<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Huang, Dongyang</style></author><author><style face="normal" font="default" size="100%">Badro, James</style></author><author><style face="normal" font="default" size="100%">Siebert, Julien</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">The niobium and tantalum concentration in the mantle constrains the composition of Earth's primordial magma ocean</style></title><secondary-title><style face="normal" font="default" size="100%">Proceedings of the National Academy of Sciences</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2020</style></year><pub-dates><date><style  face="normal" font="default" size="100%">nov</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://www.pnas.org/content/early/2020/10/22/2007982117 https://pnas.org/doi/full/10.1073/pnas.2007982117</style></url></web-urls></urls><number><style face="normal" font="default" size="100%">45</style></number><publisher><style face="normal" font="default" size="100%">National Academy of Sciences</style></publisher><volume><style face="normal" font="default" size="100%">117</style></volume><pages><style face="normal" font="default" size="100%">27893–27898</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Silicate Earth is widely considered identical to chondrites in its refractory lithophile element ratios. However, its subchondritic Nb/Ta signature deviates from the chondritic paradigm. To resolve this Nb deficit, its sequestration in Earth&amp;#039;s core under very reducing core-forming conditions has been proposed based on low-pressure data. Here, we show that under conditions relevant to core formation Nb is siderophile at high pressures under all redox conditions, corroborating Nb inventory in Earth&amp;#039;s core. Further core formation modeling shows that Earth&amp;#039;s core could have formed under moderately reducing or oxidizing conditions, whereas highly reducing conditions mismatch the geochemical observables; although Earth may have sampled a variety of reservoirs, it is problematic to accrete primarily from materials as reduced as enstatite chondrites.</style></abstract></record></records></xml>