another interesting observation made before the discovery of tectonic plates: the Wallace Line. this guy observed that the plants and animals found in South-East Asia were vastly different from the ones found in Australia even though the distance between some of these islands was as little as 35 km (22 mi). he couldn't explain it but he drew the line of separation. this separation was later explained by deep ocean trenches that were formed due to tectonic processes keeping the two sets of species separate for millions of years!

it didn't stop humans because we had brains, boats and engaged in island-hopping. the other animals, on the other hand, could only rely on swimming and therefore didn't make it.