From Rocks Formed at the Time of the Archean-Proterozoic Transition

From rocks formed at the time of the Archean-Proterozoic transition (2.5 billion years ago) , there is evidence

A) that an abrupt change in the nature of life on Earth had occurred.
B) of a decline in the offshore, cone-shaped cyanobacterial mounds.
C) of an abrupt increase in the growth of stromatolites produced by cyanobacteria.
D) that eukaryotic algae existed, but cyanobacteria remained more abundant.