Snowball Earth's iron deposits may have formed through microbes living without sunlight
Iron is one of the most abundant metals on Earth's surface, yet how such massive iron ore deposits formed throughout geological history has long remained a mystery. The prevailing theory has been that ancient photosynthetic bacteria oxidized iron, causing it to precipitate and accumulate in the oceans.
A team of Korean researchers has discovered iron-oxidizing microorganisms and key genes in marine sediments beneath the Antarctic Larsen C Ice Shelf, suggesting that these microbes could have played a role in the formation of massive iron ore deposits, known as banded iron formations (BIFs), during the Cryogenian period of the Neoproterozoic Era.
This era is often referred to as "Snowball Earth," when the planet was covered by ice hundreds of meters thick. The discovery of these microorganisms and their ability to oxidize iron in environments deprived of sunlight and oxygen challenges the previous theory that BIFs were formed through the activity of photosynthetic bacteria.
The researchers found crucial clues in sediment cores collected near the Larsen C Ice Shelf, which preserved records of the marine environment over the past 12,000 years, from the Quaternary Period to the present. The team observed alternating dominance between two distinct microbial groups closely associated with these bacteria, indicating a cyclical pattern that could offer new insights into the formation of ancient iron formations.
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