Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments.The Earth's magnetic field is somewhat caused by the composition of the earth's core which is rich in iron minerals. There is a solid inner core that is made of iron which makes up to 2/3 of the moon's size. The charged metal of the iron produces electric currents, consequently resulting to Earth's magnetic field.
Some isotopes, however, decay slowly, and several of these are used as geologic clocks. Dating rocks by these radioactive timekeepers is simple in theory, but the laboratory procedures are complex. <span>All methods rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age.</span>
<span>-The nervous system processes information from receptors that detect changes in the environment.
-The nervous system coordinates the systems of the body.
-The nervous system sends out appropriate responses to react to changes in the environment.
-The nervous system maintains homeostasis.</span>
