I! Deduce The World For Tens Of Billions Of Years

The Cambrian Period (Cambrian) is the beginning of the Phanerozoic Era, about 542 million years ago - 488 million years ago. The name comes from Cambria, an ancient place name in Wales, where the Cambrian strata were first studied. The term Cambrian was first introduced into the geological literature in 1835 by Eagle Country geologist A Sedgwick. It originally refers to all the strata under the old red sandstone of the Devonian. In the era of the mules and horsemen, the North Wales Mountains were once called the Cambrian Mountains, so Sedwick called this period the Cambrian Period. Its duration is measured at 53.7 million years by uranium-lead dating. The Chinese name comes from the transliteration name Cambrian (pronunciation: カンブキ, luomazi: kanbuki) that the natives of the island used to pronounce in Japanese Chinese characters.

The Cambrian can be further divided into Early Cambrian, Middle Cambrian, and Late Cambrian. The Cambrian is the earliest geological era of the Phanerozoic, and the next period is the Ordovician.

In traditional theory it can be divided into three periods: Early Cambrian (541-540 million years ago), Middle Cambrian (541-523 million years ago), and Late Cambrian (523-492 million years ago) ). This is a division based on lithostratigraphy.

In recent years, the Blue Star Stratigraphic Council has established a new chronostratigraphic table of the Cambrian period based on the research of Huayan State scientists.

In traditional lithostratigraphy, the Cambrian is divided into three parts: Early Cambrian, Middle Cambrian and Late Cambrian.

However, according to the new requirements of blue star stratigraphy research, the new chronostratigraphic Cambrian quartering method is used on blue star to replace the third rule, namely:

Newfoundland, Second, Third, Hibiscus.

The Newfoundland system and the second system are each divided into two stages, and the third system and the Furong system are each divided into three stages. Contrary to our general understanding, trilobites, the representative of the Cambrian explosion of life, appeared in the early period of the Second Line, not the beginning of the Cambrian.

The Cambrian fauna is characterized by the appearance of a large number of marine invertebrates with hard shells and numerous categories, which is a great development in the history of biology. Among them, trilobites are the most common and are an important basis for dividing the Cambrian system. In addition, there are brachiopod ligule shells without hinges and chitinous shells, small garden shell shells, ancient cups and soft tongue shells, etc. The flora is dominated by algae, with some micro-archaic plants. The division of trilobite groups in the Cambrian period is particularly obvious.

There are two main zoogeographic regions, namely the eastern Pacific region and the western Atlantic region. Atlantic fauna, whose distribution range includes both sides of the Atlantic Ocean, such as Northwest Europe and the New England area in the easternmost part of the Americas. The Early Cambrian, Middle Cambrian, and Late Cambrian are represented by Helmia, Mirabilis, and Oleopsis, respectively. The Pacific fauna is represented by Laidlici, Kuting and Pleiades.

Cambrian Explosion (Cambrian Explosion): Known as a major unsolved case in paleontology and geology, it has been plaguing evolution and other academic circles since Darwin. About 600 million years ago, at the beginning of what is known in geology as the Cambrian Period, most invertebrates emerged within a short period of a few million years.

This kind of invertebrate fossils (arthropods, molluscs, brachiopods and annelids, etc.) that appeared suddenly and almost simultaneously in the Cambrian strata, and in the older strata before the Cambrian The phenomenon that no animal fossils have been found for a long time is called the Cambrian Explosion of Life by paleontologists, or the Cambrian Explosion for short.

Darwin referred to this fact in his work On the Origin of Species and was baffled. He thought this fact would be used as strong evidence against his theory of evolution. But he also explained that Cambrian animals must have come from the ancestors of Precambrian animals, which were produced after a long evolutionary process; Lack, due to incomplete geological records or due to old formations submerged in the ocean.

The Cambrian is the first period of the Phanerozoic Paleozoic in the division of geological time. It is about 570 million to 510 million years ago. The Cambrian is the beginning stage of modern organisms and the period when modern life on earth began to appear and develop. . The Cambrian period is very distant and unfamiliar to us. The characteristics of the earth's continents during this period are completely different from today's. The Cambrian period is often referred to as the age of trilobites because Cambrian rocks are richer in mineralized trilobite crusts than other groups. In addition, the Cambrian period also produced an important event in the history of evolution, the Cambrian explosion of life. In a very short period of time (very short in the geological sense, in fact, it is also millions of years long), biological species suddenly enriched, increased explosively. It means that in addition to slow gradual changes, biological evolution may also proceed in a jumping manner. At that time, rich and diverse marine invertebrates appeared, and a large number of fossils were preserved, so it was possible to study the status of the biological world at that time, and to use the method of biostratigraphy to divide and compare the strata, and then to study the organic world and the inorganic world. A relatively complete development history of the world. However, the Chengjiang biota tells us that the various animal phyla living on the earth today appeared almost simultaneously shortly after the beginning of the Cambrian period.

