The history of life on Earth during the Cambrian period was mainly a world of water, and all the ancient land that had been formed were child mountains and deserts, and were isolated and separated from each other, and did not have the conditions for biological reproduction. However, the oceans were very different, and before the Cambrian period there was a large number of algae breeding in the oceans, while many lower animals lived

The history of life on Earth

During the Cambrian period, it was mainly a water world, and the ancient land formed was full of mountains and deserts, which were isolated and separated from each other and did not have conditions for reproduction. But the ocean is very different, before the Cambrian period in the ocean there is a large number of algae reproduction, while many low-level animal activity in the algae among, into the Cambrian period, the Earth appeared extensive sea invasion phenomenon, the area of the ocean further expanded, for the growth of marine life to create the conditions, some primitive invertebrates gradually evolved into the development of invertebrates with hard shell. The most remarkable feature of the Cambrian is the mushrooming of different phyla of invertebrates with hard shells, these animals, including arthropods, mollusks, brachiopods, palaeocupids, as well as penaeid and dental spines. Their rapid emergence created a spectacular situation of biological explosion, bringing about a major leap in the evolutionary journey from shellless to shelled organisms. During the Cambrian period, the shallow sea expanded and the seawater was warm, containing normal salts and large amounts of dissolved calcium carbonate, which met the needs of invertebrates to secrete hard body bones and enhanced self-protection. The Cambrian period is often referred to as the "trilobite era". The trilobites first appeared with the small shell fauna at the beginning of the Cambrian, which mainly refers to soft-tongue snails, gastropods, veneers, rostral shells and a large number of tiny (usually only 1-2 mm), low-level mollusks of unknown taxonomic position. Trilobites have complex developmental stages. Trilobites are dioecious, oviparous, and go through three growth stages during their lifetime development, namely juvenile, segmented, and adult stages. It takes several molts to grow into an adult, and many of the present-day arthropods inherit the trilobite growth pattern. Some species of trilobites like to swim, some like to float on the surface, some like to crawl on the sea floor, and some are used to living in the mud and sand, they occupy different ecological spaces, and the Cambrian ocean became the world of trilobites. The number of trilobites decreased in the Late Paleozoic with the emergence of numerous marine invertebrates, and finally became extinct when the Mesozoic came. The perfectly preserved fossil group of Chengjiang animals with only soft bodies found in Yunnan by Chinese paleontologists became famous overseas, representing a high level of biodiversity in the Cambrian. Later in the Cambrian, cephalopods and penstocks appeared.

The Ordovician was the most extensive period of sea invasion in the Early Paleozoic, which created favorable conditions for the further development of invertebrates. During this period, marine invertebrates were not only abundant in terms of phyla and genera, but also had important divergences in ecological habits. In addition to trilobites, there were also penstones, nautilus, tooth-shaped spiny animals, brachiopods, gastropods, etc. Primitive fish also appeared in the Ordovician. At that time, there were various kinds of penstones floating around in the ocean, various nautiluses feeding around, trilobites and brachiopods crawling slowly in the "jungle" of sea lilies, and many worms and arthropods hiding in the algae and mud, a vibrant scene. It is impossible to talk about the Ordovician without mentioning the nautilus, which flourished in the Ordovician oceans. The nautilus belongs to the group of cephalopods, which all live in the oceans, from shallow to deep oceans, from tropical to cold zones. If we refer to invertebrates as lower animals and vertebrates (including humans) as higher animals, then cephalopods are the most advanced species of the lower animals. They include squid, octopus and nautilus. Their bodies are symmetrical on both sides, and their heads are extremely well developed with a pair of sharp eyes. They are called cephalopods because their heads and feet are all developed on the same side of the body, and the feet split into 8-10 wrists or tentacles around the mouth of the head, enabling them to catch prey and defend themselves from enemies. Cephalopods belong to the phylum Mollusca, so they also have shells, but some species have shells outside the body, while others have shells inside the body or have degenerated and disappeared. Cephalopods have a brain composed of the ganglia of the head and are dioecious. Therefore, from any point of view, cephalopods are distinctive and very progressive creatures among invertebrates, and they appeared from the Cambrian period and quickly developed into a dominant marine species in the Ordovician. The most widely distributed cephalopods in the Ordovician ocean were hornblende. Hornblende have a hard shell, which, as the name suggests, is shaped like the horn of a cow or sheep, and is usually straight, but can also be curved or coiled. Another group of cephalopods, the chrysopods, would appear in large numbers and play an important role in the Mesozoic.

