| gamma ray
|| n. 地面
- Earth’s atmosphere changes as altitude increases, with significant differences occurring in composition, electrical charge, pressure, and temperature.
- The atmosphere is divided into layers, from the troposphere, the lowest level, to the exosphere, more than 300 miles above Earth’s surface.
- The atmosphere, which is a thin layer of gases, insulates the surface from temperature extremes and protects Earth from most space debris and from dangerous radiation such as gamma rays. Nearly all atmospheric gases are within about 20 miles of Earth; weather occurs within 10 miles.
- In the troposphere, from the surface to about six miles above Earth, temperature declines with altitude because the primary heat source for the air is the ground.
- Most weather is confined to the troposphere because it holds more than 95 percent of water vapor and 80 percent of all atmospheric gases.
- The top of the troposphere’s boundary with the stratosphere is called the tropopause. At the tropopause, temperatures begin to increase because the ozone layer warms the air.