Wallace Line by the Sahul Shelf to New Guinea. The biogeographic boundary known as Lydekker's Line, which separates the eastern edge of Wallacea from the Australian region, has a similar origin to the Wallace line. During ice age glacial advances, when the , both Asia and Australia were united with what are now islands on their respective continental shelves as continuous land masses, but the deep water between those two large continental shelf areas was, for over 50 million years, a barrier that kept the flora and fauna of Australia separated from those of Asia. Wallacea consists of islands that were not
Front line Front line A front line (alternative forms: front-line or frontline) in military terminology is the position(s) closest to the area of conflict of an armed force's personnel and equipment, generally referring to maritime or land forces. When a front (an intentional or unintentional boundary) between opposing sides form, the front line is the area where the armies are engaged in conflict, especially the line of contact between the opposing forces. In a military conflict, then, when facing the front line, you face the enemy. All branches of the U.S. armed services use the related technical terms, Forward Line of Own