Passage Summary: A biologist argues that because ancient fossilized bacteria were already complex, they must have been evolving for a long time. This means life started very early on Earth when things were still pretty rough, suggesting life can pop up in difficult environments elsewhere too.

Conclusion: Life might be able to emerge under various harsh conditions across the universe.

Reasoning: Fossilized bacteria from 3.5 billion years ago were complex, implying a long prior evolution. Given Earth's age of 4.6 billion years, life must have started shortly after the planet formed during a very harsh period.

Analysis: The claim that the bacteria must have had a long evolutionary history acts as an intermediate conclusion. It is derived from the observation that the fossils were 'quite complex,' and it is then used to support the further claim that life appeared very soon after Earth's formation. When identifying roles, notice how this statement serves as a bridge: it's a 'child' of one premise and a 'parent' to the next. It isn't the main point of the whole passage, but it's a vital stepping stone to get there.