[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
[01:32.14]which you do not see,
[01:34.00]it is very rarely that one comes across a dead body, except, of course, on the roads.
[01:41.03]They decompose and are quickly destroyed by the weather or eaten by some other creature
[01:48.57]It is almost always due to some very special circumstances that traces of land animals survive,
[01:55.47]as by falling into inaccessible caves, or into an ice crevasse,
[02:01.63]like the Siberian mammoths,
[02:03.85]when the whole animal is sometimes preserved, as in a refrigerator.
[02:09.58]This is what happened to the famous Beresovka mammoth
[02:13.45]which was found preserved and in good condition.
[02:17.24]In his mouth were the remains of fir trees--the last meal that he had before he fell into the crevasse and broke his back.
[02:25.79]The mammoth has now been restored in the Palaeontological Museum in St.Petersburg.
[02:32.42]Other animals were trapped in tar pits,
[02:34.95]like the elephants, sabre-toothed cats, and numerous other creatures that are found at Rancho la Brea, which is now just a suburb of Los Angeles.
[02:45.86]Apparently what happened was that water collected on these tar pits
[02:50.59]and the bigger animals like the elephants ventured out on to the apparently firm surface to drink,
[02:57.01]and were promptly bogged in the tar.
[03:00.12]And then, when they were dead, the carnivores,
[03:03.85]like the sabretoothed cats and the giant wolves,
[03:07.53]came out to feed and suffered exactly the same fate.
[03:11.71]There are also endless numbers of birds in the tar as well.