Good question! I'm wondering how you could do a final scoring round when every player species is made extinct. There are no map animals and no cultures, so that leaves the fossil record and the Tarpit tiles. Do you divide the Tarpit tiles according to the tiebreakers? I don't know.
I may be missing something - is there something in the rules that says all species go extinct when the games reaches Hothouse or Snowball Earth? When I've played Snowball Earth has left biomes and species on the map - and a lot of tiles in the tarpit (hence the query about scoring).
Extinctions may occur through biome displacement (caused by the catastrophe that triggered Hothouse/Snowball Earth), but I'm not sure that everything dies?