In this passage author is introducing two kinds of theories about how living is forming.One is that people believe living needs energy from photosynthesis.The other believes living can use just energy from the chemical.The author is inclined to support the later,and points out  if the theory is confirmed,there maybe other livings in elsewhere planet.

Why primitive livings could survive without photosynthesis?Because scientist found preserved fossil which shows having creatures living in the hydrothermal vents.Such kind of creatures ,they just utilize the mineral spurring out  from seabed or the chemical of the crust.

Further, recent movement excavates rocks from Quebec and find out that has passing resemblance to the bacteria in hydrothermal.More,the age of rocks date back to between 3.8 and 4.8 billion years ago which is earlier than the existent discovering photosynthesizing bacteria from 3.7 billion years old.So the only we have to prove is whether the rocks are real biochemical business or just a non-living geological process.If it confirmed,we could say hydrothermal theory form the very early creatures than any others.

And then science group analysis the rocks,and find it similar to younger pillow-shaped basalt from Hudson Bay formed when micro-organisms decayed. So we could believe the rocks from Quebec is fossil of bacteria.All above prove hydrothermal theory is convincing.