AFOQT Practice Test

The correct answer focuses on the characteristics of the exosphere, which is the outermost layer of Earth's atmosphere. The exosphere begins at a height of approximately 6,200 miles (or about 10,000 kilometers) above the Earth's surface and extends into outer space. This layer is significant because it contains extremely thin air and is where atmospheric particles are so sparse that they can travel hundreds of kilometers without colliding with one another.

In contrast to this, the other features mentioned highlight aspects of different layers of the atmosphere. Weather phenomena arise in the troposphere, which is much closer to the Earth’s surface. The densest layer of the atmosphere is the troposphere as well, where most of the atmospheric mass is concentrated. Additionally, commercial flights typically operate within the lower parts of the atmosphere, specifically within the troposphere. Hence, the exosphere, characterized by its high altitude and low density, is distinctly defined by features such as the starting point of its altitude.