the highest astronomical tide (Plates 5.1-5.3) (Chappell et al. 1983 Atwater 1987 Bryant et al. 1992 Dawson 1994). Smaller tsunamis cause run-up and backwash, and leave traces in coastal regions (see Dawson 1994). For instance, tsunamis generated by the...

Macroevolution versus microevolution

Macroevolution encompasses a variety of patterns and processes involving species and larger clades. Some of these patterns can plausibly be described as the result of microevolutionary processes extended across the great expanses of time and space provided by the fossil record. . . . But discontinuities have been documented at a variety of scales, from the punctuated nature of much speciation, to patterns of community overturn, the sorting of species within clades by differential speciation and...

What caused the last ice age

This is a hotly (or perhaps that should be coldly) disputed question. Over the past 50 million years, the Earth's climate has cooled. Large ice sheets formed on Antarctica 35 million years ago, but did not form in the Northern Hemisphere until about 2.7 million years ago. Earth scientists mostly agree that global climatic cooling is associated with decreasing levels of carbon dioxide in the atmosphere. They also generally agree that ice sheets grow only if sufficient moisture is available to...

The bombardment hypothesis

The bombardment hypothesis has its roots in explanations for stones falling from the heavens. From earliest times until the start of the nineteenth century, it was widely believed that some types of stone grew in the air and fell from the skies, notably on dark nights and during storms (see Marvin 1986, for a review). The oldest known report of a stone falling from the sky comes from China in 644 BC. Pliny the Elder (AD 23-79), in his NaturalisHistoria, distinguished four classes of stone, the...

Stasis and change

If strict Darwinists were to be believed, the history of life is an uninterrupted sequence of species turnover, with species incessantly appearing and disappearing as creatures either adapt to changing physical environments and ever-shifting competition, evolve into new species, or go extinct. No coordination is involved - species appear and disappear independently of each other through time. However, some palaeontologists have found evidence that the history of life is not always an...

Contraction and expansion tectonics

Earth Outlines

A long-running debate concerns the change in size of the solid Earth - has it stayed the same, shrunk, or swollen A steady-state view, in which the Earth has had constant dimensions, is associated with the ruling plate-tectonic theory and with fixed continents and oceans model (e.g. Meyerhoff and Meyerhoff 1972). Proposals of an expanding or contracting globe are controversial but not without foundation. Earth contraction, once regarded as a good explanation of tectonic episodes, is no longer...

Micromutations or macromutations

Micromutations - small genetic changes - are the bread-and-butter of neo-Darwinists and supporters of the synthetic theory, who see them as the basis of speciation. Believers in macromutations take a very different view of speciation. A macromutation is a drastic reorganization of the genotype that, in an extreme case, would produce a new species in a sin gle step - a saltation or jump. It thus introduces discontinuity into the evolutionary process and is a true punctuational event. If...

Oceanic overspill

The original 1970s models of the connection between the Mediterranean Sea and the Black Sea considered that the bedrock sill through the Bosporus Strait, over which water could flow, was shallow. While the outlet was active, the Black Sea followed the rises and falls of global sea-level. Whenever global sea level fell below the Bosporus outlet, it was assumed that the Black Sea stabilized at the outlet level, as any water loss was replenished by in-draining rivers. During the 1980s, researchers...

Impact craters

Since 1946, convincing, if not totally unequivocal, evidence for the impact origin of many terrestrial craters has been unearthed. Evidence comes from at and near the crater site itself, and from material ejected from the crater and broadcast far and wide. The evidence at the crater itself takes the form of three different, though related, signatures of impacts shatter cones, shock-metamorphosed forms of silica (coesite and stishovite), and shocked quartz crystals. All of these features...

The eventful ice age

Two key questions arise from the study of the Quaternary ice age Why was it so eventful, displaying alternations between glacial and interglacial stages and stadial and interstadial shifts And, what caused it The jostling of the planets, their satellites, and the Sun leads to medium-term orbital variations occurring with periods in the range 10,000 to 500,000 years that perturb Earth's climate. These orbital forcings do not change the total amount of solar energy received by the Earth during...

Impact superfloods

The scale of flooding unleashed by a large asteroid or comet crashing into the ocean would dwarf all the above superfloods. The gigantic waves thrown up by bombardment would produce floods that could truly be called super (Huggett 1989a, 1989b). Earth-crossing asteroids and comets possess enormous kinetic energy. Should they crash into the ocean, they would create an enormous wave system that would flood continental lowlands (Figure 5.4 see also Hills et al. 1994). Tolerably firm sedimentary...

