¹Y.Liu et al. (>10)
Science 377, 1513-1519 Link to Article [DOI: 10.1126/science.abo2756]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
Reprinted with permission of AAAS

The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigated the petrology of olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We found that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multistage cooling of a thick magma body.

^1,2PAUL FROSSARD,¹CLAUDINE ISRAEL,^3,4AUDREY BOUVIER,¹MAUD BOYET
Science 377, 1527-1532 Link to Article [DOI: 10.1126/science.abq735]
¹Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France.
²Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland.
³Bayerisches Geoinstitut, Universität Bayreuth, 95447 Bayreuth, Germany.
⁴Department of Earth Sciences, University of Western Ontario, London, ON N6A 5B7, Canada.
Reprinted with permission from AAAS

The samarium-146 (146Sm)–neodymium-142 (142Nd) short-lived decay system (half-life of 103 million years) is a powerful tracer of the early mantle-crust evolution of planetary bodies. However, an increased 142Nd/144Nd in modern terrestrial rocks relative to chondrite meteorites has been proposed to be caused by nucleosynthetic anomalies, obscuring early Earth’s differentiation history. We use stepwise dissolution of primitive chondrites to quantify nucleosynthetic contributions on the composition of chondrites. After correction for nucleosynthetic anomalies, Earth and the silicate parts of differentiated planetesimals contain resolved excesses of 142Nd relative to chondrites. We conclude that only collisional erosion of primordial crusts can explain such compositions. This process associated with planetary accretion must have produced substantial loss of incompatible elements, including long-term heat-producing elements such as uranium, thorium, and potassium.

¹K.A.Farley et al. (>10)
Science 377, 6614 Link to Article [DOI: 10.1126/science.abo2]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
Reprinted with permisson from AAAS

The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater’s sedimentary delta, finding that the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Magnesium-iron carbonates along grain boundaries indicate reactions with carbon dioxide–rich water under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks have been stored aboard Perseverance for potential return to Earth.