Periodic Reporting for period 1 - Complementarity (A unifying model: bulk chondrite complementarity by individual chondrule-matrix mentality)
Período documentado: 2018-08-01 hasta 2020-07-31
The key building blocks of the rocky planets in our Solar System may be represented by chondrules, once molten silicate spherules that are the main constituents of chondritic meteorites. These in turn are fragments of asteroids, planetary bodies that did not make it into becoming planets. When studying these chondritic fragments, we are probing the very first solids that agglomerated in the Solar System and with that, the initial conditions that are key to Earth’s habitability. Chondrites mainly consist of volatile-depleted chondrules and volatile-rich matrix, which contains water and organics. Potential genetic links between the chondrules and matrix can provide important clues into how actively these components were transported throughout our Solar System before finally being accreted into planets and asteroids. For example, did Earth acquire a matrix-component only from the relatively dry inner Solar System or could this component have arrived from the wet outer Solar System, from regions were comets and icy planets accreted? Answering this question is critical to understand how and when prebiotic molecules arrived on Earth. Hence, the main objective of this project was to investigate the genetic links, or potential complementarity, between chondrules and matrix by probing their chemical and isotopic make-up. The current state of the art is undecided whether complementarity exists or not.
1) The first step towards this goal was identifying and obtaining appropriate meteorite samples, which included chondrites that experienced the least amount of secondary alteration. This alteration could be, for example, terrestrial weathering, during which chemical exchange between chondrules and matrix could overprint the original signatures.
2) The selected meteorites were prepared for detailed petrological characterization and chemical analyses of individual chondrules and surrounding matrix areas, to provide insights into potential complementary relationships between these components.
3) This hypothesis was further tested by Cr and Zn isotope analyses of chondrules and matrix, which can elucidate the heritage of materials from which these components are formed and the physical processes behind chondrule formation.
4) A start has been made to date the chondrules using the Pb-Pb dating system and, thereby, combining all results, provide a spatiotemporal model of chondrule storage and transport dynamics to trace the evolution of planetary building blocks.
5) The final step was to disseminate these results into publications, at conference and seminar meetings and to formulate new ideas from these results into grant proposals.
The main scientific goal of this project was to address the issue of chondrule-matrix complementarity in chondrites. By approaching this issue from several angles, namely chemically and isotopically, using multiple isotope systems, it was possible to resolve that this proposed complementarity does not exist. In detail, the chemical and isotopic composition of different stages of chondrule formation and the primitive volatile-rich dust that surrounds these chondrules do not reflect a common genetic origin. This implies that they formed separate from each other and were transported together to their final accretion region onto their parent asteroids. This has fundamental implications for how we think planets formed and what types of materials they accreted. For Earth in particular, the results from this project indicate that our planets’ volatile inventory (e.g. water and organics) were delivered early in the first million years of Solar System formation. In contrast, the current paradigm favors a volatile delivery model in which comets or water-rich asteroids from the outer Solar System delivered water at some point in Earth’s history. Instead, the project results suggest that the delivery of volatiles occurred through chondrule accretion (e.g. the pebble accretion model), which progressively carried volatile-rich dust rims into Earth’s feeding zone.
References:
+ Van Kooten EMME, Cavalcante L, Wielandt D, Bizzarro M (2020) MAPS 55, 575-590.
+ Van Kooten EMME, Moynier F (2019) GCA 261, 248-268.
+ Van Kooten EMME, Moynier F, Agranier A (2019) PNAS 116, 18860-18866.
+ Van Kooten EMME (2019) Zenit, January 2019.
+ Day J, van Kooten EMME, Moynier F (2019) EPSL 531, 115998.