Hate to continue the chain, but on the off-chance government organisations know more than they're letting on, we might need to extend that to "most humans". Though, in that case, it might have to be "thought by most humans"? Just speculating for the hell of it. e.g.,
Fixed: Earth is known by most humans as the only planet to have life.
Fixed: Earth is known by most humans as the only planet to have life.