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Determining the Earth’s heterogeneous accretion history and the survival of mantle heterogeneities using Cr isotopes

English title Determining the Earth’s heterogeneous accretion history and the survival of mantle heterogeneities using Cr isotopes
Applicant Schönbächler Maria
Number 169177
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.10.2016 - 30.09.2018
Approved amount 251'730.00
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Keywords (7)

Cr isotopes; heterogeneous accretion; mantle heterogeneity; cosmochemisty; nucleosynthetic anomalies; Archean rocks; formation of the Earth

Lay Summary (German)

Lead
Vor 4.5 Milliarden Jahren bildete sich die Erde durch die Kollision von kleineren planetaren Körpern und Trümmerteilen, wie wir sie auch heute noch im Asteroidengürtel finden können. Der letzte grosse Wachstumsschritt der Erde war eine riesige Kollision der frühen Erde mit einem Körper von der Grösse des Mars, welche zur Entstehung des Mondes führte. Es ist von fundamentaler Bedeutung, die frühe Wachstumsgeschichte der Erde und die chemische Zusammensetzung der Bausteine der Erde zu kennen, um verstehen zu können, wie ein bewohnbarer Planet entstehen kann und wie wir nach bewohnbaren Exoplaneten ausserhalb unseres Sonnensystem suchen können.
Lay summary

Das Ziel dieses Projektes ist zu ermitteln, ob Teile vom Erdmantel die zur Mondbildung führende gigantische Kollision unbeschadet überlebt haben und uns bis heute erhalten blieben. Dies würde eine wertvolle Tür öffnen, die uns erlaubt, die früheste Kindheit der Erde zu untersuchen.

Um dieses Ziel zu erreichen, werden wir neue analytische Techniken entwickeln für hochpräzise Chromisotopenanalysen. Mit diesen Analysetechniken werden ausgewählte archaische Gesteine untersucht, die zu den ältesten Gesteinen der Erde gehören. Das Ziel ist, Unterschiede zu identifizieren, die von unterschiedlichem Baumaterial der Erde herrühren.

Dieses Projekt erlaubt ein vertieftes Verständnis über den Zeitpunkt an dem flüchtige Elemente auf die Erde gekommen sind. Es wird unser Wissen über die wichtigen chemischen und physikalischen Prozesse erweitern, die während der Bildung der Erde und der nachfolgenden Entwicklung von Mantel und Kruste vorherrschten.

Direct link to Lay Summary Last update: 10.11.2016

Lay Summary (English)

Lead
The Earth’s birth was initiated about 4.5 billion years ago through collisions with small planetary bodies and debris. The last big addition of material likely involved a giant collision of the growing Earth with a Mars-sized body, which led to the formation of our Moon. Constraining the early formation history of the Earth and the chemical composition of its building blocks is vital to understand how to build a habitable planet and how to search for habitable exoplanets outside our solar system.
Lay summary

The goal of this project is to determine whether part of the Earth’s mantle survived the moon-forming giant impact unharmed and was preserved until today. This would provide a powerful window back to study the earliest history of infant Earth.

To this end, we will develop new analytical techniques to obtain ultra high-precision Cr isotope analyses. We will apply these techniques to selected Archean rocks, which are among the oldest known rocks on Earth, and present day mantle samples to determine potential variations that originate from different building material of the Earth.

This work will improve our understanding of when volatile elements were delivered to the Earth as well as the physical and chemical processes at work during the Earth’s growth and subsequent evolution of crust and mantle.

Direct link to Lay Summary Last update: 10.11.2016

Responsible applicant and co-applicants

Employees

Publications

Publication
The Stubenberg meteorite-An LL6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field
Bischoff Addi, Barrat Jean-Alix, Bauer Kerstin, Burkhardt Christoph, Busemann Henner, Ebert Samuel, Gonsior Michael, Hakenmüller Janina, Haloda Jakub, Harries Dennis, Heinlein Dieter, Hiesinger Harald, Hochleitner Rupert, Hoffmann Viktor, Kaliwoda Melanie, Laubenstein Matthias, Maden Colin, Meier Matthias M. M., Morlok Andreas, Pack Andreas, Ruf Alexander, Schmitt-Kopplin Philippe, Schönbächler Maria, Steele Robert C. J., et al. (2017), The Stubenberg meteorite-An LL6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field, in Meteoritics & Planetary Science, 52(8), 1683-1703.

