The earliest stromatolites were probably formed by
A) anoxygenic phototrophs.
B) anoxygenic lithotrophs.
C) oxygenic phototrophs.
D) oxygenic lithotrophs.

Question

Quizplus · Accepted Answer

The earliest stromatolites were formed around 3.5 billion years ago, during the Archean Eon, by mats of microbes known as cyanobacteria. However, the earliest life forms were likely anoxygenic phototrophs, which used a type of photosynthesis that did not produce oxygen. These microbes were capable of forming primitive stromatolites, which were composed of layers of trapped sediment and microbial mats. Therefore, option A - anoxygenic phototrophs - is the best choice.

The Earliest Stromatolites Were Probably Formed by