The statements provided in the passage support the conclusion that:
(C) A thorough survey of a planet's surface is insufficient to establish beyond a doubt that the planet contains no life.
The passage presents examples of microbial life existing in extreme environments on Earth that are not dependent on energy from sunlight. These examples include microbial life in bedrock deep below the surface and bacteria on the deep ocean floor feeding on gases from the Earth's interior. These findings suggest that life can exist in unexpected and unconventional habitats. Therefore, a thorough survey limited to the planet's surface may not be sufficient to conclude definitively that there is no life on a given planet. There could be life forms existing in environments or conditions that are not immediately observable or accessible through surface exploration.
Options (A), (B), (D), and (E) either go beyond the scope of the information provided in the passage or do not directly relate to the conclusion supported by the passage.