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Summary The advent of embryophytes (land plants) is among the most important evolutionary breakthroughs in Earth history. It irreversibly changed climates and biogeochemical processes on a global scale; it allowed all eukaryotic terrestrial life to evolve and to invade nearly all continental environments. Before this work, the earliest unequivocal embryophyte traces were late Darriwilian (late Middle Ordovician; c. 463–461 million yr ago (Ma)) cryptospores from Saudi Arabia and from the Czech Republic (western Gondwana). Here, we processed Dapingian (early Middle Ordovician, c. 473–471 Ma) palynological samples from Argentina (eastern Gondwana). We discovered a diverse cryptospore assemblage, including naked and envelope‐enclosed monads and tetrads, representing five genera. Our discovery reinforces the earlier suggestion that embryophytes first evolved in Gondwana. It indicates that the terrestrialization of plants might have begun in the eastern part of Gondwana. The diversity of the Dapingian assemblage implies an earlier, Early Ordovician or even Cambrian, origin of embryophytes. Dapingian to Aeronian (Early Silurian) cryptospore assemblages are similar, suggesting that the rate of embryophyte evolution was extremely slow during the first c. 35–45 million yr of their diversification. The Argentinean cryptospores predate other cryptospore occurrences by c. 8–12 million yr, and are currently the earliest evidence of plants on land.

The Argentine Precordillera is a continental fragment rifted from the Ouachita embayment of the southern margin of Laurentia (North America) during Cambrian time [about 515 million years ago (Ma)] and accreted to the western margin of Gondwana (South America) during Ordovician time (about 455 Ma). Similarities of Cambrian stratigraphic successions and faunas, Grenville basement rocks, and dimensions link the Argentine Precordillera to the Ouachita embayment. Evidence of rifting during Cambrian time and of a wide ocean basin during Ordovician time indicates that the Precordillera traveled as an independent microcontinent to collide with Gondwana.

Microbialites comprise the mineralized record of early life on Earth and preserve a spectrum of fabrics that reflect complex physical, chemical, and biological interactions. The relatively rarity of microbialites in modern environments, however, challenges our interpretation of ancient structures. Here we report the occurrence of microbial mats, mineral precipitates, and oncoids in the Laguna Negra, a high-altitude hypersaline Andean lake in Catamarca Province, Argentina. Laguna Negra is a Ca-Na-Cl brine where abundant carbonate precipitation takes place. Extreme environmental conditions, including high UV radiation, elevated salinity, and temperature extremes, restrict multicellular life so that mineralization reflects a combination of local hydrologic conditions, lake geochemistry, and microbial activity. The resulting carbonates consist of micritic laminae, botryoidal cement fans, and isopachous cement laminae that are strikingly similar to those observed in Proterozoic stromatolites, providing insight into mechanisms of mineralization. Here, increased saturation with respect to carbonate minerals reflects mixing of spring-fed inlets and lake waters, favoring microbialite formation and preservation. This highlights the importance of hydrological mixing zones in microbialite formation and as taphonomic windows to record microbial activity. Recent discoveries of minerals related to evaporating playa-lake systems on Mars further highlights the potential of Laguna Negra to provide critical insight into biosignature preservation in both terrestrial and extraterrestrial settings.

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The Famatina belt, southern central Andes, records a circa 470 m.y. shortening episode (Ocloyic orogeny) affecting the peri‐Gondwanan back arc basin in response to the accretion of the Precordillera terrane. Collision created distinct features across and along the margin, some of which persisted into the present Andean structure. From east to west, the Ocloyic deformation is recorded across the telescoped region of Famatina, represented by (1) an east vergent fold‐thrust belt (EVFTB) involving a major angular unconformity between Early and Middle Ordovician rocks, (2) a highly deformed volcano‐sedimentary belt, and (3) an east vergent ductile shear zone affecting Famatinian granites. Axis attitudes of Ordovician refolded anticlines in the EVFTB show west‐east tectonic transport, in agreement with kinematics of Ocloyic high‐strain belts, indicating shortening orthogonal to the present Pacific margin. Eastward displacement of the Ordovician volcanic arc at ∼27°S latitude together with a documented sinistral slip zone across the proto‐Andean margin suggests tectonic indentation.

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