Scientists Pinpoint Earth's Coldest Oceans During Ancient Deep Freeze

(MENAFN- The Arabian Post) Scientists have identified what may be the coldest ocean temperatures ever recorded in Earth's history, shedding new light on how life endured a planet-wide freeze roughly 700 million years ago. The findings, drawn from advanced chemical analyses of ancient marine sediments, suggest that global oceans during the Cryogenian period cooled to levels close to, and in some regions possibly below, the freezing point of seawater, while remaining partially liquid beneath thick ice cover.

The research focuses on the so-called Snowball Earth episodes, when ice sheets extended from the poles to near the equator and oceans were sealed beneath ice hundreds of metres thick. Until now, scientists believed that even during these extreme glaciations, ocean waters retained enough heat to remain several degrees above freezing. The latest work challenges that assumption by indicating far colder marine conditions than previously estimated.

Using refined isotope techniques applied to carbonate rocks formed on the seafloor, researchers reconstructed seawater temperatures with higher precision than earlier methods allowed. These chemical signatures act as time capsules, preserving information about the temperature and composition of ancient oceans. Results indicate sustained near-freezing conditions across large swathes of the global ocean, making this period the most severe marine cold spell known.

The implications extend beyond climate history. Life on Earth at the time consisted largely of simple, single-celled organisms, yet these communities survived despite what would appear to be hostile, energy-starved conditions. Scientists say the persistence of life suggests the existence of ecological refuges beneath the ice, where limited light and chemical energy sources supported microbial ecosystems.

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Geological evidence points to cracks, thin ice zones and areas of open water, possibly near volcanic regions, that could have allowed sunlight to penetrate and drive photosynthesis. At the same time, hydrothermal vents on the ocean floor may have provided heat and nutrients, creating pockets where organisms could endure prolonged global cold.

The study also refines the timeline of Cryogenian glaciations, which occurred between about 720 million and 635 million years ago. Two major ice ages during this interval appear to have differed in intensity, with the later phase showing the coldest ocean conditions. This aligns with sediment records indicating reduced biological activity and slower chemical weathering on land, consistent with a planet locked in ice.

Climate scientists say the findings help clarify how Earth's climate system operates at its extremes. A fully ice-covered planet reflects far more sunlight back into space, reinforcing cold conditions. The persistence of liquid oceans beneath ice demonstrates how geothermal heat and ocean circulation can prevent complete freezing, even under severe surface conditions.

The work also informs the search for life beyond Earth. Planets and moons with icy surfaces and subsurface oceans, such as those in the outer solar system, are considered potential habitats for life. Understanding how organisms survived Earth's coldest oceans offers clues to how life might persist in similar environments elsewhere.

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