If all the inner layers of the earth are firm solid what could have happened to Pangaea?

If all the inner layers of the Earth were solid, the tectonic processes that drive continental drift would be severely limited. Pangaea, which formed around 335 million years ago, could not have broken apart and drifted into the continents we see today without the movement of the Earth's lithosphere driven by the semi-fluid asthenosphere beneath it. Consequently, the absence of a dynamic, molten layer would likely mean that Pangaea remained a single supercontinent, unable to undergo the geological forces necessary for its fragmentation and the formation of separate landmasses.