Answer:
they are not affected by earth atmosphere
Protection of certain species is a very controversial topic. Many species like the mountain lion or jaguar that are near extinction in certain areas, are threats to human life. Another reason is that they could off set the food chain when they come back and be stonger than ever. For example the mountian lion could eat out the thriving white tail deer population which was struggling because of the mountain lion. And many people rely on white tail deer for food.
Hope this helped :)
Tar sands pits , sorry if I got this wrong
Absence of oxygen
fermentation is an anaerobic (meaning doesn't require oxygen) process
