The presence of which rocks show that between 2 and 3 billion years ago the atmosphere contained less than 1% of the amount of oxygen it contains today?
A) limestone
B) banded iron formations
C) silicate clays
D) sandstone

Question

Quizplus · Accepted Answer

Banded iron formations are sedimentary rocks that formed between 3.8 and 1.8 billion years ago. They contain alternating layers of iron oxides and silicates, indicating that the conditions of the Earth's early atmosphere allowed for the precipitation of iron-rich sediments. The fact that these formations are not present in younger rocks suggests that the buildup of oxygen in the atmosphere initiated the formation of banded iron formations, and that their absence in younger rocks indicates a rise in oxygen levels in the atmosphere to levels above about 1%.

The Presence of Which Rocks Show That Between 2 and 3