The Cambrian period is the beginning of the Phanerozoic Eon, marking a new chapter in the evolution history of the earth's organisms. In just a few million years after the beginning of the Cambrian period, a large number of multicellular organisms suddenly appeared, including the ancestors of almost all groups of living animals. This explosive biological evolution event is called the Cambrian life giant. Explosion (Cambrian explosion). Marine invertebrates with shells and skeletons tend to prosper. They live in the bottom habitat and feed on tiny algae and organic matter particles. Among them, the most prosperous arthropod trilobites, so the Cambrian period is also called trilobites. Insect era, followed by brachiopods, ancient cup animals, echinoderms and gastropods. The biological forms of the Cambrian period are peculiar, which are very different from the creatures we can see on the earth now. The more famous ones are the Chengjiang biota in the south of Caiyun in the Early Cambrian and the Burgess Shale biota in the Middle Cambrian in Canada. The Cambrian biological kingdom was dominated by marine invertebrates and marine algae. Many higher classes of invertebrates such as arthropods, echinoderms, molluscs, brachiopods, graptolites, etc. are represented. Among them, trilobites in the phylum Arthropoda are the most important, followed by brachiopods. In addition, ancient cups, ancient ostracods, soft tongue snails, conodonts, nautilus, etc. are also very important. Aside from conodonts, there are many other representatives of higher chordates, such as Huayan eel, Caiyunzhinan fish, Haikou fish, etc. Pikai worms in the rocks, and duck scale fish in the Cambrian period of Yingjiang Country.

lichen

lichen

In humid lowlands, mosses and lichens may be distributed in lower plants, but they still lack true rhizome tissue, making it difficult to live in dry areas; invertebrates have not yet evolved the ability to adapt to living in the air. There were no real land creatures in the Cambrian, and the continent was lifeless and desolate.

Paleontology uses the term explosion to describe the sudden explosion of biodiversity. According to the sudden diversity and complexity of trace fossils and small shell fossils at the beginning of the Cambrian, the theory of the Cambrian explosion had been proposed before the discovery of the Chengjiang biota, but the theory of the Cambrian explosion and the animals produced by the Cambrian explosion Little is known about the characteristics of the community structure. Even the famous Burgess Shale fauna fossils in Canada are more than 10 million years later than the Cambrian explosion, which cannot answer the specific life in the early Cambrian ocean.

The geological age of the Chengjiang Biota is in the Cambrian Explosion, which allows us to see the true appearance of the fauna 530 million years ago. Various animals originated rapidly during the Cambrian Explosion and appeared immediately. It pushes back the history of animal diversity to the early Cambrian.

The creatures in the Cambrian period were peculiar in form and very different from the living creatures on the earth. The oldest species of fish that also appeared in this era is Haikouichthysercaicunensis, which was found in the Chengjiang biota.

The beginning of the Cambrian period marked that the earth has entered a new stage of biological prosperity. Before the Cambrian period, the earth had already been formed, but it was dead silent in the long process of billions of years. At that time, there were no many types of creatures on the earth. In this way, scientists call the long and lifeless period before the Cambrian the Precambrian. The Precambrian period accounts for about five-sixths of the entire geological history, and we know very little about this period of the earth's history due to insufficient biological evidence.

According to the precious information about signs of life activities, and also for the convenience of research, geologists divided the long Precambrian into two parts: the Archaean and the Proterozoic. Before the Archaic period (the beginning of the earth's formation - 3.8 billion years ago), there were many different names.

