The porcelain layer is attached to the metal and makes the crown look like a regular tooth. In comparison, the all-porcelain or all-ceramic crown does not have the layer of metal as part of the crown. The porcelain itself is what goes onto your tooth.
Quick Answer. An abyssal plain is a deep undersea area created by sediments overlaying a rocky crust, and they are the flattest places on Earth. Abyssal plains cover one-third of the Earth's surface, as much as all land above water, and they sit near continental borders and underwater mountain ranges.
Rift Valley in East Africa\Great Rift Valley. Back to Online Encyclopedia Index. Image Ownership: Public Domain. Site of some of the oldest hominid fossils, The Great Rift Valley in East Africa refers to a massive land depression, formed approximately twenty million years ago when two parallel fault lines pulled apart.