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Study Reveals Iron Deposits Formed in Extremely Cold Brine Pools During Snowball Earth
Confirmed
In Short: The study, published in Nature, reveals that these iron deposits, known as banded iron formations (BIFs), formed in extremely cold brine pools within the ice-covered oceans.
A team of researchers led by Professor Ross Mitchell from the Chinese Academy of Sciences has uncovered how iron deposits formed during Snowball Earth, a period when most of Earth's surface was covered in ice approximately 720 to 635 million years ago.
The study, published in Nature, reveals that these iron deposits, known as banded iron formations (BIFs), formed in extremely cold brine pools within the ice-covered oceans.
These conditions were much harsher than previously thought, with ocean temperatures reaching as low as -15°C (5°F) without freezing, according to geologists and geochemists.
The researchers found that the iron deposits during Snowball Earth had heavier iron particles than those from earlier periods, suggesting a unique environmental perturbation.
Professor Paul Hoffman of Harvard University, one of the original proposers of Snowball Earth, noted that the temperature of the Snowball ocean could explain the anomaly in the iron deposits.
The team's research was sparked when Hoffman wondered if the temperature of the Snowball ocean could account for the unusual iron deposits observed in the rocks.
The study demonstrates that the anomalously high iron isotope values in Snowball iron formations can be attributed to temperature-dependent fractionation in extremely cold brine pools.
These brine pools were colder than those found in Antarctic margins today, representing Earth's coldest recorded ocean temperatures.
The findings help explain the puzzling banded iron formations found at many spots on the planet and shed light on one of Earth’s most mysterious eras.
Dr. Thomas Gernon, a researcher at the University of Southampton, explained that the iron comes from hydrothermal vents on the seafloor, and that the iron-rich layers typically do not accumulate due to atmospheric oxidation.
Professor Mitchell noted that even though Earth's climate system behaved differently during Snowball Earth, Earth's orbital variations continued as usual, contributing to the observed cycles in the rock layers.
The study's results are significant because complex multicellular life is known to have originated during this period of climate crisis, but the mechanisms behind the iron formations were previously unclear.
What this adds
The study adds new insights into the environmental conditions during Snowball Earth and the formation of iron deposits, but it does not fully explain how life survived during this period.
What's confirmed
- A team of researchers led by Professor Ross Mitchell from the Chinese Academy of Sciences has uncovered how iron deposits formed during Snowball Earth, a period when most of Earth's surface was covered in ice approximately 720 to 635 million years ago.
- The study, published in Nature, reveals that these iron deposits, known as banded iron formations (BIFs), formed in extremely cold brine pools within the ice-covered oceans.
- These conditions were much harsher than previously thought, with ocean temperatures reaching as low as -15°C (5°F) without freezing, according to geologists and geochemists.
- The researchers found that the iron deposits during Snowball Earth had heavier iron particles than those from earlier periods, suggesting a unique environmental perturbation.
- Professor Paul Hoffman of Harvard University, one of the original proposers of Snowball Earth, noted that the temperature of the Snowball ocean could explain the anomaly in the iron deposits.
- The team's research was sparked when Hoffman wondered if the temperature of the Snowball ocean could account for the unusual iron deposits observed in the rocks.
- The study demonstrates that the anomalously high iron isotope values in Snowball iron formations can be attributed to temperature-dependent fractionation in extremely cold brine pools.
- These brine pools were colder than those found in Antarctic margins today, representing Earth's coldest recorded ocean temperatures.
- The findings help explain the puzzling banded iron formations found at many spots on the planet and shed light on one of Earth’s most mysterious eras.
- Dr. Thomas Gernon, a researcher at the University of Southampton, explained that the iron comes from hydrothermal vents on the seafloor, and that the iron-rich layers typically do not accumulate due to atmospheric oxidation.
- Professor Mitchell noted that even though Earth's climate system behaved differently during Snowball Earth, Earth's orbital variations continued as usual, contributing to the observed cycles in the rock layers.
- The study's results are significant because complex multicellular life is known to have originated during this period of climate crisis, but the mechanisms behind the iron formations were previously unclear.
What's still developing
- The ice age that the Earth emerged from 12,000 years ago was a mild chill compared to Snowball Earth, the name given to at least two periods where most, if not all, of the planet froze over.
- “No one has found a fatal flaw [in hard Snowball models] but there has been death by a thousand cuts,” as more observations arise that appear to fit the soft snowball better.
- The authors originally assumed they’d measured the era’s global salinity, but Mitchell told IFLScience that after peer review, they acknowledged that, even though the deposits were quite widely distributed, they might represent isolated areas where BIFs could form.
- The team also considered the possibility that the anomaly was caused by heavier iron particles present in the Snowball ocean from glacial erosion on land or hydrothermal vents, but their analysis showed this wasn’t likely.
- About 700 million years ago, Earth was entombed in a veneer of ice hundreds of feet thick—a frozen state scientists refer to as “Snowball Earth.” Oceans cooled but managed to retain some heat to avoid freezing.
- Scientists have been studying how life could have survived the Cryogenian era, which includes the Snowball Earth period, plus another such episode about 650 million years ago.
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- Nature Communications volume 17, Article number: 462 ( 2026 ) Cite this article For the severe low-latitude “snowball Earth” glaciations, glacial deposits occurring on all continents is well-established.
- Importantly, CIF δ 56 Fe values exhibit a wide range of variability only observed in IF deposited prior to the transition to an oxidizing atmosphere during the Great Oxidation Event (GOE) (Fig. 2 ), suggesting an important environmental perturbation.
- According to this framework, the oxidation of Fe 2+ can result in the precipitation of Fe(III) (hydr)oxides that are enriched in isotopically heavy iron, and smaller degrees of partial oxidation (due to lower O 2 availability) along a distillation pathway produce more strongly positive δ 56 Fe values in sedimentary rocks 11, 12.
- In addition to palaeomagnetic support for glacial deposits at low latitudes, snowball Earth is supported by geological evidence including glaciomarine sedimentary features, characteristic “cap carbonates”, and the reprisal of widespread iron formation (IF) deposition since its disappearance in the Palaeoproterozoic Era 1, 2, 3, 4 (Fig.
- These Cryogenian iron formations (CIF) are mineralogically simple (predominantly composed of laminated hematite) and interbedded with glaciomarine deposits 5, 6.