According to the text, the sun’s mass is about 2 × 10³⁰ kg and it loses about 4 × 10⁹ kg per second as its hydrogen is converted into helium. Assuming that the sun has been radiating energy at the same rate as today during the 4.5-billion-year existence of the earth, what percentage of its mass has been lost in this period? What does this imply about the possibility that the intensity of solar radiation has been roughly constant during the life of the earth, as geological evidence suggests?