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.
Sediments of nearly identical age had been found previously from the Deep Sea Drilling Project Hole 534A, located on the Blake-Bahama basin in the central Atlantic. These sediments and the rocks on which they rest are among the oldest oceanic crust found in the world ocean. There is a more-detailed discussion at Site 801: Sedimentology and Biostratigraphy share | improve this answer