oxygenating atmosphere on acheron

The idea of using algae to assist in creating the appropriate atmosphere has occurred to me, but my concern there would be that it will take millions of years to reach the point that the atmosphere is breathable if algae are the only or even primary means of changing the atmosphere. You would need to seed the ocean and other major bodies of water, obviously, but it's going to take forever for them to reproduce enough to make a major difference, especially since a lot of the oxygen they produce is just going to be absorbed by the water anyway. It's only after the water reaches the saturation point with oxygen that it's really going to start entering the atmosphere.

Aquatic plants also would need to be down below the surface far enough to block out the ultraviolet light until an ozone layer had developed. Most likely the initial colonies of marine life will be in something like Sea World, with an eye toward eventually releasing the animals into the wild once the food chain has reached the point that it can support the larger animals. But with an ocean of the size we're talking about, I imagine we're talking about thousands of years without a major concerted effort.

I'm thinking some sort of apparatus would be needed that could be mounted on the continent's rocky surface, or rather embedded in the surface. I'm also imagining that if it's going to make any sort of progress in changing the atmosphere, it's going to move a tremendous volume of air in a very short period, kicking up whirlwinds everywhere, and probably igniting the gases in the current atmosphere as the oxygen is let loose.

Obviously not something our colonists will want to live right next to.

Probably they would be in a dome-covered hometown, maybe five square miles or so, so they can establish a farming ecology until they can open the dome or build other dome-covered habitats. But you're going to need a lot more than five square miles to establish a healthy, self-sustaining ecology.

As to the tigon question, my understanding is that tigons are one of the results of crossing tigers and lions. (The other being a liger.)

But am I correct in thinking that cheetahs, leopards and panthers also are capable of interbreeding with lions and tigers? I remember hearing a while ago that ecologists were distressed to discover that the Florida panther had gone extinct -- not by being hunted to death, but by interbreeding with other great cats so that the Florida panther genome no longer existed.

I remember talking the point with my high school biology teacher. If the basis for calling two animals different species is based solely on their appearance or the differing habitats they prefer, then they're not really separate species. They're just different breeds or populations of the same species, with perhaps different grooming or mating habits or a different social structure, but that's it. It's just sloppy taxonomy to insist on classifying them separately.