[ti:δ֪]
[ar:]
[al:]
[by:http://www.lrc.com.cn]

[00:01.77]Lesson 26
[00:03.99]The past life of  the earth
[00:11.42]What is the main condition for the preservation of the remains of any living creature
[00:19.67]It is animals and plants which lived in or near water
[00:23.56]whose remains are most likely to be preserved,
[00:26.54]for one of the necessary conditions of preservation is quick burial,
[00:31.62]and it is only in the seas and rivers, and sometimes lakes,
[00:35.79]where mud and silt have been continuously deposited,
[00:39.34]that bodies and the like can be rapidly covered over and preserved.
[00:45.03]But even in the most favourable circumstances
[00:47.76]only a small fraction of the creatures that die are preserved in this way
[00:52.70]before decay sets in or,even more likely, before scavengers eat them.
[00:58.75]After all,all living creatures live by feeding on something else,
[01:03.74]whether it be plant or animal,dead or alive,
[01:07.49]and it is only by chance that such a fate is avoided.
[01:12.59]The remains of plants and animals that lived on land are much more rarely preserved,
[01:18.04]for there is seldom anything to cover them over.
[01:22.05]When you think of the innumerable birds that one sees flying about,
[01:26.30]not to mention the equally numerous small animals like field mice and voles
[01:31.70]which you do not see,
[01:33.33]it is very rarely that one comes across a dead body,except,of course,on the roads.
[01:40.52]They decompose and are quickly destroyed by the weather or eaten by some other creature
[01:47.95]It is almost always due to some very special circumstances
[01:51.95]that traces of land animals survive,
[01:54.75]as by falling into inaccessible caves,or into an ice crevasse,
[02:01.47]like the Siberian mammoths,
[02:03.60]when the whole animal is sometimes preserved,as in a refrigerator.
[02:09.22]This is what happened to the famous Beresovka mammoth
[02:13.28]which was found preserved and in good condition.
[02:17.02]In his mouth were the remains of fir trees--
[02:20.24]the last meal that he had before he fell into the crevasse and broke his back.
[02:25.50]The mammoth has now been restored in the Palaeontological Muse-um in St.Petersburg.
[02:32.06]Other animals were trapped in tar pits,
[02:34.65]like the elephants,sabre-toothed cats,and numerous other creatures
[02:39.41]that are found at Rancho la Brea,which is now just a suburb of Los Angeles.
[02:45.29]Apparently what happened was that water collected on these tar pits
[02:50.04]and the bigger animals like the elephants
[02:52.74]ventured out on to the apparently firm surface to drink,
[02:56.53]and were promptly bogged in the tar.
[02:59.77]And then,when they were dead,the carnivores,
[03:03.21]like the sabretoothed cats and the giant wolves,
[03:06.75]came out to feed and suffered exactly the same fate.
[03:11.10]There are also endless numbers of birds in the tar as well.