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← GeographyWhich process drives the formation of banded iron formations in Precambrian lake deposits?
A)Seasonal cyanobacteria blooms oxidizing dissolved iron✓
B)Tectonic uplift exposing iron-rich sediments rapidly
C)Hydrothermal vent activity precipitating iron sulfides
D)Glacial scouring depositing iron-rich till directly
💡 Explanation
When cyanobacteria photosynthesize, they release oxygen which oxidizes dissolved ferrous iron (Fe2+) in the lakes, causing it to precipitate as insoluble ferric oxide (Fe3+) layers. Therefore, seasonal blooms cause iron formation, rather than uplift, hydrothermal vents, or glacial deposition, which involve different iron sourcing mechanisms.
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