The Archaean is far away from us, and its time limit is from about 3.8 billion years to 2.6 billion years ago, as long as 1.2 billion years. Archaean is the initial period with clear historical records. During this long 1.2 billion years, it was the initial period after the formation of the earth. Bald hills and deserts were formed everywhere on the surface. Due to the age, it is indeed difficult to find fossils, and people know very little about the life activities of this period. However, in the second half of the 20th century, scientists successively made significant gains in South Africa and Australia, and found stromatolites in sedimentary rocks that were not too metamorphosed, which is the product of microbial and algae activities. In addition, a large number of organic compounds (such as benzene, hydrocarbon benzene, etc.) and cyclic compounds (such as furan, methanol, acetaldehyde, etc.) have been analyzed in these ancient rock formations. In a set of ancient sedimentary rocks in South Africa, scientists have discovered more than 200 ancient cell fossils that are very similar to prokaryotic algae with the help of advanced precision observation instruments. These microfossils are generally oval in shape and have smooth organic membranes. The oldest and most primitive fossils discovered so far are also the most convincing biological evidence found in Archaean strata. From the perspective of the biological world, this is the initial stage of the emergence of primitive life and biological evolution. At that time, there were only a small number of prokaryotic organisms, and they only left very few fossil records. From the perspective of the non-biological world, the Archean was a period of thin crust, steep geothermal gradient, intense and frequent volcanic-magmatic activities, deformation and metamorphism of rock formations, lack of free oxygen in the atmosphere and hydrosphere, and the formation of a series of special sediments ; It was also a period when the silica-alumina crust formed and continued to grow, and it was also an important mineralization period.

The time limit of Proterozoic is from 2.6 billion years ago to 570 million years. During this period of geological history, prokaryotic organisms evolved into eukaryotic cell organisms, forming the bacteria-algae era of geological history. People have found micro-ancient plant fossils, macro-algae fossils and stromatolites in the ancient strata of this period. In our Huayan country alone, paleontologists have discovered more than 80 genera and nearly 200 species of micro-paleoplant fossils in different periods of the Proterozoic era. Life flourished further in the Proterozoic era, and the earth at that time was no longer barren. . In the early days, some continental plates with wide range, large thickness and relatively stable appeared on the surface. Therefore, in terms of lithospheric structure, the Proterozoic was more stable than the Archaean. The atmosphere in the late Early Proterozoic already contained free oxygen, and with the increasing prosperity of plants and the continuous strengthening of photosynthesis, the oxygen content in the atmosphere continued to increase. The middle and late Proterozoic algal plants were already very prosperous, which was obviously different from that of the Archaean.

The end of the Proterozoic period, from about 850 to 570 million years, was named the Sinian period, because this period of time has the significance of connecting the past and the future in the evolution of life, and it was named in the Huayan Kingdom.

Sinian means the country of Huayan, and the ancient India called Huayan land Sinian. German geologists first used it in stratigraphy, and later many scholars followed suit, but with different meanings. Later, geologists redefined the Sinian period. Li Siguang, a famous geologist in Huayan State, and others established a complete Sinian geological section in the Three Gorges of the Yangtze River. This is the famous Xiadong section, which provides stratigraphic correlation to the world. basis.

There has been clear biological evidence for the Sinian period. In the animal kingdom, there appeared low-level small hard-shelled species and a large number of naked high-level animals. The latter is the Ediacaran fauna found in Australia. In terms of plants, it is manifested as the further prosperity of advanced algae (such as red algae, brown algae, etc.), and the rapid development of macro algae. At this time, the earth has completely changed its lifeless and lifeless appearance.

Distant Ancestors of Insects----Fuxian Lake Insect Ecological Landscape

Distant Ancestors of Insects----Fuxian Lake Insect Ecological Landscape

The Sinian period is a unique period of geological history in the last Proterozoic period. From the perspective of biological evolution, the Sinian has an important difference from the Proterozoic, which does not contain reliable animal fossils, because it contains metazoan fossils without hard shells; but compared with the Cambrian, which is rich in animal fossils with shells , the fossils contained in the Sinian system are not only monotonous in type, small in number and very limited in distribution. Therefore, effective biostratigraphic work cannot be performed using the animal fossils therein. The most prominent feature of the Sinian biosphere is the emergence of many types of metazoans without hard shells in the later period, and a small number of small animals with shells in the late period. Higher algae prospered further, some new types of microscopic ancient plants appeared, and stromatolites tended to flourish in the early Sinian period, but the number and types suddenly declined in the later period. From the perspective of the structure of the lithosphere, several large and relatively stable continental plates appeared on the surface during the Sinian period, on which there were already typical caprock deposits, similar to the Paleozoic. Therefore, the Sinian can be considered a transitional period between the Proterozoic and Paleozoic.

The Ediacaran fauna is mainly composed of creatures similar to jellyfish, worms, and Seabranches, and they are mostly preserved as imprinted fossils. Although their shape and structure are very primitive, they are considered to be the most important palaeontology in the 20th century. One of the discoveries. This discovery made the scientific community abandon the long-standing traditional concept that it was impossible to appear fossils of metazoans before the Cambrian. The so-called metazoa refers to various multicellular animals relative to protozoa.