During the Silurian, the Earth's surface changed considerably. The oceans shrank in size, and land was created and gradually expanded. With land came plants, and the lower plants entered the history as the pioneers of the plant world. In the oceans, invertebrates continued to flourish, ignoring the shrinking of their territories, because the oceans were too large, not to mention that a new sea invasion would follow. At the end of the Silurian, the "Caledonian movement", or the folding and mountain-building movement at the turn of the Silurian and Devonian, took place. The typical area is Scotland (the old name for Scotland) in the north of England, extending to Norway in the west of Scandinavia. There are folded mountain systems and highly metamorphosed rocks that have had a significant impact on global geological and biological evolution. At the end of the Early Paleozoic, the ancient Atlantic Ocean closed, thus allowing the North American plate to collide with the Russian plate and form the "Lawa continent". The Qilian Sea folds were closed when the Qaidam Plate in western China merged with the Chinese and Korean plates. Many other ancient oceans (e.g., the ancient Toral Ocean, the ancient North Asian Ocean, the ancient Pacific Ocean, the proto-Tethys Ocean, etc.) were affected by the Garridon movement to varying degrees, resulting in the accretion of the crust at the margins of the continental plates. The land area further expanded and the ancient terranes became more stable. In the Silurian ocean, more species of corals appeared, and they laid the foundation for the unprecedented prosperity of corals in the Late Paleozoic (mainly Devonian and Carboniferous). Penstones belong to hemiceratops, also known as stomatopods or cryptoceratops, which generally have worm-like bodies, symmetrical from left to right, all living in the ocean. Hemisauropoda was once classified as a subphylum of the Chordata, on the grounds that its oral cords were equivalent to the chordata's spinal cords, and was probably the most primitive class of chordata. However, some scientists believe that the oral cord may be an endocrine organ, rather than a structure equivalent to the notochord. From the available research data, hemichordates are a transitional type between non-chordates and chordates, and the emergence and flourishing of Silurian penstones herald the emergence of a forerunner of higher organisms. Penstones are all extinct, and we can only recognize them today by their fossils, which are usually preserved at the rock level and resemble the traces of writing with a pen, hence the name penstones.

The Devonian was the first epoch of the Late Paleozoic, starting at 405 million years ago and lasting for 55 million years, and the strata formed during this period are called the Devonian by geologists. The Devonian was first studied in Devonshire in southwestern England, and Japanese scholars later translated Devon into the katakana "Devon". It was only from this period that organisms began to develop from the sea to the land, after the Devonian period, when the biological world underwent a dramatic change from the sea to the continents.

At that time, fish were the first to diverge from invertebrates, forming a new family of biology. The Devonian period is also known as the "Age of Fishes" because of the unprecedented abundance of fish in the Devonian. The early fishes were primitive, without the differentiation of upper and lower jaws, and only later did more advanced types appear.

