Paleointensity of the early geodynamo (2.45 Ga) as recorded in Karelia: A single-crystal approach

Смирнов, А. В.; Tarduno, J. A.; Pisakin, B. N.

doi:10.1130/0091-7613(2003)031<0415:potegg>2.0.co;2

Cited by 60 publications

(47 citation statements)

References 27 publications

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“…The simulation with very small inner core, such as Earth is believed to have had one billion or more years ago, has an extraordinarily high O/E ratio, which also suggests a low Precambrian reversal rate. We note that currently available data do not indicate that the average field intensity was unusually high from 1 to 2.5 Ga [Macouin et al, 2003;Smirnov et al, 2003;Dunlop and Yu, 2004], but may indicate smaller contributions of even harmonics to the field around 2.5 Ga than from 0 -5 Ma [Smirnov and Tarduno, 2004]. Thus, symmetry of the timeaveraged field may prove to be a more robust predictor of reversal frequency than intensity.…”

mentioning

confidence: 67%

Symmetry and stability of the geomagnetic field

Coe¹,

Glatzmaier²

2006

Geophysical Research Letters

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Computer simulations of the geodynamo reveal a strong inverse correlation between stability and equatorial symmetry of the simulated field. This result is consistent with the paleomagnetically inferred degree of symmetry of Earth's magnetic field during the past 150 Ma, which reversed polarity more frequently when it was more symmetrical. A geodynamo simulation with solid inner core much smaller than it is today produced an exceptionally antisymmetric field, raising the possibility that reversals may have been much less common in the distant geologic past than more recently. Paleomagnetic evidence suggests that this might well be true.

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mentioning

confidence: 67%

Symmetry and stability of the geomagnetic field

Coe¹,

Glatzmaier²

2006

Geophysical Research Letters

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“…Subsequent refinements to techniques in palaeointensity (e.g. the single-crystal technique applied by Smirnov et al 2003) have generated mixed results, but several of the measurements indicate a strong field in the earliest Proterozoic (Fig. 1a).…”

Section: Evolution Of the Corementioning

confidence: 99%

“…Columns (a-t) are ordered to depict a general progression from core (left) to atmosphere (right). (a) Geodynamo strength from data reported by Smirnov (2003), Macouin et al (2004) and Shcherbakova et al (2008). (b) Average upper mantle adiabatic temperature curves from Richter (Richter 1988;Abbott et al 1994;Komiya 2004).…”

Section: Evolution Of the Corementioning

confidence: 99%

Palaeoproterozoic supercontinents and global evolution: correlations from core to atmosphere

Reddy

Evans

2009

115

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The Palaeoproterozoic era was a time of profound change in Earth evolution and represented perhaps the first supercontinent cycle, from the amalgamation and dispersal of a possible Neoarchaean supercontinent to the formation of the 1.9-1.8 Ga supercontinent Nuna. This supercontinent cycle, although currently lacking in palaeogeographic detail, can in principle provide a contextual framework to investigate the relationships between deep-Earth and surface processes. In this article, we graphically summarize secular evolution from the Earth's core to its atmosphere, from the Neoarchaean to the Mesoproterozoic eras (specifically 3.0-1.2 Ga), to reveal intriguing temporal relationships across the various 'spheres' of the Earth system. At the broadest level our compilation confirms an important deep-Earth event at c. 2.7 Ga that is manifested in an abrupt increase in geodynamo palaeointensity, a peak in the global record of large igneous provinces, and a broad maximum in several mantle-depletion proxies. Temporal coincidence with juvenile continental crust production and orogenic gold, massive-sulphide and porphyry copper deposits, indicate enhanced mantle convection linked to a series of mantle plumes and/or slab avalanches. The subsequent stabilization of cratonic lithosphere, the possible development of Earth's first supercontinent and the emergence of the continents led to a changing surface environment in which voluminous banded iron-formations could accumulate on the continental margins and photosynthetic life could flourish. This in turn led to irreversible atmospheric oxidation at 2.4-2.3 Ga, extreme events in global carbon cycling, and the possible dissipation of a former methane greenhouse atmosphere that resulted in extensive Palaeoproterozoic ice ages. Following the great oxidation event, shallow marine sulphate levels rose, sediment-hosted and iron-oxide-rich metal deposits became abundant, and the transition to sulphide-stratified oceans provided the environment for early eukaryotic evolution. Recent advances in the geochronology of the global stratigraphic record have made these inferences possible. Frontiers for future research include more refined modelling of Earth's thermal and geodynamic evolution, palaeomagnetic studies of geodynamo intensity and continental motions, further geochronology and tectonic syntheses at regional levels, development of new isotopic systems to constrain geochemical cycles, and continued innovation in the search for records of early life in relation to changing palaeoenvironments.

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“…Some reviews of Precambrian palaeointensity (e.g. Prévot and Perrin, 1992;Smirnov et al, 2003;Dunlop and Yu, 2004) have concluded that there is little evidence for any long term trend in mean geomagnetic intensity. Conversely, Macouin et al (2004) argued for a long-term increase of dipole moment and in particular, a 'significant increase' initiated some time between 1000 and 300 Ma.…”

Section: Introductionmentioning

confidence: 99%

The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database

2009

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We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia. These results were severely affected by magnetomineralogical alteration occurring during the laboratory heating process necessitating the application of a correction procedure. The correction allowed results from three lavas to pass strict selection criteria but we deem that only one of these exhibits sufficient internal consistency to be considered moderately reliable. It yields a virtual dipole moment of 47±6 ZAm 2 which is 60% of the present-day value. We combine this determination with a filtered dataset from the updated IAGA (International Association of Geomagnetism and Aeronomy) palaeointensity database, PINT08. Directional secular variation has recently been shown to have changed fundamentally since the Archaean, probably as a consequence of inner core growth since that time. However, here we argue that it is still unclear whether this evolution was accompanied by a single long timescale change in average poloidal field intensity. While the distribution of Precambrian palaeointensity determinations as a whole is significantly lower than that for the last 300 Myr, we show that this finding largely reflects data from the Proterozoic aeon. The distribution of more ancient measurements from the late Archaean-earliest Proterozoic is indistinguishable from that of the last 300 Myr which might suggest that a 'Proterozoic dipole low' period existed between two periods of higher field intensity. Were this pattern of long-term geomagnetic intensity variation to be supported by the addition of new data in the future, then it could indicate a related three-stage evolution in core dynamics, namely: vigorous thermal convection caused by high core-mantle heat flux early in the Earth's history, weaker thermal convection later as the heat flux fell, and finally, strong compositional convection since the inner core nucleated.

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Paleointensity of the early geodynamo (2.45 Ga) as recorded in Karelia: A single-crystal approach

Cited by 60 publications

References 27 publications

Symmetry and stability of the geomagnetic field

Symmetry and stability of the geomagnetic field

Palaeoproterozoic supercontinents and global evolution: correlations from core to atmosphere

The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database

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