It is the point where the fibers of the retina leave the eye and become part of the optic nerve. It is the only part of the retina that is insensitive to light. At its center the porus opticus marks the point of entrance of the central artery of the retina.
By Andrew Alden. The lithosphere is the brittle outer layer of the solid Earth. The plates of plate tectonics are segments of the lithosphere. The lithosphere is basically the layer of the Earth that is strong enough to flex rather than flow. Its top is easy to seeit's at the Earth's surfacebut the base of the lithosphere is a transition rather than a sharp boundary.
Describe the process of plate tectonics. Give specific examples of geographic features created by plate tectonics. Plate tectonics is the movement of large portions of the crust. The movement is caused by magma squeezing out along the mid-oceanic ridges pushing the plates apart in a process called seafloor spreading.