The Silurian Period is the last period of the Early Paleozoic Era and the third period of the Paleozoic Era, approximately 440 million to 410 million years ago. Generally speaking, transgressions occurred everywhere in the early Silurian. The mid-Silurian transgression reached its peak. In the late Silurian Period, various degrees of sea regression and land uplift occurred in various places, showing a huge transgressive cycle. In the late Silurian period, the crustal movement was violent, the ancient Atlantic Ocean closed, and some plates collided with each other, causing folds to rise in some places. The paleogeographic appearance changed dramatically, and the continental area expanded significantly.
At this time, marine organisms were still the dominant species. Among the organisms that inhabited the shallow sea bottom, brachiopods were the most numerous, with shell lengths that could exceed 80 centimeters. The development of spoon-shaped platforms and five-chambered clams began in the late Ordovician period. It reached its peak in the Silurian Period. The Holeless Shell Tribe, the Windowless Shell Tribe, and the Stone Swallow Tribe developed steadily since the Ordovician and later became the main groups of brachiopods. The Ordovician and Ordovician clams, which multiplied in large numbers during the Ordovician, declined significantly in the Silurian. Marine invertebrates played an important role in the Silurian period, and the species and internal components of each category changed. For example, graptolite animals retain the bigraptolite type, and the emerging monograptolite type is also relatively prosperous. The internal structural changes of brachiopods are relatively complex, such as the development of five-chambered mussels, sturgeons, and small-mouthed mussels. The mollusk cephalopods and nautiloids decreased significantly, while the bivalves and gastropods gradually developed. Trilobites began to decline, but Arachnids and Ostracods flourished. Among arthropods, the horseshoe crab is also called a sea scorpion.
It was widely distributed in the late Silurian ocean, and corals and stromatoporoids were also relatively prosperous, often forming reefs, biomounds, and biolayers. There are many types of radiant corals, beam corals, and sunburst corals. In addition to the prosperous marine algae, at the end of the Silurian Period, terrestrial plants began to develop from water to land, and naked ferns appeared for the first time. Due to the violent orogeny, the ocean area decreased and the land area continued to expand. As the pioneers of higher terrestrial plants, lower vascular plants began to appear and gradually occupied the land. Among them, naked ferns and lycophytes.
In the shallow sea, the jawless vertebrate fish that appeared in the Ordovician further developed, and evolved jawed fish began to appear, laying the foundation for later fish and higher vertebrates. The trilobites that were prosperous for a while began to gradually decline, and the plate-footed horseshoe crabs began to rise. They were the largest species of marine arthropods at that time. In the late Silurian period, early insects and arachnid arthropods appeared on land.
As the era goes by, the Devonian period is the fourth period in the Paleozoic era of geology and belongs to the Phanerozoic-Paleozoic era. About 405 million years ago to 350 million years ago, early naked ferns began to flourish. After the middle period, brachiopods and corals developed, and primitive ammonites and insects began to appear. In the late period, primitive amphibians and labyrinths began to appear, ferns and primitive gymnosperms appeared, and jawless animals tended to become extinct. Beginning with the Devonian Period, the earth began its Hercynian movement again, and many places began to rise, exposing the sea and becoming land. In the early Devonian period, naked ferns flourished. After the middle period, ferns and primitive gymnosperms appeared. In addition to corals, brachiopods, and stromatoporoids, invertebrates continued to flourish. Primitive ammonites, insects, and vertebrates also appeared. The fish in it developed unprecedentedly, so the Devonian is also known as the Age of Fish. In the later period, armored fish tended to become extinct, primitive amphibians began to appear, and brachiopods developed rapidly in the Devonian. The Lithodontidae that began to appear in the Silurian Period became important fossils in the Devonian Period. In addition, the division of perforated shellfish, lunar shellfish, unburrowed shellfish, and smallmouth shellfish is extremely important in and contrasting Devonian strata. Bubble and double-banded radiant corals were quite abundant at that time. In the early Devonian period, foam-type corals were dominant, and double-banded corals began to emerge. In the middle and late Devonian, double-banded corals dominated, nautiloids were greatly reduced, ammonites and tritons among ammonites flourished, and most of the orthograptolites became extinct. A small number of monolithic and bamboo-jointed stones remained in the early Devonian period, which began in the Ordovician. They reached their peak in the Devonian and became extinct at the end of the Devonian. Among them, thin-shelled and tower-joined stones flourished, and light-shell jointed stones flourished. Stones are also very important. The evolution of conodonts reached a peak of development in the Devonian. As early as the Devonian, the majority were jawless. Placoderms were quite prosperous during the middle and late Devonian periods. They had primitive jaws, even-finned fins, and were in a crooked shape. In the early Devonian period, naked fern plants were more prosperous, and there were a small number of lycophytes, most of which were simple in shape and small in size. In the middle Devonian period, naked ferns were dominant, but the primitive lycophytes were more developed, and primitive cuneiform plants and the most primitive true ferns appeared. In the late Devonian period, the naked ferns were on the verge of extinction, while lycopods continued to flourish. Nodular ferns and primitive cuneiform plants developed, and new true ferns and seed ferns began to appear. The climate at that time was still very warm, and terrestrial plants ranged from a small leafless plant to a tree-like plant up to twelve meters high, including ferns.
