I was talking to a gormist, and he stopped the debate by stating that the early earth with the 20% methane was pure greenhouse effect (too hot), and then when the methane went away we got the Snowball Earth which froze everything. This is typical 'efficient debating' which the trumpies and gormies use to win. However, the facts are totally wrong. Never debate with these guys!
Even though the methane eating bacterial mats showed up a billion years or so ago, there must have been at least a billion years of organic molecules fighting it out in the seas. This has to be true, unless we want to bring in Galactic Seeders. As usual, we shall trot out the Scientific Method.
Hypothesis - In the shirtsleeve temperatures of Methane Earth, random organic molecules appeared. They fought the good fight of Evolution, by eating each other and improving.
Physics - Under the right conditions, molecules can 'reproduce' simply by seeding. This is shown by ice in super-cooled water. Introduce, the tiniest speck with the right surface, and suddenly the whole tank turns to ice. We can venture into a thought experiment of the early earth, full of unorganized organic molecules. Suddenly, one molecule can seed, and we get a growing blob of concentrated energy. Different blobs fight for dominance by running into each other. The best blob wins. And so on. Inside each blob are the conditions for more 'accidents' in seeding. A billion years later, dna takes over the world.
Verification - Totally can't happen, since the successors ate the previous generations. Once dna got into evolution, the record was wiped. We might get a hint by looking at comets, and such.
ps. With this hypothesis, somebody could put some money into soft-tissue fossils. The concept being that pre-bacteria shale layers might have a spray of organic residue that can only be seen with the best atomic force microscopes. Wouldn't that be something!
pps. Instead of 3d seeding, you could also have linear chain seeding, with everything tangling, and seeding at the end point. At the other end, in the centre, you would have an active point for mutation. Would make a fascinating computer game. :) Reproduction would be done by tearing apart the blobs by active tidal forces making strong currents, leaving a whole bunch of active points.