英语翻译Earth is an ocean planet.About three billon years ago,li

英语翻译
Earth is an ocean planet.About three billon years ago,life on our planet began in the deep blue seas.Ninety-nine percent of the living space on
earth is in oceans.Marine life is incredibly rich and varied.There are about five million species in the
oceans and we
have yet to learn much about them.Life in the oceans ranges from the tinest plankton all
the way up to giants like sharks and whales.What makes the ocean such a great place to
live?The answer is water.
CHEWICAL STRUCTRE
The chemical structure of water makes it an excellent medium for life.Water is actually
quite simple,bus the way the water molecule is formed gives water its unique properties.
The water molecule is made up of two hydrogen atoms and ane oxygen atom.They form a polar
molecule,thet is,one with a slightiy positily positive end and a slightly negative end.
Because water is polar,it can break dowm both solids and gases.The nutrients in whatever
falls into the ocean quickly become available to other livling creatures.The chemical
structure of water also makes it different from almost everything else on earth.Water is
a liquid at room temperature and has a relatively high hreezing point.
When dissovied gases and solids mix with pure water,the result is sea water,
or salt water.The salinity of the earth's oceans is about thirty-five parts for thousand,
meaning that thjere are about thirty-five grammes of dissolved solids and gasses in one
kilogramme of water.Even though the pure water is what gives sea water its main properties,
the salinity of sea water affects both its weight and freezing point.Salt water has a lower water
freezing point and is heavier than pure water.
DENSITY
Density is the relationship between mass and volume and is measured in kilogrammesper
cubic metre.The density of pure water is 1,000kg/m3,meaning that one cubic water of water
weighs one thousand kilogrammes.If a substance has a higher density,say 5,000kg/m3,it will not flout on water.Marine animals and plants take
advantage of density of the water.with the right kind of body,it is possible
to flout around in the ocean and let the water do the work.When water
freezes,its density decreases.If it did not,the oceans would be frozen solid.
OCEAN MOTION
Since changes in salinity and temperature affect water's density,the water in the ocean is always moving.Dense water sinks and less dense
water is pushed to the surface.This circulation adds energy to the marine ecosystems and moves nutrients around.
Isn't it amazing that a singlesubstance can be so important to our planet and even the whole universe?Water ,which seems sosimple and common,is what makes time possible.Of all the resources on earth-oil,gas ,gold and so on-nothing is as precious of a drop of rain.Learing about the
properties of water helps us understand life on our plnet.The most important thing 0wecan learn about water,hower,is that we must protect it and use it wisety.Our future depends on it.

地球是一个海洋星球.约三十亿年前,生命在地球上深蓝色的海里就开始产生了.地球上百分之九十九的生命都生活在海洋.海洋生物丰富多样.海洋里大约有五百种生物,还有很多有待于我们
进一步了解.海洋里的生物极为广泛,小到浮游生物,大到巨大动物如鲨鱼和鲸鱼.是什么使海洋成为孕育生命的理想地方呢?答案是水.
CHEWICAL STRUCTRE化学结构
水的化学结构使它成为绝佳的生命存在的介质.水实际上很简单,但水分子的结构方式却赋予水独特的性质.水分子是由两个氢原子和一个氧原子构成.他们形成了一个极性分子,那就是,一端为正极,一端为负极.因为水是极性的,因此它能分开固体和气体.无论什么营养只要一进入海洋就迅速成为其它生物营养.水的化学结构几乎区别于地球上的所有其它物体.水在室温下是液体并具有相对较高的冰点.当溶于水的气体和固体与纯净水混合后结果是海水或盐水.地球海洋里的盐度大约35,这就是说每公斤水中约含有35克溶解的固体和气体在水中.即使纯水使海水具有了水的主要性质,然而海水的盐度却影响了它的重量和冰点.海水冰点较低,比重也比纯水重.
密度
密度是用来衡量每立方米物质的质量和体积之间的关系的.纯净水的密度是每立方米1,000千克,意思是每立方水的水重1000千克.如果一种物质密度较高,比如说5,000kg /立方米,它将不会浮在水面上.海洋动物和植物利用了水的密度的特点,形成了适合的自身体型,借助于水,在海洋里到处游动.,这是不可能的事在海洋中,工作量,让水做这项工作.当水结冰时,其密度的减小（注：结的冰浮在水面上）,否则,海洋将会被冻成固体了.