[ar:MP3 同步字幕版(英音)]
[ti:The Past Life of the Earth]
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[00:01.51]Lesson 26
[00:03.68]The past life of the earth
[00:12.17]What is the main condition for the preservation of the remains of any living creature?
[00:19.84]It is animals and plants which lived in or near water whose remains are most likely to be preserved,
[00:26.93]for one of the necessary conditions of preservation is quick burial,
[00:31.97]and it is only in the seas and rivers, and sometimes lakes,
[00:36.10]where mud and silt have been continuously deposited,
[00:39.68]that bodies and the like can be rapidly covered over and preserved.
[00:45.37]But even in the most favourable circumstances
[00:48.33]only a small fraction of the creatures that die are preserved in this way
[00:52.96]before decay sets in or, even more likely, before scavengers eat them.
[00:59.09]After all, all living creatures live by feeding on something else,
[01:04.21]whether it be plant or animal, dead or alive,
[01:08.09]and it is only by chance that such a fate is avoided.
[01:12.95]The remains of plants and animals that lived on land are much more rarely preserved,
[01:18.68]for there is seldom anything to cover them over.
[01:22.41]When you think of the innumerable birds that one sees flying about,
[01:26.84]not to mention the equally numerous small animals like field mice and voles