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While molecular clock studies suggest a Tonian-Cryogenian (~800–635 Ma) emergence of the Porifera, convincing fossil evidence of sponges is seen only as far back as ~530 Ma. The >100 Ma lacuna for sponges represents a critical missing piece of the Neoproterozoic puzzle. Assembling an evolutionary framework requires that Poriferan antiquity be understood in terms of sponge form and function, and the emergence of suspension-feeding amid profound environmental and climatic change. Here we report newly discovered biomineralized fossils of sponge-grade animals in Neoproterozoic carbonates of Siberia, Australia, and Brazil. Using a wide range of petrographic, eProbe, µXRF, µCT, and serial grinding techniques, the sponge-grade fossils are shown to be remarkably preserved in three dimensions, displaying broad morphological characters associated with early experiments in biomineralization such as siliceous spicules and external carbonate shells. Reconstructions of their bauplan reveal forms evolutionarily equipped for a suspensionfeeding lifestyle, well-prepared for pumping seawater through their bodies. As ecosystem engineers that clarified the water column and allowed for greater depths of photosynthetic activity, the emergence (and dominance) of sponge-grade animals in shallow marine carbonate reefs had the potential to drive environmental change that is arguably recorded during extremes in the Neoproterozoic carbon cycle. With their global distribution, these animals would link the planktic and benthic realms for the first time in Earth history and represent a sink for the photosynthetically derived organic matter that impacted the oxidation state of the oceans and atmosphere. Notably, most of these fossils are archived in carbonates preserving global expressions of profoundly negative δ13C perturbations. These include the Ediacaran Period Shuram Excursion, which foreshadowed the widespread appearance of the Ediacara biota, and the terminal Cryogenian Period Trezona Anomaly, which immediately preceded the Marinoan snowball Earth. 

Carbonate mud represents one of the most important geochemical archives for reconstructing ancient climatic, environmental, and evolutionary change from the rock record. Mud also represents a major sink in the global carbon cycle. Yet, there remains no consensus about how and where carbonate mud is formed. Here, we present stable isotope and trace-element data from carbonate constituents in the Bahamas, including ooids, corals, foraminifera, and algae. We use geochemical fingerprinting to demonstrate that carbonate mud cannot be sourced from the abrasion and mixture of any combination of these macroscopic grains. Instead, an inverse Bayesian mixing model requires the presence of an additional aragonite source. We posit that this source represents a direct seawater precipitate. We use geological and geochemical data to show that “whitings” are unlikely to be the dominant source of this precipitate and, instead, present a model for mud precipitation on the bank margins that can explain the geographical distribution, clumped-isotope thermometry, and stable isotope signature of carbonate mud. Next, we address the enigma of why mud and ooids are so abundant in the Bahamas, yet so rare in the rest of the world: Mediterranean outflow feeds the Bahamas with the most alkaline waters in the modern ocean (>99.7th-percentile). Such high alkalinity appears to be a prerequisite for the nonskeletal carbonate factory because, when Mediterranean outflow was reduced in the Miocene, Bahamian carbonate export ceased for 3-million-years. Finally, we show how shutting off and turning on the shallow carbonate factory can send ripples through the global climate system. 

The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown.