Permian, the last days of the Paleozoic Era, the Earth became a purgatory

For the past

Humans always have a natural curiosity and awe

For life

There are still many unknowns waiting to be explored.

The baton of time was soon passed to the Permian period, the last era of the Paleozoic Era and the cruelest era in the history of the Earth so far. Starting from the Cambrian explosion of life, after more than 200 million years of biological evolution, organisms moved from the ocean to the land, from primitive to complex, and finally on the Permian continent, the biological appearance was relatively complete. Due to the collapse of forests on land, reptiles replaced amphibians and became the new generation of dominant organisms; in the ocean, cartilaginous fish dominated by sharks continued to dominate, ammonites and brachiopods flourished again, and trilobites were still lingering; the living environment of the Permian period seemed to be like the Earth today, plain and diverse, and the biological appearance gradually became normalized. However, when everything was on track, it fell into a trough again. At the end of the Permian period, the most serious biological extinction event in the history of the Earth occurred, 95% of the Earth's creatures were wiped out, and the Earth ushered in the most tragic night.

The Permian: The Rise of Reptiles

The end-Permian mass extinction event

The Permian (symbol P) is the last period of the Paleozoic Era, dating back 298.9 to 251.9 million years, and lasting for 47 million years. It began with the first appearance of the conodont Streptognathodus isolatus and ended with the first appearance of the conodont Hindeodus parvus. The stratigraphic stratification of the Permian is very obvious, which is also the origin of its name. "Permian" was first proposed by British geologist Roderick Murchison (1792-1871) in 1841, named after the strata near the town of Perm in the South Ural Mountains of Russia. Later, when Chinese scholars translated Permian, they translated it as Permian because the stratigraphic dichotomy of the German Permian was more obvious, with the upper part being magnesian limestone containing copper ore and the lower part being red sandstone without copper ore.

An imagined picture of what life looked like in the Permian

Due to its obvious dichotomy, the Permian was divided into the Lower Permian and the Upper Permian according to the "dichotomy" method before the 1990s. But in fact, due to the differences in the Permian systems around the world, the meanings of "Lower Permian" and "Upper Permian" in different regions are not necessarily the same. In order to facilitate the division and comparison of the Permian system around the world, scientists from China, the United States and Russia discussed together and finally formulated a "three-part division" plan for the Permian system, which divides the Permian system into three systems and nine stages. Among them, the Ural System (Cisuralian) is based on the strata in the southern Ural Mountains of Russia, the Guadalupian System (Guadalupian) is based on the strata in the Guadalupe Mountains of Texas, the United States, and the Lopingian System (Lopingian) is based on the strata in South China, China, including the famous Wujiaping Stage and Changxing Stage. The Permian marine strata, especially the Lepingian marine strata, are the most complete in South China, China, so China is also a world leader in the study of the Permian mass extinction event.

International Stratigraphic Timescale—Permian

Changxing Meishan Golden Nail

Age of Behemoths: Rise of the Reptiles

Climate change is often the main factor affecting biological evolution. For example, the last humid, oxygen-rich environment created the "giant insect kingdom" in the tropical rainforest of the Carboniferous period, while the cold and dry climate from the end of the Carboniferous period to the early Permian period led to the rise of another type of creature, the more advanced "reptiles". The Permian period is also called the "Age of Giants" because of them.

Dimetrodon was a powerful predator

Reptiles appeared in the Pennsylvanian Period of the Carboniferous, but they were still a minor role when they appeared. Amniotic eggs are a characteristic of reptiles, or in layman's terms, "eggs", which can be laid on land away from water. In the previous chapter, we talked about the rainforest collapse event at the end of the Carboniferous period, which caused the forest to disappear and turned into scattered oases in the desert. Amphibians and insects that rely on water sources have to stay in small oases, and species have suddenly decreased. At this time, reptiles with unique structures stood out and were able to travel long distances between different oases. Therefore, in the Permian period, reptiles quickly became the dominant species, and their body size changed from skinny lizards to large mammals.

