新概念英语第四册在线练：The past life of the earth
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The past life of the earth
(相关资料图)
地球上的昔日生命
It is animals and plants which lived in or near water whose remains are
most likely to be preserved, for one of the necessary conditions of preservation
is quick burial, and it is only in the seas and rivers, and sometimes lakes,
where mud and silt have been continuously deposited, that bodies and the like
can be rapidly covered over and preserved. But even in the most favourable
circumstances only a small fraction of the creatures that die are preserved in
this way before decay sets in or, even more likely, before scavengers eat them.
After all, all living creatures live by feeding on something else, whether it be
plant or animal, dead or alive, and it is only by chance that such a fate is
avoided. The remains of plants and animals that lived on land are much more
rarely preserved, for there is seldom anything to cover them over. When you
think of the innumerable birds that one sees flying about, not to mention the
equally numerous small animals like field mice and voles which you do not see,
it is very rarely that one comes across a dead body, except, of course, on the
roads. They decompose and are quickly destroyed by the weather or eaten by some
other creature.
只有生活在水中或水边的动植物尸体最有可能被保存下来，因为保存的必要条件之一是迅速掩埋，所以只有在泥沙不停淤积的海洋和江河里，有时在湖泊里，尸体之类的东西才能被迅速地覆盖而保存下来。
即使是在最有利的环境中，死去的生物中也只有一小部分能在开始腐烂前，或更可能在被食腐动物吃掉之前，被这样保存下来。因为一切生物都是靠吃别的东西来活命的，不管这种东西是植物还是动物，死的还是活的，因此，生物偶尔才能避免被吃掉的命运。曾在陆地上生活过的动植物的遗体被保存下来的更为罕见，因为陆地上几乎没有什么东西覆盖它们。你可以想象出天上有看得见的飞来飞去、数不清的鸟，地上有不显眼的无数的老鼠和田鼠之类的小动物，但是，除非在路上，很少有人遇到这些动物的尸体，因为它们****之后很快就被风化掉，或被别的动物吃掉了。
New words and expressions 生词与短语
preservation
n. 保存
silt
n. 淤泥
scavenger
n. 食腐动物
vole
n. 野鼠，鼹鼠
decompose
v. 腐烂
inaccessible
adj. 不能到达的
crevasse
n. 缝隙
Siberian
adj.西伯利亚的
palaeontological
adj. 古生物学的
St. Petersburg
n. 圣彼得堡
sabre-toothed
adj. 长着锐利的长牙
venture
v. 冒险
bogged
adj. 陷入泥沼的，陷入要困境的
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