From the origin of Earth's volatiles to atmospheric oxygenation

Project Information

O2RIGIN

Grant agreement ID: 636808

DOI

10.3030/636808

Project closed

EC signature date 23 February 2015

Start date 1 March 2015

End date 31 August 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 498 353,00

EU contribution

€ 1 498 353,00

Coordinated by

EBERHARD KARLS UNIVERSITAET TUEBINGEN
Germany

Periodic Reporting for period 4 - O2RIGIN (From the origin of Earth's volatiles to atmospheric oxygenation)

Reporting period: 2019-09-01 to 2021-08-31

Summary of the context and overall objectives of the project

Aim of this project is to understand the connection between endogenic and exogenic processes of our planet that led to the redox contrast between Earth’s surface and interior. For this purpose the time constraints on atmospheric oxygenation can be refined and for the first time linked with a new approach to Earth’s endogenic processes like plate tectonics, mantle melting, volcanism, continent formation and subduction-related sediment- and crust recycling. These objectives will be achieved by using the unique geochemical capabilities of various stable isotope systems including the Selenium (Se) isotope system to unlock the geological record of changing oxygen fugacities in the mantle-crust-atmosphere reservoirs. The power of the Se isotope system lies in its redox sensitivity and in the volatile and highly siderophile/chalcophile character of elemental Se. This links Se to the evolution of other volatiles during key geological processes from Earth formation ca. 4.5 Ga ago until today. The occurrence and behavior of Se is fully controlled by accessory micrometric sulfide minerals in the silicate Earth, which may conserve their original Se isotopic signatures over large geological timescales and can be linked to a minimum age via Os isotopes. This offers high resolutions in time and space that are groundbreaking for research on Earth System Oxygenation. Covering Earth geologic history, new high-precision Se isotope data of the sedimentary and representative mantle-derived magmatic rock record from all major plate tectonic settings will be combined with the mineral-scale record of robust and global sulfide inclusions in deep mantle minerals. Once the evolution into todays dynamic Earth’s Redox System is understood, the investigation will be pushed back in time to Earth’s formation. This involves a reconciliation of the meteoritic and Archean rock and mineral-scale Se isotope record to constrain the origin of volatiles essential for the oceans, generation of an atmosphere and development of life on our planet.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Following recruitment of team members and training of each individual team member for their respective tasks, a new analytical method was developed that could be used to reach the objectives.
During this developing period the basis for the entire project was successfully established. This includes the development and setup of routine Se isotope and elemental Se-Te analyses of various geological materials (Kurrawa et al. 2017; Yierpan et al., 2018). This method now available at the host institution is the most precise and to date, worldwide only one that is applicable to small amounts of rock samples and Earth's interior-related research.
In a second step the various terrestrial (Kurzawa et al 2018; Yierpan et al. 2019) and extraterrestrial reservoirs (Labidi et al., 2018) were characterised in terms of their elemental and isotopic signatures. Among the first results are coupled Se isotope and Se-Te elemental data of mid ocean ridge basalts, mantle peridotites, ocean island and subduction zone basalts, that altogether contribute to the ongoing characterisation of various terrestrial reservoirs.
In a third step the different results were taken together to investigate processes that established signatures or created exchange between Earth's reservoirs. in combination with continuously generated new literature first models emerged about possible scenarios that could be exceptionally well traced with our methodology. For instance the origin of volatiles on Earth and the cycling of volatiles through the Earth's interior by plate tectonic and mantle convective processes.
In a fourth step the first groundbreaking scientific papers of the project were prepared, submitted and successfully steered through the peer-review process until publication.
To date several groundbreaking publications directly address the main objectives of the O2RIGIN project: Varas-Reus et al. (2020) published in Nature Geoscience shows that Selenium isotopes are tracers of a late volatile contribution to Earth from the outer Solar System. Yierpan et al. (2020) published in Science Advances shows that recycled selenium in hot spot–influenced lavas records ocean-atmosphere oxygenation.
The fifth step is to take the aquired skills of high-precision Se isotope measurements and the knowledge about what these signatures mean on to investigate inclusions in deep mantle minerals. For this first individual sulphide samples were analysed for combined S-Se isotopes (König et al., 2019), combinations with Re-Os isotope dating methods tested and deep mantle sample materials acquired that are now being investigated.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The chemical separation (Yierpan et al., 2018) and instrumental measurement techniques (Kurrawa et al., 2017) established in this project allow for unprecedented precision of Se isotope and Se-Te elemental analysis of geological materials such as mafic rocks (Yierpan et al., 2019), chondritic meteorites (Labidi et al., 2018) and single sulfides (König et al., 2019) with as low as 3 ng total Se.
In contrast to all previously published studies, our technique allows for the first time to resolve Se isotope variations between different chondritic meteorites (Labidi et al., 2018), with cosmochemical implications for the understanding of sulfide formation in the early solar nebula and potential for discriminating between meteorites as building materials for Earth and the origin of terrestrial volatiles.
Origin of Earth's volatile elements from the Outer Solar System could be constrained for the first time from the perspective of stable isotopes of a highly siderophile and volatile element (Varas-Reus et al. (2020, Nature Geoscience).

High-precision isotope measurements of the volatile element selenium in hot spot volcanic rocks showed that ancient surface oxidation signatures were transferred into the deep mantle by subduction where they survived for billions of years. Within the framework of most recent models based on Se systematics, the results further imply that our atmosphere ~1–2 billion years ago probably contained much more oxygen than widely assumed in the scientific community. In addition, these newly constrained selenium isotope systematics highlight how exactly volatile elements in the Earth’s atmosphere, continents and mantle are linked by a large geological cycle (Yierpan et al., 2020, Science Advances). Moreover, selenium isotopes show the highly oxidized nature of slab fluids in modern subduction zone systems (König et al., 2021, Geochemical Perspectives Letters).

Together with the possibility to analyse Os isotopes of the same dissolved sample material, it is expected that, for the first time, robust Os isotope minimum ages can be obtained for a given Se isotope signature. This will push the limits in exploring the terrestrial volatile and redox evolution from the perspectives of single and deep mantle sulfides through Earth's geological history. Another significant finding is that selenium isotopes may contribute to trace the existence of deep microbial life (Cabral et al., 2021, Geology).

Earth's interior-exterior interaction