Cambrian Explosion

It is known as a major unsolved case in paleontology and geology - the Cambrian life outbreak has been plaguing academic circles such as evolution since Darwin. About 600 million years ago, the beginning of the Cambrian period was called the Cambrian period, and most of the invertebrates appeared in a short period of millions of years. This kind of invertebrate fossils (arthropods, mollusks, brachiopods and annechos, etc.) that appeared almost "at the same time" in the Cambrian strata, and the appearance of animal fossils was not found in the older strata before the Cambrian period.

Elephants are called "Cambrian Life Explosion" by paleontologists, referred to as "Cambrian Eruption". Darwin mentioned this fact in his book "Origin of Species" and was very confused. He believed that this fact would be used as strong evidence against its theory of evolution. But he also explained that the ancestors of Cambrian animals must have come from Precambrian animals and were produced after a long period of evolution; the "suddenness" of Cambrian animal fossils and the lack of Precambrian animal fossils are due to incomplete geological records or the submergedness of old strata in the ocean.

Detailed description

In a geological history period called the Cambrian about 530 million years ago, various animals suddenly emerged on the earth. They all originated rapidly and appeared immediately. Arthropods, brachiopods, creepings, sponges, chords and other series of animals with basically the same shape as modern animals made a "collective appearance" on the earth, forming a prosperous scene where multiple species of animals exist at the same time. This is the "Cambrian Life Breaking Out" which is still listed by the international academic community as one of the "Top Ten Scientific Problems". According to traditional and classic biological theory, Darwin's biological evolution believes that biological evolution has undergone a long evolution process from aquatic to land, from simple to complex, from low to high. This process is gradually realized through the slow rolling of the two wheels of natural selection and genetic variation. Chinese scientists challenged this authoritative theory through the research of ancient fossils.

The fossils of the "Chengjiang Fauna", which is internationally known as "one of the most amazing discoveries of the 20th century", opened a precious scientific window for exploring the mystery of the "Cambrian Life Explosion". On July 1, 1984, the "Chengjiang Fauna" was first discovered in Chengjiang County, Yunnan Province. This fossil group of multiple animals has many types and has preserved animal soft structures very rare. For the first time, it vividly reproduced the magnificent landscape of ancient marine life and the original characteristics of the present animals, and provided direct evidence for the study of the "Cambrian Eruption" with rich biological information.

After years of hard work, China has achieved a leading international position in paleontology research on the "Cambrian Eruption". Not long ago, the "Chengjiang Eruption and Cambrian Eruption" project, led by Professor Hou Xianguang of Yunnan University and Professor Shu Degan of Northwest University, won the first prize of the National Natural Science Award for making major breakthroughs in the early life evolution research.

The ancient fossil groups miraculously preserved the mineralized bones of organisms and also preserved a large number of soft tissue marks, such as epidermis, sensory organs, cilia, eyes, intestines, stomach, digestive glands, oral and nerves. Some animals even seemed to have a full meal before they died, and the food in the digestive tract was still recognizable. Fossils Chinese scientists' continuous excavation and discovery of the "Chengjiang fauna" and in-depth systematic research have explored the origins of animals such as vertebrates, arthropods, chelifs and crusts, and confirmed the vividness.

The phylum and subphylum and complex ecological systems originated in the early Cambrian period, challenging the bottom-up inverted cone evolution theoretical model, providing fossil evidence for the top-down explosive theoretical model. The Chengjiang fauna group has been described in total, belonging to more than 120 species, including sponges, coelenterics, gill animals, leaf pods, brachiopods, mollusks, arthropods, echinoderms, chords, as well as some strange groups with unknown classification locations. In addition, there are many symbiotic seaweeds.

Through researching rich fossil information, scientists have proposed various hypotheses to reveal the mystery of the "Cambrian explosion". Researcher Chen Junyuan proposed the idea that Cambrian biological mutations have extremely obvious spontaneous evolutionary behaviors; Professor Shu Degan proposed the hypothesis that "the two paleobiological geographical divisions of warm water and cold water in the Cambrian era" are also in line with. However, there is no clear, conclusive and convincing explanation at present. Scientists are also continuing to devote themselves to field investigations and research in order to completely solve the mystery of the "Cambrian explosion" as soon as possible.

origin

The Origin of the Cambrian Life Explosion—Edicara Fauna

The trilobite Ediacaran fauna was first discovered by Sprigg in 1947 in the Pond sandstone formation in the Ediacara region of southern central Australia. At first, people failed to determine the age of this fauna, and was finally determined as the Precambrian, with an age of 670 million years. The Ediacaran fauna consists of three phyla, 19 genera, and 24 lower invertebrates. The three phylas are: Coelenteria, the Antarctica and the Arthropod. Jellyfish have 7 genera and 9 species.

