MCQ Detailed View

The Earth’s atmosphere is divided into several layers based on temperature and composition. These include the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The exosphere is the outermost layer, beginning at about 690 kilometers above the Earth’s surface and extending outward to nearly 10,000 kilometers.

In the exosphere, air is extremely thin, and molecules are so far apart that they rarely collide. Instead of behaving like a continuous fluid, gas particles move almost freely and can even escape Earth’s gravity if they reach escape velocity. Because of this, the exosphere forms the transition zone between Earth’s atmosphere and outer space.

The exosphere is made up mainly of hydrogen and helium atoms, with traces of oxygen, nitrogen, and carbon dioxide. Unlike the lower layers, it does not have a clear boundary; it gradually thins into space. Satellites orbit within this layer because air resistance is nearly nonexistent.

If we compare the other layers:

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  The troposphere (0–12 km) is where weather occurs.

  
  


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  The stratosphere (12–50 km) contains the ozone layer.

  
  


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  The mesosphere (50–85 km) is where meteors burn up.

  
  


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  The thermosphere (85–690 km) has auroras and very high temperatures.

  
  

Beyond the thermosphere lies the exosphere, which is why it covers the altitude range given in the question.

Thus, the correct answer is Exosphere, the highest atmospheric layer extending from about 690 km up to 10,000 km above Earth, where the atmosphere merges into space.