Banded-iron formations,such as the one in the image below,show evidence of an
A) oxygen-poor atmosphere because all of the oxygen was dissolved into the oceans and then precipitated as iron-oxide minerals.
B) acidic ocean that forced iron to bond with the oxygen in the water to form iron-oxide minerals.
C) oxygen-poor ocean because all the oxygen was trapped in the iron-oxide minerals that make up the formation.
D) oxygen-rich atmosphere that forced the oceans to become oxidizing and precipitate iron-oxide minerals.

Question

Banded-iron formations,such as the one in the image below,show evidence of an 
A) oxygen-poor atmosphere because all of the oxygen was dissolved into the oceans and then precipitated as iron-oxide minerals. 
B) acidic ocean that forced iron to bond with the oxygen in the water to form iron-oxide minerals. 
C) oxygen-poor ocean because all the oxygen was trapped in the iron-oxide minerals that make up the formation. 
D) oxygen-rich atmosphere that forced the oceans to become oxidizing and precipitate iron-oxide minerals.

Quizplus · Accepted Answer

Banded-iron formations are formed from layers of iron-oxide minerals and silica. They are believed to have formed during the Precambrian era, when the Earth's atmosphere was in the process of becoming oxygen-rich due to the emergence of photosynthetic organisms. As a result of the increasing oxygen levels, the oceans became oxidizing, causing the precipitation of iron-oxide minerals that make up the banded-iron formations. Therefore, the best answer is D, an oxygen-rich atmosphere that forced the oceans to become oxidizing and precipitate iron-oxide minerals.

Banded-Iron Formations,such as the One in the Image Below,show Evidence