Lake outbursts

The catastrophic release of impounded water in smallish glacial lakes creates medium-scale geomorphic features. The Watrous spillway, Saskatchewan, Canada, rapidly incised during a short-lived outburst from glacial Lake Elstow Kehew and Teller 1994 . In its outlet area, the bed of Lake Elstow was composed of stagnant ice. The 40-km-long spillway cuts across a divide, and ends in the glacial Last Mountain Lake basin, where a coarse-grained fan was deposited. Large clasts are concentrated on the...

V

Reflection by polar S snow and ice cover Reflection by tropical convective clouds Figure 9.3 Conceptual diagrams of top planetary albedo and bottom land surface albedo versus surface temperature and evapotranspiration, respectively. Source Reprinted with kind permission of Springer Science and Business Media from A. Kleidon and K. Fraedrich 2004 Biotic entropy production and global atmosphere-biosphere interactions. In A. Kleidon and R. D. Lorenz eds Non-equilibrium Thermodynamics and the...

Diversity cycles

The diversity life has fluctuated through the Phanerozoic with the fossil record yielding up tantalizing suggestions of periodicity. Researchers claim to have teased out cycles of varying length using varied information, including diversity, first and last appearances, and extinction and origination rates. Early work on marine data hinted at a 30-million-year cycle Fischer 1984 that expresses itself in the global diversity of planktonic and nektonic taxa, including globigerinacean foraminifers...

The Gaia hypothesis

Life wields a potent influence on the composition of the atmosphere composition, producing a chemical disequilibrium, as seen in the high concentration of reactive atmospheric oxygen. Photosynthesis sustains this chemical disequilibrium by releasing oxygen and removing carbon dioxide from the air. It occurred to James Lovelock 1965 , an atmospheric chemist, that such a non-equilibrium atmospheric state would be a guide to the presence of life on other planets see also Hitchcock and Lovelock...

Plate tectonics

Antarctic Plate And Australian Plate

The idea of lithospheric plates Figure 2.2 emerged with the acceptance of continental drift. If the continents have drifted, as Alfred Lothar Wegener 1915 claimed, then large chunks of crust including continental cratons and deep ocean basins have travelled several thousand kilometres without having suffered any appreciable lateral distortion. Two features indicate this lack of distortion. First, is the excellent 'fit' of the opposing South American and African coastlines, which have taken 200...

Acknowledgements

I should like to thank the usual suspects who have made the completion of this book possible Nick Scarle for drawing the diagrams Andrew Mould for taking on board a 'research monograph' with limited sales potential Anja Scheffers for kindly letting me use her photographs and the University of Manchester for granting me a semester's research leave. As always, special thanks go to my wife, and to my two youngest children for letting me use my PC between sessions of Battle for Middle-Earth,...

Plume tectonics

Oceanic Lithosphere Composition

The reassessment of the mantle plume hypothesis has become the most exciting current debate in Earth science Foulger 2005 . To appreciate the dynamics of the debate, it is useful to consider the mantle plume model before exploring the reasons for its possible demise and replacement with a plate model. Mantle plumes may start growing the core-mantle boundary. The mechanisms by which they form and grow are undecided. They may involve rising plumes of liquid metal and light elements pumping latent...

Debates and the geosphere

For many centuries, the bowels of the Earth were a matter of intense conjecture with little evidence against which to assess the worth of rival ideas. For some time after the Renaissance, most scholars accepted the system proposed by Empedocles and elaborated by Aristotle, which maintained that there were four elements - air, earth, fire, and water. They believed that the Earth was a solid, spherical body composed of assorted metals, rocks, and earth, within which were underground regions of...

Debates and the biosphere

Evolutionary theory began with Charles Darwin and Alfred Russel Wallace. The key arguments of their joint 1858 paper were, briefly all organisms produce more offspring than their environment can support abundant variations of most characters occur within species competition of limited resources creates a struggle for life or existence descent with heritable modification occurs and, in consequence, new species evolve Kutschera and Niklas 2004 . Neo-Darwinism began when August Weismann 1892...

The tempo of evolution

The fossil record yields up evidence of evolution. A big debate surrounds the pattern of evolution - is it slow and stately gradualism or does it proceed by rapid change followed by periods of stasis punctuated equilibrium . Gradualism versus punctuated equilibrium Othenio Abel 1929 and George Gaylord Simpson 1953 distinguished between phyletic change anagenesis and phylogenetic change speciational change or cladogenesis . Phyletic change occurs within a single lineage, whereas phylogenetic...