The Ordovician Period (Ordovician Period, Ordovician, symbol O), the name of the geological age, is the second period of the Paleozoic Era (the emergence of primitive vertebrates), which began 500 million years ago and lasted 65 million years. The Ordovician began at an isotopic age of 488.3±1.7Ma (Million Anniversary, million years,) and ended at 443.7±1.5Ma.

In terms of geology, the Ordovician is the period from 510 million to 438 million years ago in the Paleozoic Era. It can be divided into three periods-the early Ordovician (early Ordovician, 510 million to 478 million years ago) , Middle Ordovician (Middle Ordovician, 478 million years to 453 million years ago) and Late Ordovician (Late Ordovician, 453 million years to 438 million years ago).

The Ordovician was one of the most extensive periods of transgression in history, and marine strata were widely distributed in many parts of the world. In the platform area inside the plate, sea water is widely distributed, showing the general development of littoral neritic carbonate rocks, and in the active trough area at the edge of the plate, it is a relatively deep water environment, forming thick neritic and deep marine clastic deposits and volcanic eruptions. A large-scale ice age occurred at the end of the Ordovician, and its distribution included Africa (especially North Africa), Argentina and Bolivia in South America, Spain and southern France in Europe.

The Ordovician is an era in the history of the earth when the continents suffered extensive transgression, an era of intense volcanic activity and crustal movement, and an era of climate differentiation and the development of glaciers. The Ordovician was the period when marine invertebrates really flourished, and it was also the period when these organisms experienced obvious ecological differentiation. In the late Ordovician period, important tectonic changes, magmatic activities, and thermal metamorphism occurred in many areas of the continents, causing some areas of these active areas to fold into mountain systems, thus changing the crustal structure and paleogeographical outline to a certain extent.

Scientists believe that during the Ordovician period, the positions of the continents relative to the poles and the relative positions between the continents have undergone important changes. At that time, central and northern Siberia, parts of northern Canada, northern Huayan, and central and western Australia were all regions with hot and dry climates; on the contrary, the Sahara Desert in North Africa and the Cape region in South Africa were once covered with thick ice. , belonging to the cold climate area. This shows that during the Ordovician period, the ancient Antarctic was south of the current Sahara Desert, the ancient North Pole was located in the South Pacific Ocean, and the ancient equator happened to pass through central and western Siberia and Central Asia, passing through western Canada and heading south to the South Pacific coast.

Huayan Kingdom's transgression continued in the sea area. The Yangtze Platform and the western edge of the Zhongchao Platform rose slightly in the Middle and Late Cambrian or Early Ordovician, the early Ordovician strata were missing, and the newer Ordovician strata were in pseudo-integrated contact with the Cambrian. In the central and eastern parts of the Sino-Korea platform and the Yangtze platform, the Ordovician strata and the Cambrian strata are in integrated contact. After the Middle Ordovician, the Sino-Korea platform rose to land, and there was no sedimentation in the Late Ordovician except for the western edge. The Ordovician Caledonian movement manifested as frequent oscillating movements in the platform area, and there were more volcanic eruptive rocks, intermediate-basic and intermediate-acid volcanic rocks in the geosyncline area, such as the northern geosyncline area. There are two periods of volcanic activity in the Qilian Mountains trough, one is the middle Early Ordovician and the other is the Late Ordovician.

There are four stable platform regions on the Eurasian continent, namely the Maoxiongguo platform (Eastern European platform), the Siberian platform, and the smaller Sino-Korean platform and the Yangtze platform. The Indian peninsula and the Arabian peninsula are also stable areas, but they are also included in the range of the southern continent. The aforementioned four platforms, except for a few areas, are basically intruded by seawater, forming shallow sea waters, and the surroundings of the platforms are surrounded by geosynclines. On the southern edge of the Maoxiongguo Platform and the Yangtze Platform, the sea area in an east-west strip is the ancient Mediterranean Sea. The southern edge of the ancient Mediterranean ended in northern Africa, the central part of the Arabian Peninsula, the southern part of Ilang, and the northern part of the Indian peninsula. It connected to the eastern part of Australia and the northern Ordovician sea area through the Indochina Peninsula to the south, and may extend to the Antarctic region in the south. Most of North America is platform neritic area, and the deposits are mainly quartz sandstone, shale and carbonate rock, and the thickness is not large. The east and west sides of the North American continent are sea areas of the geosyncline, the west is dominated by clastic rocks and carbonate rocks, and the east is dominated by hard sandstone, mudstone and volcanic rocks. The western Pacific coast of South America is a trough sea, and the central part of the north is a platform shallow sea. The surrounding margins of the southern continent are surrounded by geosynclines or platform-type seas, and Africa, the Indian peninsula, southwestern Australia, eastern South America, and eastern Antarctica are all land.

