The layer with the least pressure is the exosphere. Pressure decreases as altitude increases because gravity pulls atmospheric air towards the Earth's surface. The higher you go, the less air mass there is above you, resulting in lower pressure.
Understanding Atmospheric Pressure
Atmospheric pressure is the force exerted by the weight of air above a given point. This pressure is highest at sea level where the entire column of air above exerts its weight. As we ascend into the atmosphere, the amount of air above decreases, leading to a corresponding decrease in pressure.
Several sources confirm this:
- Exosphere: The exosphere is the outermost layer of Earth's atmosphere and consequently has the lowest pressure. [Exosphere](Reference 1) explicitly states that pressure drops as altitude increases due to gravity pulling air towards the Earth's surface.
- Thermosphere: While some sources suggest the thermosphere, this is incorrect. The thermosphere has extremely low density, but it still has a measurable pressure, far greater than the exosphere. [Solved: Which layer of Earth's atmosphere has the lowest pressure](Reference 8) highlights the common misconception that it has the lowest pressure, while incorrectly stating it has the lowest pressure.
- Altitude and Pressure: The relationship between altitude and pressure is consistent across different atmospheric layers. As altitude increases, pressure consistently decreases. [Air Pressure](Reference 6) clearly explains how increasing elevation leads to a decrease in air molecule density and therefore pressure.
The question needs clarification to specify whether it refers to the Earth's atmosphere or other contexts (e.g., layers of the Earth itself or blood vessels). The above answer addresses the atmospheric layer with the least pressure.
