Trace amounts of radioactivity in surface rocks reveal that the Earth s age is about 4.5 billion years. Radioactive material also heats its interior.
Currents created by motions in the Earth s core generate the Earth s magnetic field .
That field in turn affects the motion of charged particles in the upper atmosphere. Such particles may create auroral displays when they collide with oxygen and nitrogen in the upper atmosphere. The nitrogen, carbon dioxide, and water of our atmosphere may have come from volcanic gases vented over the Earth s history. Alternatively, these atmospheric gases may be the evaporated remains of comets that hit the Earth in its infancy. Plant life has created the atmosphere s oxygen by photosynthesis.