Wolf lizards fighting for prey

Although all reptiles are called amniotes, they soon differentiated into two different types. They are the Synapsids (Synapsids) and the Diapsids (Saurischia). Synapsids have one inferior temporal fenestra on each side of the skull, while Saurischia have two temporal fenestra on each side of the skull, hence the names Synapsids and Diapsids. The typical representatives of Saurischia are quadrupedal reptiles such as dinosaurs, crocodiles, and turtles. Even birds evolved from dinosaurs are classified as Saurischia, which has continued to this day; Synapsids are called "mammalian-like" and are the ancestors of all mammals. The Pelycosauria to which Dimetrodon belongs is its representative, but Synapsids became extinct in the Cretaceous period, and the mammals evolved from their descendants eventually ruled the world. Students who have read Permian biology books may be confused by the various complex "beasts" and "dragons" of this period. It is true that reptiles have become more diverse since the Permian period, with great differentiation and many different species. But to put it simply, those called "beasts" generally belong to the therapsids of the synapsid class, and most of the "dragons" belong to the Saurischia class, with a small number of pelycosaurs of the synapsid class, such as (ignore the synapsid Dimetrodon, and don't ask me why Aarchotherium belongs to the Saurischia class!)

Reptile evolution tree

Mammals evolved from synapsids in reptiles

Dimetrodon is a representative of the Permian synapsids

Dimetrodon, a sphenodon, is one of the ancestors of mammals. It flourished in the early Permian period, ushering in the "Age of Giants". It was characterized by a sail up to 1 meter high on its back, which was probably used to absorb solar energy to maintain body temperature or to seek mates. It was the strongest carnivore at the time. Dimetrodon is similar in shape to Spinosaurus, but not as strong.

Dimetrodon had a huge dorsal sail

Dimetrodon fossil

Inostrancevia, a synapsid, was one step closer to mammals in terms of classification. It appeared in the Lepingian period and eventually became extinct due to the mass extinction at the end of the Permian period. Inostrancevia fed on sauropods such as Scutosaurus and Scutosaurus, which means that the ancestors of mammals ate the ancestors of dinosaurs (for sure).

Wolf lizard beast restoration

Lycosaur fossil

A wolf lizard with sharp teeth is hunting a scutosaur

Scutosaurus, a parareptile belonging to the order Ankylosauria, is distinguished from true reptiles by the lack of a hole under its skull. It is a vegetarian with a large body and is often ambushed by other carnivores in documentaries.

The Scutosaurus is being hunted by the Lycanthosaur again

Lystrosaurus, a synapsid theridicynodont, lived from the late Permian to the early Triassic. It was a burrowing creature that survived the Permian mass extinction and one of the few creatures that serve as evidence for the theory of continental drift. Lystrosaurus was pig-like, so it is a more distant relative of humans.

Burrowing Lystrosaurus Survived the Mass Extinction

Similarly, in order to adapt to the dry environment, plants evolved seeds that can be used for reproduction, and gymnosperms came onto the historical stage. After the collapse of the rainforest in the Carboniferous period, gymnosperms began to emerge. Independent seeds store the nutrients needed for germination, which is much stronger than ferns that rely on water to germinate spores. In the Permian period, gymnosperms such as seed ferns, cycads, ginkgo, pines and cypresses quickly became the dominant land plants, and even dominated the entire Mesozoic era.

Modern gymnosperms

The birth of Pangaea

Do you still remember the theory of continental drift proposed by Wegener (1880-1930)? Today, plate movement has become one of the most important theories in earth science. Continents in the world will eventually unite after a long period of separation, and when all the continents in the world unite together, they will form a supercontinent. The supercontinent closest to us is the "Pangia" supercontinent formed during the Permian to Triassic period, also known as Pangaea and Pangaea. Pangaea actually began to converge in the Devonian period 390 million years ago. After 100 million years of drifting, Laurentia in the north and Gondwana in the south kept approaching and rubbing against each other, and finally completely collaged together at the equator around 250 million years ago. Supercontinents are indeed as described in middle school textbooks. Judging from paleontological fossils, landmark strata, rock walls, paleomagnetics, special magmatic activities and other means, there was only one Pangaea and one Pan-Ocean in the world in the late Permian period. This unique environment also had a huge impact on the environment. Ocean currents were blocked and there was a lack of fresh water in the inland, which is also an important reason for the widespread Permian desert.

The supercontinent Pangea was formed in the Lepingian (Late Permian)

Pangea is not the oldest supercontinent, but it is the first supercontinent that humans have identified. Rodinia and Columbia, which were related to the Snowball Earth in the Precambrian period, were mentioned in the Precambrian chapter of the first issue. Today, the Earth is in the formation stage of the next supercontinent. It is estimated that in 200 million years, the Pacific Ocean will close and Asia will unite with the Americas to form a new "Amasia supercontinent."

