ERC Advanced Grant No. 669666 “INFANT EARTH”

(2015 - 2021)

The Making of the Earth – Reading the Geochemical Code from Meteorites and the Earth’s Oldest Rocks

Figure: Concept and the three principal methodological approaches of INFANT EARTH.

Proposal summary

It is still an open question how Earth became the rocky habitable planet as we know it today. This is because there is a significant time gap of several 100 million years between Earth’s oldest rock archives (ca. 4 billion years old) and most extraterrestrial samples like meteorites that archive the birth of our solar system ca. 4.5 billion years ago. Within this time gap, three key processes that shaped our planet took place, i.e., Earth’s growth via asteroidal collisions, formation of the metal core and a first solid crust, and the delivery of volatiles such as water. Because rock samples are lacking, these fundamental processes have to be traced indirectly, by using highly sophisticated geochemical tools like isotope or trace element compositions of younger rocks or meteorites.
this project aims on better unravelling Earth’s earliest history and better identifying its building blocks, by combining the geochemical record locked in Earth`s oldest rocks and extraterrestrial samples. The key focus of “Infant Earth” is the development of new geochemical techniques that are way beyond the current state of art. The methodology of “Infant Earth” covers three linked approaches, namely high precision analyses of (i) nucleosynthetic isotope anomalies, (ii) radiogenic isotope and (iii) trace element measurements. To better constrain the history of volatile delivery to the nascent Earth, a focus is on comparing the geochemical record provided by refractory and volatile elements. In their synergy, the results will provide a major step forward in unravelling Earth’s earliest history.
INFANT EARTH builds on existing research strengths of the geochemistry/cosmochemistry group at UoC, where a scientifically broad pool of collaborating scientists and state of the art analytical equipment are available. We have also acquired a nearly unique collection of Earth’s oldest rock samples and of extraterrestrial samples supplied from institutions such as NASA or collaborating museums.
 

Fischer-Gödde, M., Elfers, B.M., Münker, C., Szilas, K., Maier, W.D., Messling, N., Morishita, T., Van Kranendonk, M., Smithies, H. (2020): Ru isotope vestige of Earth’s pre-late veneer mantle preserved in Archean rocks. Nature 579: 240-244.
Based on the novel ¹⁰⁰Ru isotope tracer, this study can show that Earth accreted from inner solar system building blocks that are not present in our meteorite collections. The study can also show for the first time that siderophile (i.e., metal loving) elements in Earth’s mantle are not entirely derived from the so called late veneer, the last ca. 0.5 percent of meteorite material that were delivered to Earth after formation of its metal core ceased, thus probing isotope signatures from earth’s early accretion history.
 

Thiemens, M.M., Sprung, P., Fonseca, R.O.C., Leitzke, F.P., Münker, C. (2019): Early Moon formation inferred from hafnium–tungsten systematics. Nature Geoscience 12: 696–700.
This study revises the age of the Moon to ca. 40-60 million years after solar system formation, significantly earlier than previously thought. The revision of the lunar age is based on a more accurate determination of the Hf/W element ratio in the lunar mantle that is the basis for early solar system chronology using the extinct ¹⁸²Hf-¹⁸²W system. The age likely dates core formation on the Moon and it also implies that the Earth-Moon system was more or less formed by ca. 60 million years after solar system formation.
 

Braukmüller, N., Wombacher, F., Hezel, D.C., Escoube, R., Münker, C. (2018): The chemical composition of carbonaceous chondrites: implications for volatile element depletion, complementarity and alteration. Geochimica et Cosmochimica Acta 239: 17-48.
This study presents an unprecedented comprehensive dataset for volatile trace elements in carbonaceous chondrites (i.e., elements with condensation temperatures of less than ca. 800°K in space). In earth sciences these data are important reference parameters in studies that investigate the origin and evolution of planetary bodies in the inner solar system.
 

Braukmüller, N., Wombacher, F., Funk, C., Münker, C. (2019): Earth’s volatile element depletion pattern inherited from a carbonaceous chondrite-like source. Nature Geoscience 12: 564-568.
This study can show for the first time that volatile element in carbonaceous chondrites and on the Earth exhibit a so called “hockeystick pattern”. This means that the abundances of these elements show a first order decrease with decreasing condensation temperatures down to 7500° K, but show constant abundances at condensation temperatures lower than 750°K. Finding this characteristic pattern on Earth can now unambiguously show that the final 10-15 percent of meteoritic material that was delivered to the Earth had a composition similar to CI or CM-like carbonaceous chondrites that originate from the more outer parts of the solar system. The results of this study also allow much improved estimates of volatile element abundances in Earth’s metal core.
 

Münker, C., Fonseca, R.O.C., Schulz, T. (2017): Silicate Earth’s missing niobium may have been sequestered into asteroidal cores. Nature Geoscience 10: 822-826.
This study presents a solution to the so called “Nb-paradox” in geochemistry, i.e., the observation that ca. 20% of the trace element niobium is simply missing in Earth’s silicate mantle. The niobium deficit in Earth’s mantle is likely a vestige of Earth’s early history and was inherited from Earth’s building blocks. It is known that with ongoing growth of the Earth’s, the building blocks were increasingly differentiated bodies (i.e., small asteroids with metal cores and silicate mantles). Upon collision with the Earth, the niobium-rich metal cores merged with Earth’s growing metal core, without fully equilibrating with Earth’s mantle. Conversely, the niobium-poor silicate mantles of the asteroids ended up in Earth’s silicate mantle. The Niobium in Earth’s mantle has therefore been lost to asteroidal cores. Comparing the niobium composition of planetary mantles with composition from asteroids can therefore allow new insight into processes operating during planetary accretion.