Final answer:
Laurentia, Baltica, and Avalonia combined to form Laurasia, one of the supercontinents that later joined to create Pangaea, and is distinctly different from Gondwana which consisted of the southern continents.
Step-by-step explanation:
Laurentia, Baltica, and Avalonia combined to form Laurasia. During the Paleozoic Era, continent formation was a dynamic process involving the collision and separation of landmasses. Laurentia was a major craton that became the foundation of North America and Greenland. Baltica primarily underlies Scandinavia, and Avalonia was a microcontinent. Their collision resulted in the formation of the supercontinent known as Laurasia. This formation was part of the larger cycle of supercontinent assembly which eventually led to the formation of Pangaea. Laurasia consisted of the northern continents present in today’s Northern Hemisphere and is distinctly different from Gondwana, which was the southern counterpart comprising today's Southern Hemisphere continents such as Australia and Africa. The Appalachian/Caledonide Mountains were formed over a period due to different tectonic events including the Caledonide Orogeny which is associated with the closure of the Iapetus Ocean.