The early and middle Ordovician inherited the climate of the Cambrian, with a warm climate and extensive transgression; in the late Ordovician, large-scale continental ice sheets and ice sea deposits occurred in the western part of the southern continent, representing a cold polar climate. According to paleomagnetic data, the Ordovician South Pole should be located in the northwest of North Africa today, which is consistent with the explanation that the distribution of African moraine layers should be located in the Antarctic Circle. The eastern part of the southern continent is still near the equator. There are evaporite deposits in North America, Siberia, and North China of Huayan Kingdom, which are presumed to be dry and hot climate environments and belong to low latitude areas. The Ordovician North Pole should be located in the South Pacific, and the continental region was basically located in the Southern Hemisphere. Judging from the sediments, the climate zoning of the Southern Hemisphere was relatively obvious at that time. Due to the existence of the large ice age at the end of the Late Ordovician, it also affected the decline of global sea level and caused extensive sea retreat.

During the Ordovician period, the climate was mild and shallow seas were widely distributed. Many parts of the world (including most of China) were covered by shallow seawater. Marine organisms developed unprecedentedly and were more prosperous than those in the Cambrian period. Fossils are most common in trilobites, graptolites, brachiopods, Cystoids in echinoderms, and Nautilites in molluscs, and among bryozoans, conodonts, and coelenterates There are also many corals, crinoids in echinoderms, ostracods and bryozoans in arthropods. Eutypterids in arthropods and jawless vertebrates (such as Os-tracoderms) in vertebrates have all appeared. Lower marine plants continued to develop, and freshwater plants are speculated to have appeared in the Ordovician.

freshwater jawless fish

During the Early Ordovician, about 500 million years ago, the first reliable terrestrial vertebrates appeared - freshwater jawless fishes.

In the middle of the Ordovician, the primitive vertebrate fishes - star turtles and pleated fishes - appeared in the Rocky Mountains of North America, and also appeared in Australia in the southern hemisphere. Plants are still dominated by marine algae.

During this period, brachiopods evolved rapidly, and most of the groups had appeared. Brachiopods with hingeless and chitinous shells gradually declined, while hinged shells with calcareous shells flourished for a while; nautiluses entered a prosperous period. , their huge bodies were ferocious carnivorous animals in the Ordovician ocean; due to the appearance of a large number of carnivorous nautiluses, in order to defend themselves, trilobites grew many needles on the chest and tail to avoid predators' attacks or devour. Corals began to appear in the Ordovician, and although complex corals were relatively primitive, they were able to form small reefs. The stromatolites, which flourished during the Precambrian period, declined sharply during the Ordovician period due to the great development of marine invertebrates.

Sea creatures of the Ordovician period were the earliest ancestors of modern animals. Corals and ancient starfish called asteroids grow on the ocean floor. Shelled animals on the seafloor include molluscs related to modern oysters, mollusc-looking brachiopods, and gastropods with curled shells. Cephalopods -- cousins ​​of the living squid -- swim swiftly across the ocean floor in search of prey. But the biggest newcomers were jawless ones like the sacabamba fish. Jawless species, such as the sacabamba fish found in South America, were among the earliest vertebrates on Earth. There were still no animal species living on land during this period.

The Silurian Period (the era of graptolite, when terrestrial plants and jawed animals appeared) is the last period of the Early Paleozoic Era and the third period of the Paleozoic Era. It began about 440 million years ago and ended about 410 million years ago. Transliteration by Shimamoto scholars (Silu in Japanese is pronounced as siru, and the sound is close to Silu), and it is borrowed from Chinese. Because the Silurian system was well developed on Gotland Island in the Baltic Sea, it was once called the Gotlandian system. The Silurian can be divided into early, middle and late three generations.

