Why do winds form in the Earth's atmosphere?

Winds form in the Earth's atmosphere primarily due to the movement of air caused by differences in temperature and pressure. When air is heated, it becomes less dense and rises, creating an area of low pressure. Conversely, cooler air is denser and will sink, resulting in areas of high pressure. This dynamic creates air movement as air moves from high-pressure areas to low-pressure areas in an effort to equalize the pressure. Thus, the correct choice highlights the fundamental principle of thermodynamics and fluid dynamics, which governs the behavior of air masses and the formation of wind patterns in the atmosphere.

The other options do not address the primary cause of wind formation. For example, the statement about pressure systems being nonexistent contradicts the very nature of how wind is generated, as winds are fundamentally driven by pressure differentials. Similarly, stating that ocean currents are stable does not address the complexities of atmospheric conditions that lead to wind. Finally, the flatness of Earth's surface does not play a significant role in wind formation; rather, it is the interaction of temperature and pressure that is key.