Biologist: Scientists have discovered fossilized bacteria in rocks 3.5 billion years old. The fossils indicate that these bacteria were quite complex and so must have already had a long evolutionary history when fossilized 3.5 billion years ago. However, Earth is only 4.6 billion years old, so the first life on Earth must have appeared soon after the planet’s formation, when conditions were extremely harsh. This suggests that life may be able to arise under many difficult conditions throughout the universe.

Which one of the following most accurately describes the role played in the biologist’s argument by the claim that the fossilized bacteria discovered in rocks 3,5 billion years old must have had a long evolutionary history?