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.

Heme Oxygenase-1 Accelerates Cutaneous Wound Healing in Mice

Heme oxygenase-1 (HO-1), a cytoprotective, pro-angiogenic and anti-inflammatory enzyme, is strongly induced in injured tissues. Our aim was to clarify its role in cutaneous wound healing. In wild type mice, maximal expression of HO-1 in the skin was observed on the 2nd and 3rd days after wounding. Inhibition of HO-1 by tin protoporphyrin-IX resulted in retardation of wound closure. Healing was also delayed in HO-1 deficient mice, where lack of HO-1 could lead to complete suppression of reepithelialization and to formation of extensive skin lesions, accompanied by impaired neovascularization. Experiments performed in transgenic mice bearing HO-1 under control of keratin 14 promoter showed that increased level of HO-1 in keratinocytes is enough to improve the neovascularization and hasten the closure of wounds. Importantly, induction of HO-1 in wounded skin was relatively weak and delayed in diabetic (db/db) mice, in which also angiogenesis and wound closure were impaired. In such animals local delivery of HO-1 transgene using adenoviral vectors accelerated the wound healing and increased the vascularization. In summary, induction of HO-1 is necessary for efficient wound closure and neovascularization. Impaired wound healing in diabetic mice may be associated with delayed HO-1 upregulation and can be improved by HO-1 gene transfer

Modulation of the Shubnikov-de Haas Oscillations by the Exchange Interaction in Cd3−x−y\text{}_{3-x-y}Znx\text{}_{x}Mny\text{}_{y}As2\text{}_{2}

New measurements of the Shubnikov-de Haas (SdH) effect in semimagnetic semiconductor (SMSC) Cd$\text{}_{3-x-y}$Zn$\text{}_{x}$Mn$\text{}_{y}$As$\text{}_{2}$ with x = 0.09 and y = 0.018, using continuous magnetic fields up to 25 T, are presented. The observed modulation of the amplitudes of the first and second SdH harmonics as a function of magnetic field is interpreted in terms of the three band Kane model with the exchange interaction included and taking into account the spin-dependent scattering which appears to be particularly important at high magnetic fields

Anisotropy of the Exchange Interaction in Mn-Alloyed II3\text{}_{3}-V2\text{}_{2} Compounds

An anisotropy of the electron effective g-factor in highly degenerated tetragonal semimagnetic semiconductors (SMSC) alloyed with manganese has been found by us and by other workers when studying the Shubnikov-de Haas (SdH) effect for different orientations of the magnetic field with respect to the crystal axes. The detailed analysis of the experimental data by using a model based on an infinite Hamiltonian matrix, provides evidence for the anisotropy of the p-d exchange interaction in the materials of interest

Influence of Pressure on Magnetization of (Cd1−x−y\text{}_{1-x-y}Zny\text{}_{y}Mnx\text{}_{x})3\text{}_{3}As2\text{}_{2}

The influence of hydrostatic pressure up to 0.6 GPa on magnetization of (Cd$\text{}_{1-x-y}$Zn$\text{}_{y}$Mn$\text{}_{x}$)$\text{}_{3}$As$\text{}_{2}$ with various compositions was studied at 4.2 K and in magnetic fields up to 7 T. The obtained experimental data were analysed within our generalized pair approximation model, treating the total Mn-Mn interaction strength as a sum of superexchange and the Bloembergen-Rowland exchange. As a result, we obtained satisfactory agreement between our approach and experiment by introducing a pressure dependence of p-d hybridization potential V$\text{}_{pd}$ in the form V$\text{}_{pd}$ ∝ d$\text{}^{-4}$, where d is the Mn-As bond length which decreases with pressure

Magnetic Specific Heat of (Cd1−x−y\text{}_{1-x-y}Zny\text{}_{y}Mnx\text{}_{x})3\text{}_{3}As2\text{}_{2}

The specific heat of (Cd$\text{}_{1-x-y}$Zn$\text{}_{y}$Mn$\text{}_{x}$)$\text{}_{3}$As$\text{}_{2}$ with low Mn concentration (x ≤ 0.067) and for two Zn contents (y = 0.14 and y = 0.34) has been measured in the temperature range of 1.5-30 K. The magnetic contribution to the total specific heat has been analysed within our generalized pair approximation model which takes into account the complicated tetragonal crystal structure of Cd$\text{}_{1-x-y}$Zn$\text{}_{y}$Mn$\text{}_{x}$)$\text{}_{3}$As$\text{}_{2}$. Assuming that the total Mn-Mn interaction strength is a sum of superexchange and the Bloembergen-Rowland exchange, we have obtained a very good agreement between our approach and experiment by using the analytical formulae with only two adjustable parameters, i.e. the first nearest-neighbour exchange constants for both mechanisms which appear to be strongly dependent on Zn content

Spectroscopic Properties of Pr3+Pr^{3+} Ion in Various Tellurite Glasses

The goal of this work was to investigate the spectroscopic properties of $Pr^{3+}$ ions (of a comparable concentration of the order of 0.2 mol/dm³) embedded in the tellurite glass matrix, i.e. $TeO_2-WO_3-PbO$ modified with lanthanum and lutetium oxides. The difference is that the last components of both glasses provide ions which are optically inactive within the 4f shell, since this shell is completely empty for $La^{3+}$ ion and completely filled for $Lu^{3+}$ ion. The absorption and fluorescence spectra of $Pr^{3+}$ doped in tellurite glass has been recorded and analyzed in terms of the Judd-Ofelt theory. The studies of the glasses comprised ellipsometric, spectrophotometric and photoluminescence measurements. The ellipsometric studies yield the refraction index dispersion which appears to be quite similar for all the studied glasses. From the spectrophotometric measurements, the absorption spectra have been obtained which, for $Pr^{3+}$-doped samples, have been analyzed in terms of the Judd-Ofelt theory. Finally, the photoluminescence studies demonstrate a clear visible emission from $\text{}^3P_0$ level to lower-lying states of $Pr^{3+}$ ion