The invertebrates in the ocean are extremely rich, consisting of reef-building corals, sponges, echinoderms, molluscs and numerous brachiopods. The number of trilobites has been greatly reduced. In the Devonian period, they were the most important part of the earth's biological world. A time of great biological change. The large-scale march from the ocean to the land was the most prominent during this period, and the most important event was biological evolution. First, vertebrates entered a period of rapid development. All kinds of fish flourished unprecedentedly. The number and types of jawed fish and armored fish increased. Modern fish bony fish began to develop, ushering in the age of fish. In the late Devonian period, amphibian vertebrates that evolved from fish began the evolutionary process of leaving water and conquering land. Secondly, the terrestrial plants naked ferns have completely established themselves on land, and their three descendants, lycophytes, cuneiforms and true ferns, began to develop. By the late Devonian period, this type of plant composition appeared With vast tracts of forests, the earth is truly covered in green, turning the desert continent into an oasis.
One day 377 million years ago, the earth began to shake violently, the mountains shook, dust flew up, and dark clouds came to cover the sky. The sky darkened instantly, like night, and a large amount of high-temperature gas came from a certain seabed. The cracks spurted out, causing the nearby seawater to begin to boil, and smoke filled the sky. Many fish carcasses were floating on the boiling sea, and a strong fishy smell assaulted the nostrils. The river bed continued to tremble and suddenly exploded. More than 30 billion cubic kilometers of magma spewed out, bursting open the sea level and shooting straight into the sky. It broke up the thick clouds and burned the entire sky. In front of you was a dark red. . The falling rocks quickly destroyed all nearby coral reefs and other life. The magma not only greatly increased the temperature of the seawater, scalding thousands of creatures to death, but also polluted the seawater. The toxic substances in the magma react chemically with the seawater, causing the seawater to become acidic, and a large number of animals die because they cannot breathe. More than five thousand years after the disaster, pollutants in seawater spread into the atmosphere, most of which were greenhouse gases—carbon dioxide, causing global temperatures to rise rapidly, reaching 30 degrees Celsius, and ocean currents to stop moving. In the equatorial region, the seawater temperature rises from 20 degrees Celsius to 32 degrees Celsius, and more corals cannot survive the high temperatures and die. One hundred thousand years after the disaster, magma continued to erupt. At this time, there was no soil on the land. Due to the decay of plants, soil covered the ground and became a good nutrient for seaweed. The prosperity of seaweed consumed it. A large amount of oxygen accelerates the extinction of animals. Seventy-five years after the disaster, water vapor in the sky reacted with sulfur dioxide, causing acid rain. The flooding of acid rain for tens of thousands of years further reduced the number of plants and acidified the soil. The super plume broke through the ocean floor 1.3 million years ago, or 37,600 years ago. In the west of China, the earth began to tremble violently. From a volcanic crater with a diameter of 8,000 meters, 200,000 cubic kilometers of magma erupted. The magma flooded all places within a radius of 50 kilometers, and most land animals were on the verge of extinction. . The volcanic ash and toxic gases ejected from the volcano covered the sky and completely blocked the sun. The earth fell into a long night for more than two million years. For more than a million years, the temperature of the earth has continued to rise. Volcanic ash refracted sunlight, and the earth was unable to obtain solar energy. The sea water dropped from 32 degrees Celsius to 16 degrees Celsius. All the fish eggs in the shallow sea died immediately, and the earth fell into Severe ice age. One and a half million years after the disaster, the earth began to experience a heavy snowfall for more than a million years. This was the first and longest heavy snow in history. After the heavy snow lasted for several years, the creatures in the cold seawater began to Lots of death.
