The atmosphere above each square centimeter of Earth’s surface weighs 1 kilogram (kg).

a. Assuming Earth is a sphere of radius R = 6,440 km, use the formula S = 4πR² to calculate the surface area of Earth and then find the total mass of the atmosphere.

b. Oxygen occupies approximately 22% of the total mass of the atmosphere, and it is estimated that plant life produces approximately 0.9 × 10¹³ kg of oxygen per year. If none of this oxygen were used up by plants or animals (or combustion), how long would it take to build up the total mass  of oxygen in the atmosphere [part (a)]?*