<u>Answer:</u>
Approximately, the oldest stromatolites are 3.6 billion years old on earth.
<u>Explanation:</u>
- Stromatolites is not only oldest earths fossil but conspiracy in that they are singular visual portal in deep time on earth. 
- It is defined as laminated accumulation structure that is they stick up above sea floor . 
- Stromatolite buildings includes oldest fossils which are 3.5 billions old when the earth were too unfriendly to support life.
- The study of  fossil age, evolutionary, method of formation are known as paleontology. 
- These specimens are considered as old fossils which are around 3.4 to 4.1 billions years old.
 
        
             
        
        
        
B. they are both unicellular
        
                    
             
        
        
        
I'm gonna go and say it's parenchyma but I'm not 100% sure