The modern continents were formed after the breakup of the supercontinent Pangea

Now on the way to the formation of the American-Asian supercontinent

Sharks rule the ocean

The Permian period was accompanied by the formation of supercontinents, and the ocean also formed a unique super ocean - Panthalassa. After the Devonian mass extinction, the dominant cartilaginous fish still dominated the underwater world. They were early sharks, and the sharks at this time may have been slightly different in appearance...

Helicoprion is a representative of alternative sharks. Since sharks are made of cartilage except for their teeth, only their teeth can be preserved as fossils. The fossils of Helicoprion are a plate of shark teeth arranged in a spiral, which undoubtedly poses a huge challenge to paleontologists. In order to restore the prototype of Helicoprion, attempts have been made to put spiral teeth on the head, fins, and tail. Finally, the latest fossil CT technology was used to scan the preserved spiral tooth fossils, and it was clearly pointed out that this spiral tooth grew deep in the jaw and was used to "suck" ammonites. Helicoprion also surprisingly survived the mass extinction event at the end of the Permian period.

Helicoprion sharks are avid fans of soft-shelled seafood

Restoration of Helicoprion in different eras

Correct simulation of Helicoprion teeth

In addition, other sharks also have strange shapes. The Xenacanthus has spines on its head, which are used for defense or reproduction, which is also a common feature of freshwater sharks; the dorsal fin of the Carboniferous pectoral shark (Stethacanthus) is like a planer, which is very different from the dorsal fins of modern sharks, indicating that the structure of sharks has been improving.

A spiny shark roams the water

The dorsal fin of the pectoral shark is like a planer

Sharks have been the top predators in the oceans thanks to their agile bodies and constantly evolving body forms, and this is still the case today. 60% of sharks are able to give birth to live young, and this advanced reproduction method has greatly improved their ability to survive. Their strong ability to quickly adapt to the environment has allowed them to survive the most severe mass extinction.

Modern Sharks Ride the Ocean

The sky is falling and the earth is cracking, a long-planned crisis

The most well-known thing about the Permian period is its tragic ending. The mass extinction at the end of the Permian period is the most devastating biological extinction event on Earth so far. 95% of species disappeared, including 75% of land animals and 96% of marine life. For 10 million years, the entire Pangaea continent was littered with corpses, and the seabed was covered with the bones of weak creatures. Most of the creatures that were born in the Cambrian biological explosion completely withdrew from the stage of history. Trilobites, horseshoe crabs, tetracorals, horizontal plate corals, and worms that had survived for many eras completely disappeared. Up to 90% of other animals such as brachiopods, bivalves, cephalopods, and conodonts were wiped out. Almost all non-cavernous creatures on land also suffered a catastrophe. This tragic mass extinction event was not caused by an extraterrestrial body, but a disaster that the Earth had planned for a long time.

Image of the Permian mass extinction

The most direct cause of the end-Permian mass extinction was a sudden global environmental change, and the cause of the sudden environmental change was most likely large-scale volcanic activity. There is a kind of magma activity that is known as the most violent on Earth. The magma comes from deep in the mantle and originates from the boundary between the core and the mantle. The coverage area can reach millions of square kilometers in diameter, and the entire Earth will be plunged into a haze. That is the "super mantle plume". Ordinary mantle plumes also come from the core-mantle boundary or the mantle transition zone, which can produce large igneous provinces (magma constructions composed of large-scale mafic rocks and radial dykes formed on the surface), while super mantle plumes are much larger in scale and can even continue to erupt for more than 1 million years. The latest research also shows that each convergence of supercontinents is related to super mantle plumes rising under the plates. The real culprit of this mass extinction may be the super mantle plume.

