Stromatolites are rocky structures that generally form in shallow waters from the binding of sediment by microbial biofilms. Stromatolites are typically hypothesized to be formed from the presence of cells that bind these grains together. If the appearance of the stromatolites in the fossil record were to indicate the emergence of life on earth, approximately how old are the oldest stromatolites on earth? A) 2.6 billion years old B) 3.6 billion years old C) 4.6 billion years old D) 400 million years old