About 717 million years ago, Earth experienced a drastic cooling phase, famously known as “snowball Earth.” Ice moved from the poles all the way to the equator, creating a world where the seas were dark and lifeless due to the absence of sunlight. A recent study sheds light on just how cold our oceans were during this time. Researchers reported a sea temperature of about −15°C, possibly the coldest on record.
For ocean water to remain liquid at such low temperatures, it needed to be very salty. This study suggests that some seawater during the Sturtian glaciation— which lasted around 57 million years—could have been four times saltier than today’s oceans. Dr. Ross Mitchell, a geologist, explained that these “salty brines” resemble current conditions in parts of Antarctica, like Lake Vida, which features temperatures dipping to −13°C.
The Sturtian snowball Earth was a consequence of a runaway cooling cycle. Ice reflects sunlight, which cools the planet further, leading to more ice. This cycle could create glaciers up to a kilometer thick, burying much of the Earth under ice.
This extreme period left behind unique geological formations. The iron-rich rocks formed at the boundary where glaciers met ice-covered seas. Researchers have developed a method to use these iron formations as a sort of thermometer, estimating ocean temperatures during snowball Earth.
These iron formations are remnants from an era before Earth’s atmosphere was well oxygenated. The water where the iron collected was rich in iron that transformed from a dissolved state to a solid form, creating the unique “rusty red” rocks. The iron isotopes in these rocks provide clues about the ocean’s temperatures, indicating that they were likely much colder than today’s rates, potentially around 40°C lower. This fascinating usage of iron data offers fresh insights into our planet’s climatic history.
Dr. Andy Heard, a geochemist, highlighted the unique method used in the study for interpreting these ancient rocks. He noted that while the findings suggest seawater was extremely cold, it’s best understood qualitatively, rather than as precise measurements. Similar conclusions were found in other studies analyzing snowball Earth sediments, reinforcing the idea that ocean temperatures plummeted significantly.
Such research not only deepens our understanding of Earth’s past but also raises questions about our current climate trends. It serves as a reminder of the planet’s dynamic history and the natural processes that can lead to significant environmental shifts.
For further reading, you can explore the original article for detailed insights into this ancient climatic event on EOS.org.
