The tests used to determine whether brain stem death has occurred are outlined below: 1  A torch is shone into both eyes to see if they react to the light. 2  The cornea (transparent outer layer of the eye), which is usually very sensitive, is stroked with a tissue or piece of cotton wool to see if the eye reacts.
The inner core extends another 900 miles inward towards the center of the Earth. It is believed that this inner core is a solid ball of mostly iron, and nickel. The mantle is made of much denser, thicker material, because of this the plates float on it like oil floats on water.
The innermost is the core, the densest of the three layers. It is a spherical mass, composed largely of metallic iron, with smaller amounts of nickel and other elements. The middle layer is the mantle, made of dense, rocky matter. The outermost layer of the earth is the crust, which is the thinnet of the three layers.