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Figure 01d Cambrian Period [view large image] |
problematical forms that cannot definitely be assigned to well established taxa. They include virtually all the groups known from the Burgess Shale and other Middle Cambrian localities, thus compressing the available time for the morphological diversification of metazoans, known as the Cambrian Explosion, to just 10 Million years or so. These extraordinary fossil deposits, where organisms are so well preserved that even their soft parts remain as carbon films, are referred to as Lagerstätten, a German word that means "resting places", only recently borrowed by geologists. A lagerstatte is a spectacular rarity, and a few dozen of them are scattered through the Earth's geologic record like gems. | |
Figure 01e Chengjiang Fossils [view large image] |
mutation and natural selection together make evolution. But there are other causes for evolutionary change. Darwin himself strongly emphasized the multifactorial nature of evolutionary change and warned against too exclusive a reliance on natural selection. Close examination of the history of life shows that the change is not necessarily progressive; it is certainly not predictable. The earth's creatures have evolved through a series of contingent and fortuitous events such as the Cambrian explosion and the mass extinctions, which imparts a quirky and unpredictable character to life's evolutionary pathway. There is still much controversy over the significance of the Burgess and Chengjiang fossils. What is certain is that the transformation of life from single-celled organisms to multicellular organisms was swift, sudden and widespread. Another significant point is that if evolution was occurring at such a rapid rate, why are the Chengjiang fossils and the Burgess fossils so similar? During the 20 million year period between the two sites, evolution seems to have produced very little change. It seems that all of the diversity that was going to occur happened in a time period as short as 10 million years. Hardly an observation that supports a Darwinian view that life evolved by the slow accumulation of fortuitous mutations. Thus, there is suggestion that complex life came to earth (in the early Cambrian and probably Vendian) from elsewhere with many if not all of the biochemical processes in place. A possible fault with this kind of argument is the strong DNA linkage between the unicellular and mulitcellular organisms. It is highly improbable that the DNA structures of these organims are so closely related if the seed for multicellular organisms has another place of origin. | |
Figure 01f Natural Selection |
Research in 2004 attributed the complexity of multicellular organism to the use of RNA based regulatory signals. The Cambrian explosion was related to the abrupt addition of this genetic regulatory system. Figure 01g shows the complexity of eubacteria and archaea at low levels over the past billion years up to the present. While the complexity in eukeayote organisms advanced graudully up to a ceiling and then increased abruptly at the Cambrian explosion when a new regulatory system became available. (click here for detail). The proliferation of complex life forms some 20 million years prior to the Cambrian explosion might be just the initial trials to become multicellular. | |
Figure 01g Cambrian Explosion [view large image] |
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Figure 01h Cambrian Oxygen Level |
It is reported in 2009 that rather than evolving during the Ediacaran period, the first multicellular animals evolved as early as 850 million years ago (Figure 01i), but remained on the fringes of life until ice ages changed the environment to be more favourable for them. | |
Figure 01i Rise of Animals [view large image] |