In the dry and hot environment of the time, the gradual drying of the water prompted a part of the fish to crawl in the mud with their fins, and when the fleshy fins evolved into limbs that allowed them to crawl into the woods, a new phylum emerged, which was the amphibians. In fact, the landing of some plants out of the ocean objectively set the stage for the development of the biotope and was therefore a major event in the history of biological evolution. On the other hand, invertebrates in the oceans still ruled the world there. Brachiopods, corals, laminaria, moss worms, bivalves, tooth-shaped spines and other organisms competed in the oceans, among which brachiopods are a very remarkable class of organisms. Brachiopods are benthic, sedentary organisms with a soft body protected by a two-petal shell and, in addition, a fleshy stem for supporting and anchoring the body. They prefer to live fixedly on the quiet bottom of the sea, where they are uncontested. There are many varieties of brachiopods, and in the strata of this period in the south of China, there are abundant brachiopod fossils, and the Devonian system of Guangxi is called the "treasure basin" of brachiopod fossils, where you can see stone swallow shellfish, twisted moon shellfish, holeless shellfish, perforated shellfish, long-bodied shellfish and other kinds of brachiopod fossils everywhere. Corals also flourished during the Devonian period, and corals were sensitive to the effects of climate, and group reef-building corals were distributed in tropical and subtropical zones, while in temperate and cool climates were mainly small single corals. According to the ecological types of organisms, scientists have classified three types of organisms in the Devonian oceans: reef-phase organisms, mainly referring to corals and laminaria; shell-phase organisms, basically composed of brachiopods and bivalves; and planktonic-phase organisms, composed of organisms such as chrysolites, penstones and tooth-shaped spines. This provides us with further understanding of them, and the differentiation of organisms is an important basis for delineating biotope assemblages and ecoregions.

The Carboniferous is a representative period of the great flourishing of the plant world. The Carboniferous period began 350 million years ago and lasted for about 65 million years. The strata formed during this period were rich in coal, hence the name "Carboniferous". According to statistics, the coal reserves belonging to this period account for more than 50% of the total reserves in the world.

In the forests of the Carboniferous period, there are both tall trees and dense shrubs. Among the trees, wood sorrel has deep roots and leaves, and the stems of wood sorrel can grow to 20-40 cm thick. Stone pines are another group of trees, which are majestic and spread in patches, with the tallest ones reaching 40 meters. During the Carboniferous period, gymnosperms (e.g., Sugae, Pinus sylvestris, Ginkgo, etc.) began to appear, and they generally have large pinnate leaves and tall trunks. However, ferns are the most abundant. Ferns are the exuberant family in shrub forests, and although they are low, they occupy a large amount of the lower space of the forest. During the Carboniferous Period, the land of Shanxi experienced several invasions of seawater and frequent alternation between sea and land. Whenever the seawater receded, land plants flourished rapidly in the warm and humid environment, and one period after another the forest was generated. The Permian was an important reef-forming period in the history of the Earth's development. At that time, the seawater was warm and clear, and various kinds of calcareous algae and sponges that like to live in shallow waters proliferated. It is hard to imagine that soft sponges could build reefs, but in fact, these small and insignificant animals have their own calcareous skeletons, and they were wrapped by algae after death in large numbers, and finally formed thick reefs over time. Through comparative studies of Permian bioreefs around the world, scientists have found that they share many common features, thus laying the foundation for further revealing the secrets of oil and gas formation. How are bioreefs related to the formation of oil and gas? Bioreefs are formed by various reef-building organisms during geological history, and the types of reef-building organisms vary from time to time. These reef-building organisms include calcareous algae, archaea, calcareous sponges, corals, moss worms, laminaria, thick-shelled clams, etc. After years of continuous growth, the reef-building organisms can build strong wave-resistant structures in the ocean, and their scale and size are completely comparable to those of coral reefs in the modern ocean. Many Permian reef-type oil and gas fields have been discovered around the world, but the extinction of a large number of biological phyla at the end of the Permian period reduced the number of reef-building organisms in the ocean, and there were no reefs of that scale that could form and store oil and gas resources throughout the Mesozoic.