Collaboration

Group / person Country
Types of collaboration
Durham University Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
81st Annual Meeting of The Meteoritical Society 2018 (LPI Contrib. No. 2067) Talk given at a conference GENETIC RELATIONSHIPS OF SOLAR SYSTEM BODIES BASED ON THEIR NUCLEOSYNTHETIC TITANIUM ISOTOPE COMPOSITIONS 22.07.2018 Moskau, Russia Schönbächler Maria;
Goldschmidt 2017, France, Paris, 13.08.2017 Talk given at a conference Tracing volatile accretion to Earth using Cr isotopes 13.08.2017 Paris, France Schönbächler Maria; Steele Robert;


Knowledge transfer events

Active participation

Title Type of contribution Date Place Persons involved
Geotreff für Geographie Lehrer Talk 08.05.2018 Zürich, Switzerland Schönbächler Maria;


Communication with the public

Communication Title Media Place Year
Talks/events/exhibitions Expedition Sonnensystem International German-speaking Switzerland 2018
Talks/events/exhibitions focus Terra - Expedition Sonnensystem International German-speaking Switzerland 2018

Associated projects

Number Title Start Funding scheme
179129 Tracking planet formation, differentiation and the moon-forming giant impact: an integrated approach using non-traditional stable isotopes 01.04.2018 Project funding (Div. I-III)

Abstract

The Earth accreted about 4.5 billion years ago through collisions with planetesimals, planetary embryos and chondritic debris in the solar system. The Earth’s accretion is an important event for the subsequent evolution of our planet, but also for general discussions related to planet formation, for example, in the context of exoplanet research. It has been proposed that the Earth was built from volatile-depleted precursors and that subsequently, volatiles were added during a late veneer after core formation ceased (e.g., Albarède, 2009; Ballhaus et al., 2013). This idea has been challenged and a substantial body of work indicates that volatile-rich, oxidised material was already added during the later stages of the Earth’s accretion, while core formation was still ongoing (O'Brien et al., 2006; Rubie et al., 2011; Rubie et al., 2015; Schönbächler et al., 2010; Wood et al., 2008). In addition, during this later time, a giant impactor struck the proto-Earth and this collision ended in the formation of the Earth’s Moon. This last big accretion step was followed by the late veneer (accretion of < 1 % of the Earth’s current mass (e.g., Walker, 2009).A growing amount of evidence suggests that mantle heterogeneities have survived since the accretion of the Earth (Mukhopadhyay, 2012; Touboul et al., 2012). Willbold et al. (2011) analysed some of the Earth’s oldest rocks from the Archean Isua greenstone belt (Greenland). Based on evidence from the short-lived 182Hf-182W decay system and the preservation of positive 182W variations in Isua rocks, these authors proposed that Isua rocks preserved a signal from the Earth’s mantle that was established before the late veneer. Two other studies (Mukhopadhyay, 2012; Touboul et al., 2012) offer the even more exciting possibility that some mantle heterogeneities may predate the giant impact. In this case, the W isotope signature of Isua rocks may reflect that of the Earth’s mantle from before the moon-forming giant impact and this would allow for unique insights into the early time of the Earth’s accretion.Here we aim to test the preservation of pre-giant impact mantle based on the heterogeneous accretion model of Schönbächler et al. (2010). This model uses various radioactive decay systems to determine the accretion history of the Earth. Since parent and daughter elements of the considered decay systems are differently affected by volatility-related processes, they can track the timing of volatile addition to the Earth. In the framework of Schönbächler et al.’s work, a late volatile addition coincides with the time window of the giant impact. A consequence of volatile addition during, or before, the giant impact, is the sudden enrichment of the bulk mantle in 53Cr from the decay of 53Mn (volatile-rich materials possess high Mn/Cr ratios, thus experience considerable 53Cr ingrowth from 53Mn decay). The volatile-depleted mantle has a lower 53Cr content and admixing of volatile-rich material - in the correct mass fraction required to reconcile the evidence from the different decay systems - will produce a small, but measurable effect in the 53Cr/52Cr ratio of 7 ppm. Additional 53Cr isotope variations may be generated, if global silicate differentiation was well underway within the first 20 million years of our solar system, which is considered unlikely by many studies (e.g., Caro et al., 2008).In this proposal, we aim to determine potential differences between the Isua mantle source and the present day mantle to test (i) whether the Isua source records the mantle composition from before the giant impact, (ii) the origin and the volatile element content of Theia (the moon-forming impactor), and (iii) the possibility of early silicate differentiation on the Earth within less than 20 Myr after the start of the solar system. This will be achieved by the careful set-up of ultra high-precision Cr isotope analyses using TIMS and MC-ICPMS and the application of these analyses to selected Archean rocks and present day mantle samples.
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