Scientific consensus supports the idea that living organisms require oxygen. Then, a scientist discovers a type of bacteria that metabolizes sulfur instead of oxygen, and thus survives in environments without oxygen. The scientist concludes that a diverse group of many different organisms could live in an oxygen-free environment.
The reason why some scientist should be skeptical of the scientist’s results and conclusion is to evaluate experimental procedures and it also helps scientists recognize when ideas are not supported by evidence. This is the way that this theory can become a scientific consensus.
I hope it helps, Regards.