A study published in
Science Advances demonstrates, through experiments conducted at very high pressure and high temperature at the Institute of Earth Physics of Paris (IPGP), that volatile elements—key elements for habitability—were incorporated earlier than previously thought, from the very first stages of Earth's formation.
These results challenge the dominant scenario which posited that these elements were mostly added later by a "late veneer" of volatile-rich meteorites.
Formation of Earth / @IPGP. The late veneer theory called into question
For over fifty years, the so-called "late veneer" model has occupied a central place in theories of Earth's formation. According to this hypothesis, during the planet's initial differentiation—when the metallic core separated from the mantle—elements with an affinity for iron would have been almost entirely drawn towards the center. The mantle would therefore have been strongly depleted in volatile elements like sulfur (S), selenium (Se), and tellurium (Te).
To explain their current abundances, a subsequent contribution of extraterrestrial material, particularly carbonaceous meteorites, would have been necessary to enrich the Earth after its core formed. These new experiments show that this scenario must be profoundly reevaluated.
Reproducing the extreme conditions of primitive Earth
To directly test this hypothesis, researchers reproduced in the laboratory the extreme conditions prevailing during Earth's core formation, comparable to those of a deep magma ocean.
The experiments were conducted at IPGP using a laser-heated diamond anvil cell. Nanoscale analyses of element distribution between metal and silicate were carried out at the European Synchrotron Radiation Facility (ESRF) in Grenoble.
These results are now based on measurements taken under conditions truly relevant for core formation, rather than on probabilistic estimates derived from lower-pressure and lower-temperature experiments that previously supported the hypothesis of a massive late veneer.
A volatile-rich Earth from its growth
The results show that, under these realistic core-formation conditions, sulfur, selenium, and tellurium are less strongly attracted to the core than indicated by experiments conducted at lower pressure. In other words, the Earth's mantle could have retained a significant fraction of these elements from the planet's initial differentiation.
Models based on this new data indicate that the late veneer—if it existed—would have been limited to about 0.1% of Earth's mass, or four to five times less than classic estimates.
These results therefore suggest that Earth's budget of volatile elements—and potentially a significant portion of its water—was established mainly during the initial accretion phase, during the very growth of the planet, and not during a major late episode.
Implications for the origin of habitability
This revision of Earth's accretion scenario profoundly alters our understanding of the origin of elements essential for life. If volatiles were incorporated gradually from the first stages of planetary formation, it means that a planet's habitability could depend more on its early accretion history than on an exceptional late event.
The results thus open new perspectives on the formation of terrestrial planets and the distribution of volatile elements in the Solar System.