Earth Atmosphere is relatively thin shell. Half the mass of the atmosphere is within 5 Km (3.1 miles) of the surface, and 90 percent is within (12.4 miles). Twenty km is not very far-about a 10-minutes drive on most interstate highways. By comparison Earth's radius is 6,378 km (3963 miles).
Question 1: What percent of the Earth's radius is 20 kilometers?