Into the Giant Landmass (One Shot)

Rica, Ermie, Roan, Kiel and Dan decided to have an expedition to explore the continent of Africa. While travelling through the Atlantic Ocean, something went wrong making them to the coast of the historical Pangaea. In this supercontinent, they will experience a lot, and the strange place would be a mystery for them.

What would they do if they discovered about it?
What would be the cause for this to happen?
How would they know that the expedition they all planned ended into a giant landmass?