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.
Geologists hypothesize that the Earth's center is composed of predominantly iron. The outer portion of the center, known as the outer core, is thought to be liquid iron. While the interior portion of the center, known as the inner core is thought to be solid iron. This hypothesis is based upon two important observations. First, energy waves known as shear waves do not travel through the outer core. Secondly the Earth has a magnetic field.