24 research outputs found
Hadean geodynamics inferred from time-varying 142Nd/144Nd in the early Earth rock record
Tracking the secular evolution of 142Nd/144Nd anomalies is important towards
understanding the crust-mantle dynamics in the early Earth. Excessive scatter in
the published data, however, precludes identifying the fine structure of
142Nd/144Nd evolution as the expected variability is on the order of few parts per
million. We report ultra-high precision 142Nd/144Nd data for Eoarchean and
Palaeoarchean rocks from the Isua Supracrustal Belt (SW Greenland) that show
a well-resolved 142Nd/144Nd temporal variability suggesting progressive convective
homogenisation of the Hadean Isua depleted mantle. This temporally
decreasing 142Nd/144Nd signal provides a direct measure of early mantle dynamics,
defining a stirring timescale of <250 Myr consistent with vigorous convective
stirring in the early mantle. The 142Nd/144Nd evolution suggests protracted crustal
residence times of ~1000-2000 Myr, inconsistent with modern-style plate tectonics
in the Archean. In contrast, a stagnant-lid regime punctuated by episodes of mantle overturns accounts for the long life-time
estimated here for the Hadean proto-crust
Habitable Zones and UV Habitable Zones around Host Stars
Ultraviolet radiation is a double-edged sword to life. If it is too strong,
the terrestrial biological systems will be damaged. And if it is too weak, the
synthesis of many biochemical compounds can not go along. We try to obtain the
continuous ultraviolet habitable zones, and compare the ultraviolet habitable
zones with the habitable zones of host stars. Using the boundary ultraviolet
radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable
zones of host stars with masses from 0.08 to 4.00 \mo. For the host stars with
effective temperatures lower than 4,600 K, the ultraviolet habitable zones are
closer than the habitable zones. For the host stars with effective temperatures
higher than 7,137 K, the ultraviolet habitable zones are farther than the
habitable zones. For hot subdwarf as a host star, the distance of the
ultraviolet habitable zone is about ten times more than that of the habitable
zone, which is not suitable for life existence.Comment: 5 pages, 3 figure
Gamma-ray irradiation in the early Solar System and the conumdrum of the 176Lu decay constant.
International audienc
Early Earth differentiation investigated through 142 Nd, 182 W, and highly siderophile element abundances in samples from Isua, Greenland
International audienc
Solid-phase Mn speciation in suspended particles along meltwater-influenced fjords of West Greenland
Manganese (Mn) is an essential micro-nutrient that can limit or, along with iron (Fe), co-limit phytoplankton growth in the ocean. Glacier meltwater is thought to be a key source of trace metals to high latitude coastal systems, but little is known about the nature of Mn delivered to glacially-influenced fjords and adjacent coastal waters. In this work, we combine in-situ dissolved Mn (dMn) measurements of surface waters with Mn K-edge X-ray absorption spectroscopy (XAS) data of suspended particles in four fjords of West Greenland. Data were collected from transects of up to 100 km in fjords with different underlying bedrock geology from 64 to 70°N. We found that dMn concentrations generally decreased conservatively with increasing salinity (from 80-120 nM at salinity 25). Dissolved Fe (dFe) trends in these fjords similarly declined with increasing distance from glacier outflows (declining from >20 nM to <8 nM). However, the dMn/dFe ratio increased rapidly likely due to the greater stability of dMn at intermediate salinities (i.e. 10 – 20) compared to rapid precipitation of dFe across the salinity gradient. The XAS data indicated a widespread presence of Mn(II)-rich suspended particles near fjord surfaces, with structures akin to Mn(II)-bearing phyllosilicates. However, a distinct increase in Mn oxidation state with depth and the predominance of birnessite-like Mn(IV) oxides was observed for suspended particles in a fjord with tertiary basalt geology. The similar dMn behaviour in fjords with different suspended particle Mn speciation (i.e., Mn(II)-bearing phyllosilicates and Mn(IV)-rich birnessite) is consistent with the decoupling of dissolved and particulate Mn and suggests that dMn concentrations on the scale of these fjords are controlled primarily by dilution of a freshwater dMn source rather than exchange between dissolved and particle phases. This work provides new insights into the Mn cycle in high latitude coastal waters, where small changes in the relative availabilities of dMn, dFe and macronutrients may affect the identity of the nutrient(s) proximally limiting primary production
Remnants of arc-related Mesoarchaean oceanic crust in the Tartoq Group of SW Greenland
Please help populate SUNScholar with the full text of SU research output. Also - should you need this item urgently, please send us the details and we will try to get hold of the full text as quick possible. E-mail to [email protected]. Thank you.Journal Articles (subsidised)NatuurwetenskappeAardwetenskapp