Final answer:
Fifty percent of the atmospheric gases are found below 6.5 miles (10 kilometers), which is the approximate height of the troposphere, the lowest layer of Earth's atmosphere.
Step-by-step explanation:
The question you're asking relates to the composition and structure of the Earth's atmosphere. Fifty percent of the gases making up the atmosphere are found below approximately 6.5 miles or about 10 kilometers (km). This troposphere is the lowest layer of the atmosphere and extends from the Earth's surface up to about 6 miles or 10 km in altitude. It contains the vast majority of the atmosphere's mass and is where virtually all weather events and human activities take place.