Distribution of Large Igneous Provinces around the World

Mantle plumes come from the core-mantle boundary and bring about large-scale magmatic activity

Many species disappeared during the mass extinction

In the past, it was believed that the mass extinction at the end of the Permian lasted nearly 10 million years. Current research has found that the main extinction event occurred at the turn of the Permian and Triassic periods 250 million years ago. The end-Permian mass extinction that the academic community now believes refers to this event. And 10 million years before the turn of the Permian and Triassic periods, there was another extinction event at the turn of the Guadalupian and Lepingian periods 260 million years ago. At the turn of the Guadalupian and Lepingian periods, a super mantle plume gathered under southwestern China. After accumulating for tens of millions of years, when all the continents came together, this super mantle plume finally reached under the crust. The huge heat flow broke through the fragile crust and opened up countless volcanic channels at lightning speed. Basalt magma gushed out of the surface like a flood, and more than 250,000 square kilometers of land were covered by magma. South China, which is the most biologically diverse region, instantly turned into purgatory. With the emergence of super-large-scale volcanic activity, the sky was covered with thick smoke, the ocean gradually became acidic, everything was like doomsday, a large number of species went extinct, and only a few creatures that could endure the harsh environment survived. This giant magma activity formed the current Emeishan Large Igneous Province.

Emeishan Large Igneous Province

Finally, after five million years, the volcano began to calm down, the organisms began to recover slowly, and the environment was slowly recovering. But at the turn of the Permian and Triassic periods, something even more terrifying happened. Another super mantle plume gathered under Siberia. This time the mantle plume was larger and faster. The Siberian super mantle plume quickly impacted the crust, and a single crack could be as long as 50 kilometers. A large amount of basaltic magma gushed out of the crust from the cracks and volcanic necks, covering an area of ​​about 4 million square kilometers. The thickness of the basalt could reach 2,000 meters. This eruption lasted for more than 1 million years. Within 10 million years, two consecutive super mantle plumes made the biological world completely desperate, and the ecological environment of land and ocean entered a vicious cycle. It was difficult for organisms to endure the ecological environment full of miasma and poisonous water. Life seemed small and powerless in the face of the earth's wrath, and 95% of organisms went extinct.

The latest research results of Chinese scholars have found that large-scale acidic volcanism in South China is another major cause. Through the high content of copper, mercury and abnormal isotopes in the strata, it was found that large-scale volcanic activities around the Pan-Ocean and the Paleo-Tethys Ocean exported 1.9 billion tons of copper and several billion tons of sulfur dioxide to the continent, seriously affecting the marine and terrestrial ecosystems. The volcanoes also destroyed the terrestrial vegetation system. This disaster was earlier than most volcanoes in the Siberian Large Igneous Province and is likely to be the real cause of the mass extinction event. At present, the real cause of the end-Permian mass extinction is still a mystery.

Siberian flood basalt

The Permian period was a period of high incidence of mantle plumes. Mount Emei and Siberia are two super mantle plumes.

The horrific end-Permian extinction event

This mass extinction event originated deep inside the Earth and also affected the Earth's environment. Not only did it cause many organisms that had been active for 200 million years to disappear, but it also caused the Earth's environment to become devastated. But life did not end there. The surviving organisms seemed to have taken over the baton of a new era, continuously improving the Earth's environment generation after generation, and finally awakened the long-dormant Earth ecology millions of years after the mass extinction. By this time, time had already entered the Mesozoic Era, and a brand-new biological appearance was waiting for future exploration.

Triassic biological restoration map

The story of life continues. If you are interested, please stay tuned for the next issue. Triassic Period - Return of reptiles, a new era? Extinction again?

References:

[1] Wikipedia

[2] Britannica

[3] Shen Shuzhong, Zhang Hua. What caused the five mass extinction events? [J]. Science Bulletin, 2017, 62(11):17.

[4] Shen Shuzhong, Zhang Hua, Zhang Yichun, et al. Comprehensive stratigraphy and time framework of the Permian in China.

[5] Permian: The Creation of a Supercontinent – ​​Museum

[6]Ramsay JB, Wilga CD, Tapanila L, et al. Eating with a saw for a jaw: Functional morphology of the jaws and tooth-whorl inHelicoprion davisii[J]. Journal of Morphology, 2014.

[7]Wang, C., Mitchell, RN, et al., 2020, The role of megacontinents in the supercontinent cycle: Geology, v. 49, no. 4, p. 402-406.

[8]Zhang, H., Zhang, FF, et al., Planavsky, N., Shen, SZ*, 2021. Felsic volcanism as a factor driving the end-Permian mass extinction. Science Advances 7, eabh1390

The pictures are from Wikipedia, Pinterest, DeviantArt and some references

Editor: Wan Peng

Art Editor: Xu Hongxi

Proofreading: Wang Haibo Shenboheng

Source: Institute of Geology and Geophysics, Chinese Academy of Sciences