;There are 3 genera and 3 species of the Aquatica;There are 3 genera and 3 species of the Aquatica (Coricus);2 genus and 2 species of the Jellyfish;2 genus and 5 species of the polyhedral worm;2 genus and 2 species of arthropods. Most of them are preserved as imprint fossils. Although their shape and structure are primitive, they are considered to be one of the most important paleontology discoveries in the 20th century. This discovery has caused the scientific community to abandon the long-standing traditional concept that metazoan fossils could not appear before the Cambrian period. The so-called metazoan refers to various multicellular animals relative to protozoans.

The Edicara fauna contains many unique animal fossils: their bodies are huge and flat, mostly oval or striped, with smooth organic matter membranes. They are the oldest and most primitive fossils discovered so far, and are also the most convincing biological evidence found in ancient strata. According to Seilacher's point of view, the Edicara fauna can be divided into three types: radial growth, polar growth and monopolar growth. Except for the types of radial growth that may have groups related to coelenteric animals, the other two categories have no relative relationship with the biological phyla that appeared after the Cambrian period.

Although there are many controversies about the nature of the Edhikara fauna, its strange shape has led many scholars to believe that the Edhikara fauna is the first time that metazoans have adapted to radiation. They adopt different forms of the body structure adopted by most modern animals. They do not increase the complexity of the internal structure, but only change the basic shape of the body, become very thin, into strips or pancakes, so that the parts of the body are fully close to the outer surface, and breathe and ingest nutrition without internal organs. For example, modern large parasites, most modern animals adopt the external shape that maintains a round or spherical shape while maintaining the outer shape.

Complex internal organs have evolved to expand the corresponding surface area (such as lungs and digestive tracts). From the fossils, it can be seen that these organisms have highly differentiated tissues and organs, which means that they are no longer the most primitive types. They represent the first radiation evolution after the emergence of metazoans. Therefore, it can be considered that the Edhikara (type) animal group was an attempt by metazoans to occupy shallow seas on a large scale under the conditions of low atmospheric oxygen content in the late Proterozoic period, which failed and led to extinction. In the subsequent evolution process, metazoans adopted the second method to complicate internal organs and develop diversified species, that is, biological system evolution.

represent

introduce

Representative of the Cambrian life explosion--Yunnan Chengjiang Animal Group

The typical representative of the Cambrian outbreak in the museum is the Chengjiang fauna in Yunnan, my country, known as one of the most amazing scientific discoveries in the 20th century. It is the oldest and most fully preserved mesozoic group discovered in the world. This group was first discovered by the young paleontologist Hou Xianguang in Maotian Mountain, Chengjiang County, Yunnan Province in 1984. This is a fossil group with rich content and perfect preservation, about 570 million years ago. Its members include jellyfish-like organisms, trilobites, and non-triple-like appendages.

Leaf arthropods, golden-armed insects, demotile animals, sponges, intraanal animals, anterior animals, strandless brachiopods, soft tongue snails, caudal bones, and algae, and even lower chords or semicords (such as the famous Yunnan insect). Because the soft tissues of many animals are well preserved, it provides excellent materials for studying the morphological structure, lifestyle, ecological environment of early invertebrates, and also becomes an important window for exploring the outbreak of large-shelled epizoa on the earth.

significance

Significance of the Chengjiang fauna in Yunnan in biological evolution research

The discovery of the Chengjiang fauna in Yunnan has given us a clearer understanding of the evolution and development of life from the late Precambrian to the early Cambrian period. Its significance in biological evolution can be summarized in at least two points:

First, the discovery of this fauna once again confirmed the existence of the "big explosion of life" and became an important pillar of the "cambrian explosion" theory. At the same time, it is also an important link in the evolution of life from the late Precambrian to the early Cambrian period.

There were two exciting paleontological discoveries in this century before the group was discovered. One was the "Burgis fauna" discovered in North America in 1910 in 1910, and the other was the "Edicara fauna" between 680 million and 600 million years ago, found in southern Australia in 1947. The Chengjiang fauna in Yunnan has become an important link between the Burgis fauna and the Edicara fauna. With the deepening of research on the Chengjiang fauna, the evolutionary relationship between the three Edicara-Chengjiang-Burgis fauna will be clearer.