The name Silurian comes from the Silures, an ancient tribe in Wales. In 1835, R.I. Morrison of the Eagle Kingdom established the generalized Silurian system in Wales, divided the rock series, and compared them with graptolite and crustal fossils. In 1879, C. Lapworth named the lower layer of Morrison's generalized Silurian system as the Ordovician system. The Chinese name comes from the transliteration name Siluruki (pronunciation: シルキ狐马字: siruki) that the natives of the island used to pronounce in Japanese Chinese characters in the old days.

liter, showing a huge transgressive cycle. In the late Silurian period, the crustal movement was strong, the paleo-Atlantic closed, some plates collided, and some geosyncline folds rose, the paleogeography changed dramatically, the continental area expanded significantly, and the biological world also underwent a huge evolution. The history of the earth's crust has developed into a turning point.

Silurian strata are widely distributed in the world, and shallow marine deposits are deposited in most parts of Asia, Europe, America, and parts of Australia. Most of Africa and Antarctica are land.

In the Silurian stratification system, graptolite is the preferred category, and Landovelli, Wenlock, and Rodlow are all established in Eagle Country. In addition, there are well-developed Silurian strata and biota in southern Norway, Anticosti Island in eastern Canada, Gotland in Sweden, Podolia in Ukraine, and Prague in the Czech Republic and Slovakia. .

For the top boundary of the Silurian, the bottom of the Monoraptus uniformis biological zone has been selected as the boundary, and the Kroenke section in the Balland area of ​​Czech Republic and Slovakia has been selected as its boundary stratotype section. The bottom boundary of the Silurian system is bounded by the bottom boundary of the Parakidoraptus acuminatus belt, and the stratotype of the boundary line is selected from the Dobs Linn section in the Murfa area of ​​Scotland. Due to the complicated geological structure, single lithofacies and monotonous fossils of this section, the depositional environment is not suitable for benthic organisms, so this plan has yet to be tested.

Silurian invertebrates are closely related to Ordovician organisms, and many species have entered a new stage of recovery after experiencing the end-Ordovician extinction event.

Graptolite is an eye-catching organism in the marine floating ecological domain. Graptolite is mainly composed of single graptolite, such as single graptolite, bow graptolite, saw graptolite, raking graptolite and so on. Graptolite is widely distributed and evolves rapidly, so it has unique value in stratigraphic correlation.

Among the shallow sea-dwelling organisms, brachiopods are the most abundant. The shell length can exceed 80 cm, and the development of the spoon-shaped platform and the Wufang shell family is the most characteristic category, which began in the Late Ordovician and reached its peak in the Silurian. The Wudongbei, Wuhuangbei, and Shiyan tribes have developed steadily since the Ordovician, and later became the main groups of brachiopods. Ordovician shellfish and crescent shellfish, which proliferated in large quantities in the Ordovician, declined significantly in the Silurian Period.

Corals and layer foraminifera are also more prosperous, often forming reefs, biomounds, and biolayers. Radiant corals, bed corals, and solar corals are often found in the sea since the late Landofresch, and there are many types of them. These types of corals and layer foramen reached their peak in the Devonian, but they have long been extinct.

Compared with the Ordovician, the biological features of the Silurian period had further development and changes. Marine invertebrates still played an important role in the Silurian, but the species replacement and internal components of each taxa changed. For example, the graptolites retained the double-graptolites, and the newly emerging monograptolites were also very prosperous; the internal structure of the brachiopods became more complicated, such as the five-chambered shellfish, the stone swallow shellfish, and the small-mouth shellfish were developed; the molluscs Among animals, cephalopods and nautilus decreased significantly, while bivalves and gastropods gradually developed; trilobites began to decline, but arachnids and ostracods developed in large numbers; It is said that sea scorpions were widely distributed in the late Silurian ocean; corals further flourished; echinoderms of sea forests were greatly reduced, and crinoids appeared in large numbers in Silurian.

Among vertebrates, jawless species developed further, and jawed placoderms and spiny fishes appeared. This was a major event in the evolution of vertebrates. Fishes began to conquer waters, creating a great development for Devonian fishes. conditions.

In terms of plants, except that marine algae were still flourishing, at the end of the Late Silurian

, the bare fern among terrestrial plants appeared for the first time, and plants finally began to develop from water to land. This is another major event in biological evolution.

The subdivision of the Silurian system, including 4 systems and their respective divisions.

①Landovelli system. The standard area is around the town of Llandovery in Darfed, South Wales, Eagle Country. The Landovelli system is divided into 3 stages, the bottom stage is called the Rhuddanian stage, and its bottom boundary is consistent with the bottom boundary of the Silurian system that has passed on the Blue Star; the second stage is called the Aeronian stage (Aeronian stage). ), bounded by the bottom of the graptolite Demirastrites turriculatus belt; the uppermost part is called the Tritschian, bounded by the bottom of the graptolite Spiroraptus turriculatus belt.

