Which of the following is NOT a layer of the Earth's atmosphere?

The hydrosphere is not considered a layer of the Earth's atmosphere. Instead, it refers to all the water on Earth, encompassing oceans, rivers, lakes, and even water vapor in the atmosphere. In contrast, the atmosphere itself is composed of several distinct layers, including the stratosphere, troposphere, and mesosphere.

The troposphere is the lowest layer of the atmosphere where most weather phenomena occur, and it contains the highest concentration of air mass. Above it lies the stratosphere, which contains the ozone layer that protects the Earth from harmful ultraviolet radiation. The mesosphere is found above the stratosphere, stretching to higher altitudes where temperatures begin to decrease again.

Understanding the distinction between the hydrosphere and the atmospheric layers is crucial for grasping earth science and environmental studies, as these components play different roles in Earth's systems.