PLANET EARTH Deserts
How do the cacti（cactus的复数，仙人掌） survive without rain? Hot winds suck all the moisture from the surface of the land. Clearly there must be something else that takes the place of rain. The secret is a cold sea current that runs parallel to the land. The cold water cools the moist warm air above it and that produces banks of fog. At the same time wind blowing on to the shore sweeps the fog inland.
Before long the cacti are dripping with dew（滴露）. The fog is so regular that moisture loving lichens（地衣，苔藓） are able to grow on the cacti and they absorb liquid like a sponge（海绵）. In the land of almost no rain these precious drops are life-savers for many different creatures. Further inland the air remains so warm that its moisture does not condense so this slender strip of desert is virtually the only part of the Atacama where life can exist.
Without the fog, this land, too, would be empty. The guanacos make the most of the dew but it will not remain for long. In an hour or two the sun will have burnt it off and dry the surface of the cacti. The Sonoran（索诺兰沙漠，位于加利福尼亚） desert in Arizona（亚利桑那州） is not quite so dry as the Atacama - some rain does fall. But it is infrequent and when it does arrive animals and plants have to be ready to make the most of it. And it's coming.
