Is known as a major unsolved crimes on paleontology and geology ─ ─ Cambrian explosion of life, since Darwin's theory of evolution has been plagued etc. academia. About 600 million years ago, at the beginning called Cambrian geology, the vast majority of invertebrates doors hundreds of years there has been a very short time. This is almost "simultaneously", the "sudden" Cambrian strata appear in numerous categories of invertebrate fossils (arthropods, mollusks, brachiopods and annelids, etc.), but before the Cambrian more ancient formation of a long time but can not find the phenomenon of animal fossils, paleontologists were called "Cambrian explosion", referred to as "the Cambrian outbreak." Darwin noted this fact in his "Origin of Species" writings, and great sense of confusion. He believes that this fact will be used as opposed to strong evidence of its evolution. But he also explained that the Cambrian animals must come from the Precambrian ancestors of animals, is the result of a very long evolutionary process produces; Cambrian animal fossils appear "sudden" and Precambrian animals lack of fossils, the geological record is incomplete due or because the old formations submerged in the ocean's sake.
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Cambrian explosion of life's origins - Ediacaran fauna
寒武纪生命大爆发的起源—埃迪卡拉动物群
寒武纪生命大爆发的起源—埃迪卡拉动物群
Ediacaran (ediacaran) fauna is sprigg in 1947 in Australia's south-central region Pound ediacara first discovered in sandstone layers. Initially it was unable to determine the age of the fauna, was finally identified as the Precambrian age of 6.7 billion years. Ediacaran fauna consists of three doors, 19 genera and 24 kinds of lower invertebrates. Three doors are: coelenterate door, Annelida and Arthropoda. There are nine kinds of jellyfish 7; Hydrozoa 3 3 species; sea gill head (Coral Gang) 3 3 species; Jellyfish 2 are two kinds; polychaete worm two rings are five kinds; 2 are two kinds of arthropods . Multi saved as impression fossils, although their morphology, structure is very primitive, but they are considered one of the most important paleontological discoveries of the 20th century. The findings of the scientific community has long been considered abandoned unlikely before the Cambrian metazoan fossils traditional values. The so-called relative protozoa metazoan entails various multicellular animals Eddie Carla fauna includes a variety of forms peculiar fossils: a huge, flat body, mostly oval or strip-shaped, with a smooth, organic film, is that people ever discovered the oldest and most primitive fossils, but also Archean strata found in the most convincing biological evidence. Press seilacher view Addison karaoke radial growth can be divided into groups of animals, the growth of the bipolar and unipolar three types of growth. In addition to the type of radial growth may have a relationship with coelenterate groups, the emergence of the other two types and categories of non-biological parents after the Cambrian source relationships. Although on the nature Eddie Carla (type) fauna there are many controversial, but its strange shape to many scholars believe that Eddie Carla (type) fauna is the first adaptive radiation of metazoan after they take Unlike most modern body structure changes in the way animals taken. Without increasing the complexity of the internal structure of the body to change only the basic form, it becomes extremely thin, or a pancake shaped strip, the body is sufficiently close to the respective parts of the outer surface, in respiratory and nutrition situation without internal organs. Modern large animals such as parasitic worms Di Most animals take is modern while maintaining the external morphology of round or spherical, the evolution of complex internal organs to expand the corresponding surface area (such as the lungs, digestive tract), can be seen from the fossils, These organisms already has a highly differentiated tissues and organs, indicating that they had not the most primitive type. They represent the emergence of metazoan evolution after the first radiation can therefore be considered Eddie Kara (type) fauna in the late Proterozoic lower oxygen content in large-scale atmospheric conditions metazoan shallow attempt occupation, the results failed, which led to extinction. In the later evolution of metazoan took the second approach, the complexity of the internal organs and species diversity of development, namely the evolution of biological systems.
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Representatives of the Cambrian explosion of life ─ Yunnan Chengjiang fauna
Cambrian typical outbreak is known as one of the most amazing scientific discoveries of the 20th century, China's Yunnan Chengjiang fauna, which is currently the world discovered the oldest and best preserved shelled metazoan groups. The fauna is our young paleontologist Hou Xianguang 1984 in Chengjiang County, Yunnan Maotianshan first discovered. This is a very rich, very perfect preservation, dating back some 570 million years of fossil group, whose members include jellyfish-like creatures, trilobites, a non-appendage arthropods clover, gold arm insects, animals Demodex , sponges, anal animals, annelids, brachiopods no twist Gang, soft tongue snails, speak up bone classes, and algae, and even lower chordates belong or Hemichordata (such as the famous Yunnan insects), etc. . Due to the soft tissue of many animals preserved for study of early material provides excellent invertebrate morphology, lifestyle, environment, etc., but also to explore the planet has become a large shell metazoan outbreaks important window.