② Wenlock system. The standard area is the Wenlock area in Shropshire, England. Divided into two stages, the lower Sheinwoodian and the upper Hormelian. The beginning of the Sheinwoodian, and also the beginning of the Wenlockian, is marked by the appearance of the Cyrtor-aptuscentrifuus belt; the Hommelian has the Cy-rtoraptuslundreni belt as the bottommost graptolite belt.

③ Rodro system. Standard area in the Rodlow area of ​​Shropshire, England

Silurian

Silurian

. It is divided into two stages, Gerstian and Lutherfordian. The base of the Gustian, that is, the boundary between the Wenlock and Rodlow lineages, coincides with the base of the graptolite Neodiversoraptusnilssoni belt, and the base of the Lutherfordian is equivalent to that of the graptolite Saetoraptusleintward-inensis belt. end.

④ Pridori system. The standard area is the Balland region in the Czech Republic and Slovakia. Its bottom boundary is the bottom of the Monoraptus parultimus belt, and its top boundary is the top boundary of the Silurian system. So far, this system has not been able to be further divided into several levels. Some people still have doubts about the level of this system, and even think that it is just a level rather than a system.

During the Silurian period, there were 9 main land masses in the world, including Gondwana, Laurentia, Europe (Baltic Sea), Siberia, Kolyma, Kazakhstan, China and North Korea, Tarim, and South China. The largest of these is the Gondwana Massif, concentrated in the high latitudes of the Southern Hemisphere. Other blocks were distributed in the middle and low latitudes at that time, especially the low latitudes. The ocean between the Laurentian and European plates is the Paleo-Atlantic. This paleo-ocean was once closed at the end of the Caledonian period, forming the Caledonian fold belt. The Appalachian Fold Belt formed after the closure of the pre-Appalachian Ocean between the Laurent Plate and the The Laurentian plate and the European plate collided at the end of the Silurian period, forming the European and American continent with extensive deposits of old red sandstone. The Siberian plate at that time was almost 180 degrees away from the current geographical position. The Kazakhstan plate was formed by the union of several intermediate blocks, between the Siberian plate and the Tarim plate. Regardless of the characteristics of fauna or sedimentary characteristics such as marine red beds, it shows that Tarim is between the Sino-Korean and South China plates. Between the two plates of China, North Korea and South China is the Qinling Ocean

Sediments from deep-water ocean basins of the Silurian period are rarely preserved. This is because multiple collisions and subductions between plates in the geological history almost wiped it out, and all that survived were the sediments from the continental shelf to the continental slope at that time. During the Silurian period, the continental surface seas and shelf shallow seas were widely distributed in the major plates, and platform carbonates were the most widely developed, and North America was the most typical. Its central part is widely distributed platform-type shallow-water carbonate facies, including the dolomite suites in the central and western parts of Yingjiang and western Canada, and the limestone suites in eastern Canada and the periphery of the dolomite suites. There is obvious lithofacies differentiation at the margin, that is, the dolomite sleeve turns westward into a transitional facies belt of limestone and mudstone, and then turns into a clastic facies belt westward. The eastern margin of North America also has a similar lithofacies differentiation, that is, from platform carbonate rocks to clastic facies belts to the east. Graptolite shale deposits in platform-type intervening basins are mainly found in continental Europe, especially in the Baltic Sea coast, Central Europe, and Eastern Europe. Obvious lithofacies and biofacies zoning from platform carbonate rock to platform margin slope graptolite shale appeared in Western Europe . The Silurian strata that deposited carbonate rocks and graptolitic mudstones on the Siberian platform were of very small thickness, while the active zones around them were formed by extremely thick carbonate rocks and volcanic flysch. The South China plate and even the middle block of Tibet and their peripheral active zones are all thought to be deposited mainly with carbonate rocks interbedded. The differentiation of lithofacies and biofacies of the Silurian in the South China plate is also very typical, that is, platform-type deposits of carbonate rocks and clastic rocks in the west, containing crustal fauna and graptolite fauna; clastic rocks and flysch in the east Basin deposits containing graptolite fauna. The Silurian Gondwana continent included vast areas of Africa, Oceania and South America. Similar deposits were deposited from northern Africa to the east and north of South America

Platform-type mudstones and fine clastics, containing the same Malvinokaffric fauna. Eastern Australia, Tasmania, and New Zealand are formed by large sets of flysch, which are deep-water deposits on the continental slope.

