Reassessing evidence of Moon–Earth dynamics from tidal bundles at 3.2 Ga (Moodies Group, Barberton Greenstone Belt, South Africa)

Past orbital parameters of the Moon are difficult to reconstruct from geological records because relevant data sets of tidal strata are scarce or incomplete. The sole Archean data point is from the Moodies Group (ca 3.22 Ga) of the Barberton Greenstone Belt, South Africa. From the time-series analysis of tidal bundles from a well-exposed subaqueous sand wave of this unit, Eriksson and Simpson (Geology, 28, 831) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although this study’s detailed geological mapping and section measuring of the site confirmed that the sandstone bed in question is likely a migrating dune, the presence of angular mud clasts, channel-margin slumps, laterally aggrading channel fills and bidirectional paleocurrents in overlying and underlying beds suggests that this bedform was likely located in a nearshore channel near lower-intertidal flats and subtidal estuarine bars; it thus carries risk of incomplete preservation. Repeated measurements of foreset thicknesses along the published traverse, measured perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along traverses measured parallel to bedding along the 20.5 m wide exposure are affected by minor faulting, uneven outcrop weathering, changing illumination, weather, observer bias and show a low reproducibility. The most robust measurements herein confirm the periodicity peak of approximately 14 in the original data of Eriksson and Simpson (Geology, 28, 831). Because laminae may have been eroded, the measurements may represent a lower bound of about 28 lunar days per synodic month. This estimate agrees well with Earth–Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a lower orbit around a faster-spinning Earth

Reassessing evidence of Moon–Earth dynamics from tidal bundles at 3.2 Ga (Moodies Group, Barberton Greenstone Belt, South Africa)

Past orbital parameters of the Moon are difficult to reconstruct from geological records because relevant data sets of tidal strata are scarce or incomplete. The sole Archean data point is from the Moodies Group (ca 3.22 Ga) of the Barberton Greenstone Belt, South Africa. From the time-series analysis of tidal bundles from a well-exposed subaqueous sand wave of this unit, Eriksson and Simpson (Geology, 28, 831) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although this study’s detailed geological mapping and section measuring of the site confirmed that the sandstone bed in question is likely a migrating dune, the presence of angular mud clasts, channel-margin slumps, laterally aggrading channel fills and bidirectional paleocurrents in overlying and underlying beds suggests that this bedform was likely located in a nearshore channel near lower-intertidal flats and subtidal estuarine bars; it thus carries risk of incomplete preservation. Repeated measurements of foreset thicknesses along the published traverse, measured perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along traverses measured parallel to bedding along the 20.5 m wide exposure are affected by minor faulting, uneven outcrop weathering, changing illumination, weather, observer bias and show a low reproducibility. The most robust measurements herein confirm the periodicity peak of approximately 14 in the original data of Eriksson and Simpson (Geology, 28, 831). Because laminae may have been eroded, the measurements may represent a lower bound of about 28 lunar days per synodic month. This estimate agrees well with Earth–Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a lower orbit around a faster-spinning Earth

