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17 Into the Troposphere
第十七章 進入對流層
Thank goodness for the atmosphere. It keeps us warm. Without it, Earth would be a lifeless ball of ice with an average temperature of minus 60 degrees Fahrenheit. In addition, the atmosphere absorbs or deflects incoming swarms of cosmic rays, charged particles, ultraviolet rays, and the like. Altogether, the gaseous padding of the atmosphere is equivalent to a fifteen-foot thickness of protective concrete, and without it these invisible visitors from space would slice through us like tiny daggers. Even raindrops would pound us senseless if it weren't for the atmosphere's slowing drag.
謝天謝地，我們有了大氣。它使我們有了個溫暖的環境。沒有大氣，地球會是個沒有生氣的冰球，平均溫度只有零下50攝氏度。而且，大氣吸收或擋開大盤射來的宇宙射線、帶電粒子、紫外線等等。總的來說，厚厚的大氣相當于4.5米厚的保護性混凝土，沒有它，來自太空的這些無形訪客會像小小的匕首那樣捅進我們的身體。沒有大氣的牽制作用，連雨點也會把我們打昏在地。
The most striking thing about our atmosphere is that there isn't very much of it. It extends upward for about 120 miles, which might seem reasonably bounteous when viewed from ground level, but if you shrank the Earth to the size of a standard desktop globe it would only be about the thickness of a couple of coats of varnish.
最引人注目的是，我們的大氣并不很多。它往上伸展至大約190公里處，從地面上看，它也許顯得很多，但如果把地球縮小到書桌上地球儀的大小，大氣不過是大約一兩層漆的厚度。
For scientific convenience, the atmosphere is divided into four unequal layers: troposphere, stratosphere, mesosphere, and ionosphere (now often called the thermosphere). The troposphere is the part that's dear to us. It alone contains enough warmth and oxygen to allow us to function, though even it swiftly becomes uncongenial to life as you climb up through it.
科學上為了方便起見，把大氣分成4個厚度不等的層次：對流層、平流層、中間層和電離層（現在往往又稱熱層）。對流層對我們來說是個十分寶貴的部分。僅對流層包含的熱量和氧氣就足以使我們活下去，雖然你往上穿越對流層的時候，它很快會變成一個對生命來說是不合意的地方。