As far as invertebrates are concerned, the Silurian is unique in many ways. The most common fossils include graptolite, brachiopod, coral, etc. Graptolites are mainly monograptites, such as Monoraptus, Cyrtoraptus, Pristioraptus, and Rastrites, which were the main species in the Silurian marine floating ecological domain. The most striking class of creatures. In the early stage, there were representatives of di-graptolites extending from the Ordovician, such as Di-ploraptus and Climacoraptus. Graptolites are widely distributed and rapidly evolving, and the same species can be found on many continents in the world. According to the stage of graptolite evolution

Silurian echinoderms

Silurian echinoderms

The characteristics and special types of geological history have unique value in stratigraphic correlation. The determination of the boundaries of the Silurian clastic stages mainly depends on the graptolite belt.

The number of brachiopods is quite large, and they often occupy an absolute advantage in flat-bottomed organisms in shallow seas. Therefore, the Silurian era is known as the prime of life for brachiopods. The Wufangbei family, which usually has larger individuals, short hinge lines, and developed spoon-shaped platforms and wrist organs, is the most characteristic representative. They first appeared in the Late Ordovician and reached their peak in the Silurian. The Shiyan family with wrist snails and long hinge lines was first seen in the earliest Silurian period, and its origin is still a mystery. Since the Ordovician continuation, the non-cavity shellfish and windowless shellfish with wrist snails and short hinge line have been developing steadily. During the Ordovician, the Ordovician and Twisted Moon tribes declined significantly in the Silurian.

Corals and layer foraminifera are also two more prosperous categories in the Silurian Period, and they are commonly found in reefs, biomounds and biospheres. Silurian corals include radiant corals, bed corals and sun-radiated corals. There are many types and types of corals, and they reached their peak in the Devonian. The peak period of layer foraminifera is also in the Devonian period, so the Silurian period is their preparation period. These organisms are all extinct in today's oceans. They live a benthic lifestyle, so they have obvious regional distribution, but their larval stages can planktonic, which makes it possible for them to be widely distributed in suitable environments. middle.

Gastropods and bivalves continued to develop slowly into the Silurian. They are inferior to brachiopods in both abundance and diversification throughout the Paleozoic. Gastropods and bivalves are dominant in today's oceans, so studying their ecology and their living environment is of great significance for understanding these two categories in ancient times.

Compared with the Ordovician, the number of nautiluses in the Silurian cephalopods was significantly reduced. For example, the common endophytes in the Ordovician were extinct by the Silurian, and no new large groups appeared in the Silurian. The Xiushan Formation at the top of the Lower Silurian in the south of Huayan Kingdom is rich in nautilus fossils represented by Sichunocers, but they are not as good as the Ordovician in terms of quantity and differentiation.

Crinoids are the most successfully developed echinoderms in the Silurian period, and the petal crinoids (Petlocrin-us) and spiral crinoids (Spirocrinus) that are common in the Landovili strata of Huayan Kingdom are common representatives. Their individual shapes, compared with those in the modern ocean, vary greatly. Silurian Sea Ringo's Lifestyle Compared with Modern Times

Among arthropods, trilobites, which once dominated the Cambrian period, declined significantly in the Silurian period after a period of prosperity in the Ordovician period. In local areas and intervals, endemic molecules are still common and have important stratigraphic correlation significance. Examples include Coronocephalus and Se-nticucullus, which are common in southern China in Huayan Kingdom. Compared with trilobites, ostracods are far inferior, but can be quite abundant locally. Ostracods are also useful standard fossils from the Late Landovilis to the Pridoris. Eu-rypterids are the most important carnivorous representatives among Silurian invertebrates. They can swim. First appearing in the Ordovician, their strongest ecological impact was in the Silurian and Devonian. Unlike the ammonites in the cephalopods, Limulidae are not only found in the ocean, but also live in brackish water or even fresh water.

Conodonts still developed steadily during the Silurian period. It evolved rapidly and distributed widely. It has become another important fossil for comparing the Silurian strata after the graptolite. Also abundant in some types of deposits are Chitinozo, which are small, black individuals shaped like bottlenecks, sticks, or pellets. Its stratigraphic significance is also growing.

Celebrate the 7-day long holiday of National Day and enjoy reading books! Recharge 100 and get 500 VIP coupons!

Immediate recharge (activity time: October 1st to October 7th)