Earth's first atmosphere was rich in water vapor but poor in free oxygen.The atmosphere became more oxygenated with the
A)development of the ozone layer.
B)emergence of stromatolites that developed a simple version of photosynthesis.
C)emergence of gases from volcanic eruptions.
D)both A and B.

Question

Quizplus · Accepted Answer

The emergence of stromatolites, which are layered structures formed by cyanobacteria, played a crucial role in oxygenating Earth's atmosphere through photosynthesis, which released oxygen as a byproduct.

Earth's First Atmosphere Was Rich in Water Vapor but Poor