Question

7. Why do scientists think that photosynthetic prokaryotes were probably not the first life forms on Earth?

Answer 1

Microbes were the first inhabitants of Earth. They are single-celled organisms, like bacteria, fungi, and protozoa. Microbes are still found just about everywhere today, thriving in boiling hot thermal springs 
Hope this Helps :D 

Answer 2

Because photosynthesis is  Four stage sequence of how life first developed on Earth way in the being of time small organic molecules