Cyanobacteria Fossils can be dated back to the ______ , while fossils of ichyosaurs indicate that they lived..?

The answer is D, though the Precambrian, the time when primitive life like Cyanobacteria evolved, is not actually considered an "era". The Mesozoic era was the time when the Dinosaurs roamed the Earth, and Ichthyosaurs were a type of Dolphin-like Reptile that lived in the ocean at that time.