Question

During the late Neoproterozoic Era, roughly 635 million years ago, Earth experienced the Marinoan glaciation, culminating in the rapid deposition of thick sedimentary cap carbonates directly atop glacial debris. Geoscientists have long debated whether this event was a "hard Snowball Earth"—characterized by complete global freeze-over and severed oceanic-atmospheric exchange—or a "slushball" scenario with persistent equatorial open waters and active hydrological cycling.

Recent geochemical investigations have focused on mass-independent triple-oxygen isotope anomalies ($\Delta^{17}\text{O}$) preserved in sedimentary barite deposits embedded within basal cap dolostones. Atmospheric oxygen and carbon dioxide undergo photochemical reactions that impart an anomalous $\Delta^{17}\text{O}$ signature to atmospheric $\text{CO}_2$, an anomaly that is rapidly diluted and erased under normal conditions by the oxygen flux generated from active terrestrial and oceanic biospheric photosynthesis. The basal barite layers exhibit profound negative $\Delta^{17}\text{O}$ anomalies, signifying that they crystallized in waters equilibrated with an atmosphere bearing exceptionally high carbon dioxide concentrations alongside severely depressed photosynthetic activity. Because sustained open-water equatorial refugia would have supported sufficient biological primary productivity to equilibrate atmospheric oxygen isotopes via steady photosynthetic turnover, the persistence and magnitude of these isotopic anomalies indicate that biological carbon fixation was largely suppressed for prolonged intervals, aligning tightly with the extreme ice-cover dynamics predicted by the hard Snowball hypothesis.

Based on the passage, which of the following statements about late Neoproterozoic atmospheric and geochemical conditions are logically supported? (Select all that apply.)