Question

Consider the following statements about the Earth's atmosphere:

I. The majority of atmospheric air is concentrated within the first 32 km from the surface.

II. Outer space officially begins at an altitude of 50 km.

III. Gravity is the force that holds the atmosphere around the Earth.

Which of the statements above are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. I, II, and III

Answer 1

Answer:

D. I, II, and III

Earth's Atmosphere

• Concentration of Air: Approximately 80% of the Earth's atmospheric mass is found within the lowest 32 kilometers (about 20 miles) above the surface. This is due to the pull of gravity.

  • The troposphere, the lowest layer where weather occurs, contains about 75% of the atmosphere's mass and nearly all of its water vapor.

  • The stratosphere, which contains the ozone layer, extends up to about 50 km.

• Boundary of Outer Space: The Kármán line, at an altitude of 100 kilometers (62 miles) above sea level, is widely recognized as the boundary between Earth's atmosphere and outer space.

  • This definition is used by the Fédération Aéronautique Internationale (FAI), the world governing body for air sports and aeronautical world records.

  • While some sources might use different altitudes for specific purposes, 100 km is the most commonly accepted international standard.

• Role of Gravity: Gravity is the fundamental force responsible for holding the Earth's atmosphere in place. It pulls the air molecules towards the center of the planet, preventing them from escaping into space. Without gravity, the atmosphere would dissipate.

  • The density of the atmosphere decreases significantly with increasing altitude because of this gravitational pull and the expanding volume.