I think fermentation and radioactive beaches are my favorites. From a thematic perspective, I don't have the brains to actually have an opinion on whats most likely or correct.
Fermentation is funny & resonates with how fermentation is the most important chemical process to civilization
Radioactive beaches are nice if we ever manage to destroy all life in thermonuclear war, dust to dust, radioactive beaches to radioactive beaches.
edit: Creation Myths are acceptable
On earth, there are two lines. One started from a single cell organism that is the common ancestor to nearly all life. The other is the okapi, which emerged fully formed through a miraculous and astronomical coincidence in 1845. It has no known relatives on earth.