Basically the title. They’re going to encounter animals they’ve never seen before, or notice a complete lack of familiar animals. They’re going to notice the none of the plants are the same, and that there aren’t any domesticated plants other than what they may be carrying. They might try to go back the way they came and find it impossible.
I had a similar realization when rewatching 03x04 Who Watches The Watchers. Those Mintakans would eventually realize they are unrelated to every other life form on the planet.
They might even have legends of a man in the sky promising them a new world, now a theory to be wholly supported by the biological record x_x