The Triassic was the first epoch of the Mesozoic, and the first strata representing this period were found in southwestern Germany. The color and rock structure of this set of strata clearly consisted of three parts: the lower part was terrestrial mixed-colored sand shale, the middle was marine gray-white limestone, and the upper part was terrestrial red rock, and the nature of the three parts was clear, so it was called "Triassic".

At this time in the ocean, with the end of the Permian extinction of a large number of biological phylum, replaced by mollusks (chrysolite, bivalves, etc.), six-shot coral, sponges, sea lilies, foraminifera, moss worms, etc., microfossil tooth-shaped spines in the Triassic is very common, they are in the evolutionary history of the key period, the genus species turnover appears to be extremely frequent, to the end of the Triassic they all extinct. On land, the gymnosperms continued to dominate, with the siderophores dominating, and the true ferns and wood sorcerers gradually flourishing. Terrestrial vertebrates such as water dragons and canine jaws emerged, which are mammal-like reptiles close to their mammalian ancestors. In order to adapt to survive in a semi-arid environment, amphibians emerged as tailless types, which are frogs and toads. The late Triassic reptiles diverged in all directions and were diverse. At the end of the Late Paleozoic, there was a crustal movement, which geologists call the "Hercynian movement", after which many active troughs in the Northern Hemisphere were successively transformed into folded mountain systems, and influenced the evolution of the crust in the early Triassic. Therefore, from a global perspective, the scale of Triassic sea erosion was not very large, and the sea erosion area was limited to a narrow zone between the north and south continents in the near east-west direction, i.e., the Mediterranean-Himalayan trough, and the trough areas on the east and west coasts of the Pacific Rim. In China, the Triassic has formed a boundary that is continuous from ancient Kunlun to ancient Qinling to ancient Dabie Mountain. The vast area north of this boundary is inland basin-type sedimentation, with red strata formed under dry climate and coal- and oil-bearing rock systems deposited under semi-dry thermal and warm-humid environment in the middle and late Triassic. To the south of this boundary, it belongs to the marine sedimentary area, mainly deposited to form limestone and other marine strata, therefore, we can call the paleogeographic landscape of China in the Triassic period "South China Sea North Land". However, this situation began to change in the middle and late Triassic, the seawater in South China from the eastern stable shallow sea area to the western trough retreat, the end of the Triassic, a crustal movement called "Indo-Chinese movement", the impact of Indo-Chinese movement, South China almost all exposed to the sea and North China, the seawater is limited to the southwest margin, the emergence of a continental environment dominated the paleogeographic landscape, from then on to end The situation of "South China Sea and North China Land" in the eastern part of China was ended, and the sedimentary differences between the north and south disappeared. At the same time, a new tectonic pattern began to form gradually from the Late Triassic, and the crustal movement turned to rise in the east and fall in the west, and the sedimentary characteristics of east-west divergence in China's continent gradually showed up, which is also the sedimentary characteristics of China's entire Mesozoic. This, in turn, inevitably affected the formation and distribution of mineral resources. In the Alps of France and Switzerland, there is a Jura Mountains, and some of the theories or concepts applied in geology today are based on the understanding of the Jura Mountains at that time, such as the "fossil sequence law" in paleontology, the establishment and division of fossil belts, and the concept of "order" in stratigraphy. Since the stratigraphy of this area is particularly well developed, it has been determined to have been formed in the middle of the Mesozoic period of geological history, and is therefore called Jurassic.

The Jurassic period was a time of great reptile prosperity. At that time, the Earth's climate was warm and humid, and in many parts of the globe there was surprisingly no difference between tropical and temperate zones. These conditions were very favorable for dinosaurs to flourish, and they quickly took over the land, sea, and sky. During the Mesozoic, mammals had not really emerged, so reptiles such as dinosaurs had no rivals for survival, and they rightly became the true overlords of the biological world.

