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.
Origin of Sand Dunes. The origin of sand dunes is very complex, but there are three essential prerequisites: An abundant supply of loose sand in a region generally devoid of vegetation (such as an ancient lake bed or river delta) A wind energy source sufficient to move the sand grains. A topography whereby the sand particles lose their momentum and settle out. Any number of objects, such as shrubs, rocks or fence posts can obstruct the wind force causing sand to pile up in drifts and ultimately, large dunes.