Briny oceans stayed liquid at -15°C during Snowball Earth
During Earth's Snowball Earth period, iron-oxide records indicate subglacial seawater cooled to about -15°C, kept liquid by hypersaline brines up to four times saltier than modern oceans. Researchers used iron isotopes as a thermometer to estimate both temperature and salinity of ancient sea pockets formed during the Sturtian glaciation, suggesting an extraordinary cold but still-liquid briny ocean beneath global ice.