Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact

Abstract

High pressure-temperature experiments suggest late delivery of life-essential elements to Earth by a large differentiated body.

On the Origin(s) and Evolution of Earth's Carbon

“…Recent geochemical datasets show that Earth's volatile elemental ratios (i.e., C/N or C/Si) are nonchondritic, suggesting that elemental fractionation occurred during planetesimal accretion (Hin et al 2017), core formation (Dasgupta et al 2009), giant impact(s), impact-induced atmospheric loss (Bergin et al 2015), or a combination of all these processes (Grewal et al 2019). Thus, long before plate tectonics began cycling and recycling Earth's carbon between the surface and the interior, three recognized periods or events were particularly pivotal in the formation and evolution of the terrestrial carbon reservoirs.…”

“…How much carbon is possibly stored in Earth's core strongly depends on the initial amount of carbon present in the magma ocean, as well on the metal affinity of carbon under core-forming conditions. Over the last decade, experimental studies of the carbon partitioning between Fe-Ni alloy liquid and silicate melt (e.g., Dasgupta et al 2009;Grewal et al 2019) have revealed that the behavior of carbon during metal-silicate equilibration is highly sensitive to the composition of the Fe-rich alloy (including the abundance of the light elements H, N, S, and Si) as well as to the pressure (depth of differentiation), temperature, and oxygen fugacity (Wood et al 2013). Importantly, the debate currently revolves around how much carbon was sequestered into the core, and not if carbon was partitioned into the core (Dasgupta et al 2009;Wood et al 2013;Grewal et al 2019).…”

“…Over the last decade, experimental studies of the carbon partitioning between Fe-Ni alloy liquid and silicate melt (e.g., Dasgupta et al 2009;Grewal et al 2019) have revealed that the behavior of carbon during metal-silicate equilibration is highly sensitive to the composition of the Fe-rich alloy (including the abundance of the light elements H, N, S, and Si) as well as to the pressure (depth of differentiation), temperature, and oxygen fugacity (Wood et al 2013). Importantly, the debate currently revolves around how much carbon was sequestered into the core, and not if carbon was partitioned into the core (Dasgupta et al 2009;Wood et al 2013;Grewal et al 2019). Assuming that a large amount of carbon was accreted to the young Earth and that this was then sequestered to the core, then a significant amount of the carbon now present in the terrestrial mantle must have been delivered to the Earth after core-mantle differentiation, such as by a large impactor and/or during the accretion of the late veneer.…”

“…However, quantifying the effect of the giant impact on carbon geochemistry remains challenging, partly because we do not know the initial or present-day carbon abundance of planet Earth. The Moon-forming impact would have resulted in the melting of most (or all) of Earth's silicate mantle in order to form a silicate vapor disc, this event being followed by the formation of a deep magma ocean (Hin et al 2017;Grewal et al 2019). This stage of Earth's history might have resulted in significant outgassing and the formation of a secondary atmosphere.…”

“…This stage of Earth's history might have resulted in significant outgassing and the formation of a secondary atmosphere. Alternatively, Earth could have gained volatiles from the impactor (Grewal et al 2019). According to the latter scenario, (partial) accretion of a large differentiated body would explain the major volatile element signature of the bulk silicate Earth.…”