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Yunnan Chengjiang fauna significance in the study of biological evolution
Found in Yunnan Chengjiang fauna, making us late Precambrian to Early Cambrian evolutionary development of life have a more clear understanding. Its significance in biological evolution can be summarized as at least two points: First, the discovery of the fauna, once again confirmed the existence of "explosion of life", a "Cambrian explosion" an important pillar theory. Meanwhile, it is the late Precambrian before contacting an important part of the life of early Cambrian evolutionary process. Within this fauna to be found before this century have had two exciting paleontological discoveries. One was discovered in 1910 in North America about 530 million years ago, the Cambrian "Burgess fauna", another is "Egypt dating back 680 million ~ 600 million years between 1947 found in southern Australia Di Kala fauna. " Contact Yunnan Chengjiang fauna became an important part of the Burgess fauna and between the Ediacaran fauna, along with research on the Chengjiang fauna depth Ediacaran - 3 between the Burgess fauna - Chengjiang evolutionary relationships will be more clear. Second, find the Chengjiang fauna as "punctuated equilibrium" theory provides a new basis in fact, impact of Darwin's theory of evolution again. "Punctuated equilibrium" theory that biological evolution like Darwin and neo-Darwinism as highlighted by a slow continuous gradual accumulation process, but long-term stability (even constant) upheaval alternating with short process, thus leaving many vacancies in the geological record. Chengjiang fauna found in the description of biological evolution is not always gradual, but progressive leap coexist with the process.
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To investigate the reasons for the Cambrian explosion of life
Cambrian outbreak attracted numerous paleontologist and evolutionist to find evidence to investigate the cause. 100 years since the evidence produced to explain the two basic viewpoints Cambrian outbreak. One view is that the outbreak of the Cambrian is an illusion, it is the view of some of Darwin or new Darfur activists held. Because evolution is gradual, so-called "explosion" just shows first discovered early Precambrian has been widespread and development of biological organisms in the fossil record, the other fossil groups may be due to incomplete geological record "missing files" for this reason "missing files" is Precambrian experiencing heat and pressure, where fossils have been destroyed. The discovery of a large number of bacteria and cyanobacteria like such a simple prokaryotes exist Precambrian fossils in sedimentary layers, so this explanation is no longer convincing. Another view is that the outbreak of the Cambrian evolutionary process represents a real event, scientists from the changes in the physical environment and the ecological environment are two aspects to explain this phenomenon. In 1965, two American physicists proposed Cambrian outbreak is due to the level of oxygen in the Earth's atmosphere caused by physical factors. They believe that the early Earth's atmosphere contains little or no free oxygen, oxygen is a product of photosynthesis Precambrian and gradually accumulate algae formation. Metazoan requires large amounts of oxygen, while for respiration, on the other hand also in the form of an oxygen absorbing large quantities of ozone in the atmosphere of harmful UV rays, so metazoan harmful radiation from damage. Biologists from the ecological relationships of biological itself to explore this issue, because the evidence of geology negate the views of this oxygen theory. About oxidized rock contains a lot of serious dating back between 1 billion to 2 billion years of extensive sedimentary layers, suggesting that in this period of life erupted enough oxygen conditions already exist. Thus there are two important events from biologists to explore the reasons for the outbreak caused the Cambrian, namely the generation of sexual reproduction and biological reaper appears. From the fossil record, the eukaryotic algae appeared about 900 million years ago, the sexual reproduction, in fact, sexual reproduction occurs earlier. Sexual reproduction occurs throughout the evolution of the biosphere has an extremely important role, because sexual reproduction provides genetic variability, which may further increase the biological diversity, which is one of the reasons for the outbreak caused by Cambrian . Reaper is a biological hypothesis put forward by the American ecologist Stanley, is an ecological theory to explain the outbreak of the Cambrian, that harvest principle. Stanley believes that the 2.5 billion years of Precambrian most of the time, the ocean is an ecosystem in such a simple prokaryotic cyanobacteria composed of primary producers. Communities within the system belong to a single constant in community ecology, the trophic level is simple unique. Due to the physical space is small, but large quantities of this kind biomes occupy tenaciously, so very slow evolution of this community, there has never been a rich diversity. Cambrian outbreak is critical herbivorous Reaper emergence and evolution, namely edible prokaryotes (cyanobacteria) the emergence and evolution of protozoa. Reaper is a greater diversity of producers manufacturing space, and increase the diversity of this producer has led to more specific reaper evolution. Trophic pyramid rapid development in two directions: the producer level than at the end adds many new species, a rich diversity of species at the top and added a new "Reaper" to enrich the nutritional level of diversity. So that the entire ecosystem biodiversity continue to enrich, eventually led to the generation of the Cambrian explosion of life. For the "harvest theory" Scientists have not yet found direct evidence to prove its validity, however, some indirect evidence to support this theory. One indirect evidence from Precambrian stromatolites, these stromatolites composed of algae save the most abundant producers Precambrian community. Today, only rich in stromatolites lack metazoan Reaper barren environments, such as ultra-salt lagoons in. Algae Cambrian formations abound in front, probably reflected the reaper poor. In addition, the ecology field studies have provided some indirect evidence, research shows that in an artificial pond, into predatory fish, will increase the diversity of plankton; remove algae, sea urchins from diverse communities, will make a algae dominated communities and diversity in the fall. Cambrian broke out as the second largest in the history of unsolved land has been concern for people. With the discovery of fossils and build new theory, this mystery will eventually be revealed to the world.