According to the pelvic type of dinosaur skeleton, terrestrial dinosaurs can be divided into lizard-rumped and bird-rumped. Lizard-rumped dinosaurs are further divided into herbivorous lizard-footed dinosaurs and carnivorous theropods. The former dinosaurs were generally large, had small heads and long tails, and walked on all fours; the latter dinosaurs had specialized forelimbs, strong hindlimbs, sharp teeth, and were good at predation. In the late Jurassic period, the emergence of primitive birds was another important event in the history of biological evolution, which was a change in the evolution of reptiles to birds.

The rapid development of reptiles such as dinosaurs, especially the terrestrial dinosaurs, which were able to occupy the surface of the earth, depended mainly on the presence of land plants. The warm climate at that time was very beneficial to the survival and reproduction of terrestrial plants. Low ferns grew into dense shrub forests, and tall gymnosperms were sundews, ginkgoes and pines and cypresses, and trees and shrubs mixed with each other. This period was very beneficial for the formation of coal. Many of the world's largest coal fields were formed during this period. The environment began to change in the late Jurassic, with high volcanic activity and a dry and hot climate. The sedimentary conditions in the late Jurassic were complex, and terrestrial invertebrates were mainly bivalves, lobate limbs and mesozoans, but the number of fish in lakes gradually increased, and wolffin fish are common fish fossils in the Jurassic.

On the other hand, the oceans are still a mysterious world. During the Jurassic, the invertebrates in the ocean were mainly chrysolites and bivalves. Chrysolites belong to the cephalopod class of the mollusk family, the same family as the nautilus, and are an important fossil to delineate contrasting strata.

The Cretaceous is the last epoch of the Mesozoic, and the name "Creta" comes from Latin, representing a grayish-white, fine-grained calcium carbonate deposit, which forms the steep walls of the Dover Strait in southeastern England, where the Cretaceous strata were first recognized. The Cretaceous is the first epoch in geological history to be named after its lithology. The Cretaceous was an important period in the history of the Earth's development, a period when the new phylum of plants and animals flourished and evolved rapidly, and a period of global continental drift and another great biological extinction. Dinosaurs once occupied the world stage at that time, and the famous Tyrannosaurus Rex was the most powerful carnivore at that time. Most of the lizard-rumped dinosaurs, represented by Tyrannosaurus rex, were highly adapted to hunt their prey, and they were found all over the world. The evolution of ornithischians was also very striking during this period, with the emergence of Aetosaurus, Ceratosaurus, and ornithopods, and Duck-billed dinosaurs were very common ornithopods. In addition to the dinosaurs on land, the Cretaceous period saw the development of reptiles that were better adapted to the air, not only were they large, but their ability to fly was comparable to that of some birds; the reptiles in the sea were represented by Cricetosauria and Serpulosauria. However, the rise of birds, mammals and fish throughout the Cretaceous period has posed a threat to dinosaurs, and the pattern of dinosaurs dominating the world, which continued from the Jurassic period, is facing collapse. Among the fish, the true bony fishes developed rapidly and were distributed all over the world. After the Mesozoic era entered the Cretaceous period, the most important event was the successive extinction of various dinosaurs, making the Mesozoic era, the dominant biological world all withdrew from the stage of history, thus ending the era of dinosaurs that ruled the earth for more than 100 million years. Scientists further pointed out that the catastrophe did not just fall on the dinosaurs, at the end of the Cretaceous period, there was a catastrophe throughout the biological world.

Scientists have pointed out after research, the end of the Mesozoic era to dinosaurs as the representative of the biological extinction, following the end of the Paleozoic Permian biological extinction after another notable event. In addition to dinosaurs, this event also led to the complete extinction of chrysolites and aragonites; foraminifera, corals, sea lilies, bivalves and some orders and families of microscopic paleontology were also completely extinct. Statistics show that the catastrophe at the end of the Mesozoic era affected a total of 3,000 genera of various organisms, more than half of which were eliminated. Scientists believe that the sudden extinction of organisms in a short period of time can be seen as the regulation and balance of their own evolutionary process, which is an important factor in promoting the continued development of organisms. From the characteristics of the Cretaceous sedimentation in China, the biological survival conditions at that time were indeed very harsh, with the vast majority of the area belonging to the dry zone, while North China and Northwest China had semi-arid climatic conditions, and only the northern part of Northeast China had a temperate and humid climate. Due to the dry and hot climate, the strata formed by the deposition are mainly red rock system. There have been frequent volcanic eruptions along the near Pacific coast throughout Asia.