Laser frequency stabilization for trapped Yb+ experiments

Thesis (MSc)--Stellenbosch University, 2020.ENGLISH ABSTRACT: This project sets out to frequency stabilize external cavity diode lasers of wavelengths = 935 nm and 739 nm, with an eye to Ytterbium-171 ion trapping. The desired laser linewidths were below 1 MHz at 1 second observation time and the desired long term frequency drifts were below a megahertz over the course of a few hours. To stabilize the lasers, two Pound-Drever-Hall laser frequency stabilisation systems were designed, constructed and characterized. The optical frequency references used were sub-megahertz linewidth optical cavities with Invar spacers. These cavities were designed and constructed inhouse. The achieved long term stability of the stabilized lasers was 1 MHz/h over a 5 hour measurement period. The laser frequency long term stabilities are limited by the thermal stabilities of the cavity spacers. The post stabilisation laser frequency noise was lowered when compared to the free running lasers. This was observed by determining the laser frequency noise power spectral densities. From the frequency noise power spectral densities lower bounds on the locked laser linewidths were established. This lower bound is 11.92 kHz for the 739 nm wavelength laser at 1 second observation time and 5.4 kHz for the 935 nm wavelength laser. An additional system was designed and constructed to stabilize the 935 nm wavelength laser to an in-house built piezo electrically tunable cavity noise power spectral densities to simultaneously stabilize the length of the cavity to a microwave frequency referenced to a Rubidium frequency standard. Technical limitations (optical feedback into the the 935 nm wavelength laser cavity) prohibited the implementation of a stable lock of the cavity length.AFRIKAANSE OPSOMMING: Die doel van die projek is om die frekwensies van diodelasers met eksterne resonansholtes te stabiliseer. Die lasers, met golflengtes = 935 nm en 739 nm, vorm deel van ’n Ytterbium 171 ioonval Die mikpunt was om die laserlynwydte te vernou tot minder as 1 MHz vir ’n sekond lange meeting. Die langtermyn dryf van die laser frekwensies moes ook tot minder as ’n MHz oor ’n paar uur verminder word. Om die lasers te stabiliseer is twee Pound-Drever-Hall laserfrekwensie stabiliseerings sisteme ontwerp, gebou en getoets. Die optiese frekwensie verwysings is twee optiese holtes wat ook ontwerp en gebou is vir hierdie projek. Die langtermyn dryf van die gestibilseerde lasers was 1 MHz/h, soos beperk deur die termiese stabiliteit van die optiese holtes se lengtes. ’n Vermindering in die gestabaliseerde laserslynwydte is waargeneem. Hierdie is bepaal deur die frewkwensie geraas van die lasers te meet. Die gemete laser frekwensie geraas is gebruik om die minimum verwagte laser lynwydtes vas te stel. Hierdie waardes is bepaal as 11.92 kHz vir die 739 nm golflengte laser vir ’n sekonde lange meeting en 5.4 kHz vir die 935 nm golflengte laser. ’n Addisionele optiese holte met verstelbare lengte is ook ontwerp en gebou. Hierdie holte het deel gevorm van ’n sisteem wat die laser met die hulp van ’n optiese holte stabiliseer en tergelyktydig die lengte van die holte met behulp van ’n stabiele mikrogolf frekwensie stabilisieer. Hierdie sisteem is onsuksesvol weens tegniese probleme, naamlik optiese terugvoer in die laser in.The financial assistance of the National Research Foundation (NRF) towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and are not necessarily to be attributed to the NRF.Master

Reassessing evidence of Moon–Earth dynamics from tidal bundles at 3.2 Ga (Moodies Group, Barberton Greenstone Belt, South Africa)

Past orbital parameters of the Moon are difficult to reconstruct from geological records because relevant data sets of tidal strata are scarce or incomplete. The sole Archean data point is from the Moodies Group (ca 3.22 Ga) of the Barberton Greenstone Belt, South Africa. From the time‐series analysis of tidal bundles from a well‐exposed subaqueous sand wave of this unit, Eriksson and Simpson (Geology, 28, 831) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although this study’s detailed geological mapping and section measuring of the site confirmed that the sandstone bed in question is likely a migrating dune, the presence of angular mud clasts, channel‐margin slumps, laterally aggrading channel fills and bidirectional paleocurrents in overlying and underlying beds suggests that this bedform was likely located in a nearshore channel near lower‐intertidal flats and subtidal estuarine bars; it thus carries risk of incomplete preservation. Repeated measurements of foreset thicknesses along the published traverse, measured perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along traverses measured parallel to bedding along the 20.5 m wide exposure are affected by minor faulting, uneven outcrop weathering, changing illumination, weather, observer bias and show a low reproducibility. The most robust measurements herein confirm the periodicity peak of approximately 14 in the original data of Eriksson and Simpson (Geology, 28, 831). Because laminae may have been eroded, the measurements may represent a lower bound of about 28 lunar days per synodic month. This estimate agrees well with Earth–Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a lower orbit around a faster‐spinning Earth.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165