MARS
Mars According to the best evidence gathered by space probes and astronomers, Mars is an inhospitable planet, more similar to Earths Moon than to Earth itself - a dry, stark, seemingly lifeless world. Mars air pressure is equal to Earths at an altitude of 100,000 feet. The air there is 95% carbon dioxide. Mars has no ozone layer to screen out the Suns lethal radiation. Daytime temperatures may reach above freezing, but because the planet is blanketed by the mere wisp of an atmosphere, the heat radiates back into space. Even at the equator, the temperature drops to 50 ℃ at night. Today there is no liquid water, although valleys and channels on the surface show evidence of having been carved by running water. The polar ice caps are made of frozen water and carbon dioxide, and water may be frozen in the ground as permafrost. Despite these difficult conditions, certain scientists believe that there is a possibility of transforming Mars into a more Earth like planet. Nuclear reactors might be used to melt frozen gases and eventually build up the atmosphere. This in turn could create a greenhouse effect that would stop heat from radiating back into space. Liquid water could be thawed to form a polar ocean. Once enough ice has melted, suitable plants could be introduced to build up the level of oxygen in the atmosphere so that, in time, the planet would support animal life from Earth and even permanent human colonies. This was once thought to be so far in the future as to be irrelevant, said Christopher McKay, a research scientist at the National Aeronautics and Space Administration. But now its starting to look practical. We could begin work in four or five decades. The idea of terra forming Mars, as enthusiasts call it, has its roots in science fiction. But as researchers develop a more profound understanding of how Earths ecology supports life, they have begun to see how it may be possible to create similar conditions on Mars. Dont plan on homesteading on Mars any time soon, though. The process could take hundreds or even thousands of years to complete, and the cost would be staggering.
分词作补语的语法应用
be interested doing/to do的区别
cease doing/to do的区别
分词作插入语的语法应用
forget doing/to do的区别
一般过去时的用法
现在完成时的定义
mean to doing/to do的区别
连词+分词(短语)的语法应用
不定式中省略to的情况
用一般过去时代替完成时的应用
介词to的用法
将来完成时的应用
since的四种用法
分词作表语的语法应用
过去完成时的应用
一般现在时的用法
独立主格结构
过去式和现在完成时的区别
不定式作定语的语法解析
try doing/to do的区别
不定式作状语的语法应用
begin(start) doing/to do的区别
过去分词作宾语补足语的语法解析
分词的时态
be to和be going to的区别
不定式的时态和语态
since和for的区别
go on doing/to do的区别
延续动词与瞬间动词的区别
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