How did large iron deposits,called banded iron formations,form?
A)hot water circulates along the margins of a caldera
B)groundwater mixes with seawater in the subsurface
C)magma releases metal-rich fluids that replace reactive rocks
D)an increase in oxygen in Earth's atmosphere caused seas to precipitate beds of iron-rich minerals

Question

How did large iron deposits,called banded iron formations,form? 
A)hot water circulates along the margins of a caldera 
B)groundwater mixes with seawater in the subsurface 
C)magma releases metal-rich fluids that replace reactive rocks 
D)an increase in oxygen in Earth's atmosphere caused seas to precipitate beds of iron-rich minerals

Quizplus · Accepted Answer

Banded iron formations are believed to have formed due to an increase in oxygen in Earth's atmosphere, which caused the already existing dissolved iron in the oceans to precipitate and form beds of iron-rich minerals. This process is known as precipitation or sedimentation.

How Did Large Iron Deposits,called Banded Iron Formations,form