These early population groups originally lacked watercraft technology, and thus could only cross narrow interisland seas with primitive floats or rafts (likely bamboo or log rafts) or through accidental means. Especially the deeper waters of the Wallace Line, Weber Line, and Lydekker Line with islands disconnected from mainland Asia even in the lower sea levels of the last glacial period. They settled in what are now islands mostly through land migrations into the coastal lowland plains of Sundaland and Sahul, most of which are now underwater.