When Ulysses comes across a planet that looks like Earth, but is still in the Ice Age, he goes down in a shuttle to check it out. What he finds is that it is actually Earth from the past, and also finds winged people that are in hybernation.
When a woman wakes up, she tells Ulysses about what has gone on etc. They are attacked by the Keekenopters, vulture-like birds that fire lasers from their beaks.
The base that they are in is actually a large ship, and as the ice breaks, it begins to sail.
It is one of my favourite episodes, which is very well animated, written and has lots of action. Especially when the Keekenopters attack and Ulysses and the children are surrounded by them. Check it out now.