The Mesozoic era was dominated by dinosaurs, and at that time, a small reptile lived in the jungles and grasslands in a dodgey way, which is the theropod, with incisor, canine and cheek teeth, which are different from the general reptiles. The spinal structure of theropods is also very complex, and the limbs are erect to the bottom of the body, which indicates that they are an agile and good at running animals. Further development of the theropods led to the emergence of the triclinic theropods, whose body structure features are closer to those of true mammals and are widely distributed in Europe, Africa, North America, and China. Scientists call them mammal-like reptiles. The skeletal structure of mammals is stronger and more compact than that of reptiles, and it is easy to preserve a complete skeleton. However, fossil teeth are more important to mammals in the classification and identification of fossils. Mammals have mammary teeth in their infancy, and the permanent teeth that sprout during development and growth do not change with the growth of the body, while the teeth of various mammals have different characteristics, so we can classify and identify them as long as they are based on the types and characteristics of teeth.

When the crustal movement intensified at the end of the Mesozoic and the environment changed significantly, reptiles such as dinosaurs had difficulty in adapting and surviving, while mammals showed a strong competitive ability. Mammals have the ability to adapt well to their environment, have a constant body temperature, have mammary glands to nurse their young, have a well-developed brain to dominate their movements, are fecund (except for monotremes), facilitate the continuation of offspring, and so on. All these provide their own advantages for their growth and development. After the Cenozoic, the placental species (true animals) became the mainstream of the mammalian family, and the majority of fossil and extant mammals belong to the placental species. The majority of fossil and extant mammals belong to placentals. They evolved rapidly, and in addition to land, they completed the development of radiation to the sea (e.g., cetaceans) and to the air (e.g., bats) in a very short period of time. There are about 30 orders of placental mammals, including carnivora (e.g., felines), rodents (e.g., rats), even-toed (e.g., pigs, cattle, sheep), odd-toed (e.g., horses, donkeys), primates (e.g., monkeys and apes), pteropods (e.g., bats), proboscideans (e.g., elephants), and cetaceans (e.g., dolphins). Placeless species also gained space in places such as Australia, where marsupials became the masters. Birds have formed numerous orders and families in the Tertiary period, laying the foundation for today's classification. The genera and species of birds are numerous and now amount to more than 8,500 species. The Quaternary vertebrate mammals developed rapidly, and the total phylum was similar to the Tertiary, but the evolution of genera and species was remarkable and the number increased rapidly. Representative fossils include: Sanmen horse, saber-toothed tiger, swollen-boned deer, giant panda, ancient rhinoceros, Yang's tiger, Chinese hyena, etc. Special mention should be made of the appearance of paleofossils from the early Quaternary period (about the Middle Pleistocene).

The development of mammals culminated in the emergence of humans with the ability to transform and conquer nature. The essential difference between humans and all other higher animals is the ability to make tools and to use them for labor. Therefore, the evolution and development of humans has written a glorious page in the history of mammalian development and is a significant event in the history of biological evolution. The process of human development is divided into the early ape stage, the late ape stage, the early hominid stage and the late hominid stage. The earliest apes walked on all fours and lived in tropical forests. Due to environmental changes, the forest area shrank, and some apes migrated to live on the plains and began to stand upright and obtain food through labor, and later further walked with their hind limbs, and produced language and communication in labor, finally developing into human beings.

Previous：Where does the earth's matter come from?

Next：Origin of World Earth Day