Secondly, the discovery of Chengjiang fauna provides a new factual basis for the "intermittent balance" theory and has another impact on Darwin's theory of evolution. The "intermittent balance" theory believes that the evolution of organisms is not a slow continuous gradual accumulation process as emphasized by Darwin and neo-Darwinists, but a process of long-term stability (or even unchanged) alternating with short-term drastic changes, leaving many vacant in the geological record. The discovery of Chengjiang fauna shows that the evolution of organisms is not always gradual, but a process of coexistence of gradual and leap forward.

Discussion on the reasons

The Cambrian outbreak attracted countless paleontologists and evolutionists to find evidence to explore its cause. The evidence over the past 100 years has produced two basic views that explain the Cambrian outbreak. One view believes that the Cambrian outbreak is an illusion, which is the view held by some Darwinian or NeoDalists. Since evolution is gradual, the so-called "explosion" only shows that the first time a creature that had been widely present and developed in the Precambrian record was discovered in the biological fossil record, while other biological fossil groups were

The reason for this "failure" may be due to incomplete geological records is that the Precambrian strata experiences heat and pressure, and the fossils in it are destroyed. Since it is discovered that there are a large number of prokaryotes such as bacteria and cyanobacteria in the Precambrian fossil sedimentary layer, this explanation is no longer convincing. Another view is that the Cambrian outbreak represents a real event in the process of biological evolution, and scientists explain this phenomenon from the perspective of changes in the physical environment and ecological environment.

In 1965, two American physicists proposed that the Cambrian outbreak was caused by the physical factor of the oxygen level in the Earth's atmosphere. They believed that in the early Earth's atmosphere, there was little or no free oxygen, and oxygen was the product of photosynthesis of the Precambrian algae plants and gradually accumulated. Metazoans need a large amount of oxygen, which is used for respiration on the one hand, and on the other hand, oxygen absorbs a large amount of harmful ultraviolet rays in the atmosphere in the form of ozone, preventing metazoans from damage from harmful radiation.

Biologists explore this issue from the ecological relationship between organisms themselves, because geological evidence denies the view of this oxygen theory. The extensive sedimentary layer contains a large number of severely oxidized rocks, which shows that there are sufficient oxygen conditions for life outbreaks during this period. Therefore, biologists explore the causes of the Cambrian outbreak from the emergence of two important events, namely the generation of sexual reproduction and the emergence of biological harvesters.

Judging from fossil data, eukaryotic algae had sexual reproduction about 900 million years ago. In fact, sexual reproduction occurred earlier. The occurrence of sexual reproduction plays an extremely important role in the evolution of the entire biological world. Since sexual reproduction provides genetic variability, it is possible to further increase the diversity of organisms, which is one of the reasons for the Cambrian outbreak.

The biological harvester hypothesis was proposed by American ecologist Stanley. It is an ecological theory that explains the Cambrian outbreak, namely the harvesting principle. Stanley believes that for most of the 2.5 billion years of the Precambrian period, the ocean was an ecosystem composed of simple primary producers such as prokaryotic cyanobacteria. The communities in this system are ecologically single and unchanging communities, and the trophic level is also simple and unique. Since physical space is tenaciously occupied by such biological communities with few species but large numbers, the evolution of this community is very slow and has never been rich in diversity. The key to the Cambrian outbreak

It is the emergence and evolution of herbivorous harvesters, namely the emergence and evolution of protozoa that eat prokaryotic cells (cyanobacteria). Reapers create space for producers to have greater diversity, and this increase in producer diversity has led to the evolution of more specific harvesters. The trophic pyramids develop rapidly in two directions: the producers at the bottom level have added many new species, enriched species diversity, and added new "reapers" at the top, enriching the diversity of the trophic level. This has led to the continuous enrichment of the biodiversity of the entire ecosystem, which ultimately led to the .

Scientists have not yet found direct evidence to prove its correctness. However, some indirect evidence supports this theory. One of the indirect evidence comes from the Procambrian stromatolites, which consist of algae, which preserves the richest producer community of the Precambrian. Today, stromatolites are only abundant in barren environments lacking metazoan harvesters, such as saltwater lakes with super salt volume. The large number of algae in the Precambrian strata probably reflects the poverty of the harvesters at that time. In addition, ecological field studies also provide some indirect evidence, which shows that putting predatory fish in an artificial pond will increase the diversity of plankton; removing sea urchins from diverse algae communities will cause a certain algae to dominate the community and its diversity will decrease.
Chapter completed!