Abrupt global events in the Earth's history: a physics perspective

The timeline of the Earth's history reveals quasi-periodicity of the geological record over the last 542 Myr, on timescales close, in the order of magnitude, to 1 Myr. What is the origin of this quasi-periodicity? What is the nature of the global events that define the boundaries of the geological time scale? I propose that a single mechanism is responsible for all three types of such events: mass extinctions, geomagnetic polarity reversals, and sea-level fluctuations. The mechanism is fast, and involves a significant energy release. The mechanism is unlikely to have astronomical causes, both because of the energies involved, and because it acts quasi-periodically. It must then be sought within the Earth itself. And it must be capable of reversing the Earth's magnetic field. The last requirement makes it incompatible with the consensus model of the origin of the geomagnetic field - the hydromagnetic dynamo operating in the Earth's fluid core. In the second part of the paper, I show that a vast amount of seemingly unconnected geophysical and geological data can be understood in a unified way if the source of the Earth's main magnetic field is a ~200-km-thick lithosphere, repeatedly magnetized as a result of methane-driven oceanic eruptions, which produce ocean flow capable of dynamo action. The eruptions are driven by the interplay of buoyancy forces and exsolution of dissolved gas, which accumulates in the oceanic water masses prone to stagnation and anoxia. Polarity reversals, mass extinctions, and sequence boundaries are consequences of these eruptions. Unlike the consensus model of geomagnetism, this scenario is consistent with the paleomagnetic data showing that "directional changes during a [geomagnetic polarity] reversal can be astonishingly fast, possibly occurring as a nearly instantaneous jump from one inclined dipolar state to another in the opposite hemisphere".Comment: Final journal version. New title, significant changes. Supersedes v.

Heavy quarkonium: progress, puzzles, and opportunities

A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newly-found quarkonium-like states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K. Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D. Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A. Petrov, P. Robbe, A. Vair

A Numerical Study of Bubble Deformation in Steady Axisymmetric Flows

This work is devoted to the development and application of the numerical technique suitable for solution of the free-boundary problems, i.e. those in which the shape of the boundary should be determined as a part of the solution. The technique is based on a finite-difference solution of the equations of the problem on an orthogonal curvilinear coordinate system, which is also constructed numerically and always adjusted so as to fit the current boundary shape. The same orthogonal mapping approach may also be used to construct orthogonal coordinates fitted to boundaries of known but complicated shapes. The technique is applied to two classical problems of fluid mechanics -- deformation of a gas bubble rising through a quiescent fluid due to buoyancy, and deformation of a gas bubble in a uniaxial extensional flow. For the rising bubble, the shapes and flow fields are computed for Reynolds numbers 1 ≤ R ≤ 200 and Weber numbers up to 20 at the lower Reynolds numbers and up to 10 at Reynolds numbers 50, 100 and 200. The most interesting results of this part are those demonstrating the phenomenon of flow separation at a smooth free surface. This phenomenon does not appear to have been theoretically predicted before, in spite of its importance for understanding the mechanics of free-surface flows. In the case of a bubble in a uniaxial extensional flow, the computations show that at Reynolds numbers of order 10 and higher the deformation of a bubble proceeds in a way qualitatively different from the low Reynolds number regime studied previously; the bubble bursts at a relatively early stage of deformation never reaching the highly elongated shapes observed and predicted at low Reynolds numbers. It is shown also that for this problem the solution at Reynolds number of order 100 is already quite close to the potential flow solution which can be easily obtained using the present technique.</p