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Triassic (the rise of reptiles and gymnosperms) is the first period of Mesozoic. It lies between Permian and Jurassic.

From 250 million years ago to 203 million years ago, it lasted about 50 million years. After the Hercynian movement, many geosynclines were transformed into mountain systems, and the land area expanded, resulting in some inland basins in the platform area. This new paleogeographic condition has led to changes in sedimentary facies and biological world. Since Triassic, continental deposits have been widely distributed all over the world, especially in China and other parts of Asia. In paleoclimate, the early Triassic inherited the characteristics of drought at the end of Permian; After the middle and late period, the climate changed to moist heat, which led to coal-bearing deposits in red rock strata and the development of xerophytes to moist heat plants. At the same time, the geographical areas of plants are also differentiated.

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Jurassic Period

Jurassic (about 208 million years ago ~ 65,438+44 million years ago, the era of reptiles and gymnosperms) belongs to the middle Mesozoic. The second period of Mesozoic. The stratum formed in this period is called Jurassic, which is located above Permian and below Cretaceous. Pangea, a super land mass, really began to split at this time. Cracks in the continental crust form the Atlantic Ocean. Africa began to split from South America, while India was ready to move to Asia.

Some important events in the history of biological development have attracted people's attention. For example, dinosaurs became the rulers of land, pterosaurs and birds appeared, and mammals began to develop. Terrestrial gymnosperms have reached their peak. The bivalves, gastropods, arachnids, ostracods and insects of freshwater invertebrates have developed rapidly. Marine ammonites, bivalves and arrow stones are still important members, and the six-coral has not changed much from Triassic to Jurassic. Echinoderm sea urchin has occupied an important position since Jurassic.

Reptiles developed rapidly in Jurassic. The lazy tooth is extinct, and so is the ocean magic dragon. The evolutionary type of dinosaurs-two of the four main bird hips flourished in Jurassic, and flying reptiles glided in the sky for the first time. The first appearance of birds is one of the important changes in the history of animal development. Another kind of dinosaur, sauropod dinosaur, flourished in the Jurassic period: one was a carnivorous dinosaur, and the other was a huge herbivorous dinosaur. Marine reptiles, mainly ichthyosaurs and plesiosaurs, have become members of the marine environment that cannot be ignored.

Some of the most primitive mammals that appeared in the late Triassic were on the verge of extinction in the late Jurassic. In the early Jurassic, other early types of mammals, Polyodon, were newly produced, which were considered to be herbivorous and extinct in the early Cenozoic. Ancient mammals that appeared in the Middle Jurassic are generally considered as the ancestors of marsupials and placental mammals.

Cartilaginous scleroderma began to decline in Jurassic and was replaced by whole bone fish. The earliest true bone fish discovered in Triassic developed greatly in the late Jurassic, with an increase in number, but fewer species.

In Jurassic, there were many evolutions of ammonites, which were mainly manifested in the complex suture lines, diversified shell ornamentation and shell shapes, which may be caused by ammonites adapting to different marine environments and various lifestyles. The Jurassic marine bivalves were abundant, and the non-marine bivalves also developed rapidly, which played an important role in the division and correlation of continental strata.

Jurassic is the heyday of gymnosperms. The development of cycads and ginkgo reached a peak, and conifers also occupied a very important position.

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the Cretaceous period

Cretaceous is the last period of Mesozoic. Cretaceous is the last period of Mesozoic, which began 65.438+0.37 billion years ago and ended 65 million years ago, during which it experienced 70 million years. Both inorganic and organic fields experienced important changes in Cretaceous. Located above Jurassic and below Cenozoic. Cretaceous is the period when the surface of the Mesozoic earth was flooded to the greatest extent. During this period, chalk was widely deposited in the northern hemisphere, which was named Cretaceous by Belgian scholar J.B.J Omalidaroi in 1822. The chalk layer is a very fine and pure powdery limestone, and it is a biogenic marine sediment, which is mainly composed of a calcareous nannofossil called chondrite and planktonic foraminifera fossils.

During this period, the mainland was separated by the ocean, and the earth became warm and dry. Flowering plants appeared, and at the same time, many new dinosaur species began to appear, including large carnivorous dinosaurs like Niu Long, Ankylosaurus members like Euphorbia, and herbivorous hadrosaurs like Lashiosaurus. Dinosaurs still rule the landing land, pterosaurs like airplanes, such as those gliding in the sky, and giant marine reptiles, such as sea dragons, rule the shallow sea. But the earliest snakes, moths, bees and many new small mammals also appeared in this period.

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All kinds of natural phenomena on the earth are constantly changing, and climate change is no exception. The difference is that climate change has gone through a long-span geological and historical period. Scientists reproduce historical climate change by studying historical meteorological records, ancient literature records, archaeological objects, geological and geomorphological phenomena and theoretical speculation.

Climate change in geological period

Geological evidence shows that in the whole natural history of the earth, at least nine tenths of the time is dominated by warm climate, such as early Paleozoic, from Cambrian, through Ordovician, Silurian to Devonian, which is 250 million years long; Throughout the Neogene, about 200 million years from Mesozoic to Cenozoic, the climate was mainly warm, including several short cold periods (ice ages). It is difficult to confirm the duration and influence scope of the ice age interruption period. Only from the study of stratigraphic sediments, it seems that there were great ice ages in Precambrian (600 million years ago), Carboniferous and Permian (350-225 million years ago).

In the last one million years, the cold climate dominated, that is, the Quaternary Great Ice Age. The arctic ice sheet has greatly extended to the mid-latitude area, reaching 57 degrees north latitude at the strongest time, and the thickness of the ice sheet in some places has reached 2 kilometers. There was a warm interglacial period in the middle of the Great Ice Age, and the change of cold and warm climate led to the rise and fall of glaciers. The study of glacial landforms in the European Alps shows that the Quaternary glacial period is divided into four glacial periods, separated by three relatively warm interglacial periods. Compared with the interglacial period, the snow line in the mid-latitude area can rise and fall by more than 1200m.

Among the fossils unearthed from Quaternary sediments in northern China, creatures representing cold climate and warm climate, such as the former, such as hairy rhinoceros, mammoth, saxifragon and fern, and the latter, such as rhinoceros, buffalo, elm and willow, proved the climate change in China in Quaternary. Another example is loess deposition and its underlying red soil layer, which is widely distributed in northwest and north China, showing a change from warm climate to cold and dry climate. In Quaternary, glaciers were distributed not only in the western mountainous areas of China, but also in Taibai Mountain in Qinling Mountains in the middle and east and Yushan Mountain in Taiwan Province Province.

About 1 10,000 years ago, the climate warmed, glaciers retreated, and the earth once again entered a warm interglacial period.

Climate change in human history

After the Great Ice Age, the climate in most parts of the earth was the warmest before 5000~ 3000 BC, which was considered as the best period after the Ice Age. At that time, the sea level was 2~3 meters higher than it is now, and the ice in the Arctic Ocean may have completely melted in summer. Now the Sahara desert in Africa and the desert in the Middle East, the climate at that time was much wetter.

From 900 to 450 BC, before the so-called early Iron Age, the climate in Europe entered a cold and humid period, and the glaciers in the Alps expanded significantly. Many peat beds from Ireland to Germany show that swamps were distributed on this vast land 2500 years ago; Most of the modern glacial remains found south of 50 degrees north latitude in the North American Rocky Mountains were formed during this period.

From 1000 to 1200, the climate in the northern and southern hemispheres has been in a suitable warm state, also known as the "second climate optimum period". At that time, the temperature in southern Greenland should be about 4 degrees higher than it is now. Due to the suitable climate, the vikings immigrated to Greenland in 982 AD.

From 1430 to 1850, the climate in the northern hemisphere turned cold, especially from 1650 to 1750, which was called the "Little Ice Age". With the cold climate, it is the increase of humidity and rainfall in the mid-latitude zone that makes the water level in the Caspian Sea more than 5 meters higher than that in previous and later centuries.

After 1850, the climate showed a warming trend again. With the improvement of modern scientific observation level, the study of climate change has a reliable data base, and the scientific principles of climate change are gradually revealed.

In every specific period, Baidu knows that there are ~ ~

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