The history of the earth is a magnificent life course of 46 years, 4.6 billion years of stories are too many, and life has experienced too many twists and turns and magic from the emergence to the step by step to today. Maybe we will never know how likely life is to appear on a planet, sometimes we feel that it all comes from chance, sometimes we feel that it is all inevitable, sometimes it seems to be a miracle, and sometimes we realize that this is the natural end of the struggle of life. While we can learn about the events that have had a key impact over 4.6 billion years of history, we will never know which tiny events and the butterfly effect they triggered have revolutionized the course of life on Earth. But what we can be sure of is that in the long course of history, the course of life has never slowed down, it has resolutely moved from humble to great, from ancient times to the future, and it will certainly go from the earth to a wider sea of stars. So what we can do is to trace the glorious years of 4.6 billion years, explore the vicissitudes of life changes, and experience the twists and turns of fate.
The story begins 4,567 million years ago, when the sun was just born, and the gas and dust surrounding the young sun formed a protoplanetary disk, and the solid objects in the protoplanetary disk, which we call the number of starons, exceeded 100 trillion, and suddenly a historic event occurred, two of which violently collided and merged together, which is the beginning of everything today, and the course of the history of the solar system is changed in this way. In fact, 4.6 billion years later, the energy generated by the collision of stars and children is still stored in the form of geothermal energy in the earth's interior and becomes the driving force of mantle convection. The so-called mantle convection refers to the decrease in the density of hot rocks in the depths of the earth to produce an upward heat flow, while the cooled rock density becomes larger and settles into the mantle, and the mantle convection can transport and release heat from the earth's interior to the surface. The volume of the earth is relatively large, so it cools for a long time, and the heat generated when the radioactive material inside the earth is converted into other materials is also continuously released, all of which makes this process of heat release never end in a long historical period, and the earth is still not cooled down, still full of vitality and temperature.
Time went on, since the two starlets collided and merged, more and more starbets joined in, due to the large number of stars in the protoplanetary disk, so the collision and merger process is very frequent, and eventually a larger number of stars are formed, which is the protoplanet. Protoplanets also seem to adhere to the Matthew effect, and among the large number of protoplanets, one of the oval rocks is significantly larger than the others, which is the protoplanet that began to grow rapidly, which is also the Earth 4.56 billion years ago. At that time, the radius of the Earth was about 100 kilometers, only about 15% of the current size, and in the place of the impact of the larger star, the star and its surrounding material melted to form a magma pool, but because the Earth at this stage was still relatively small and the gravitational force was relatively weak, the energy generated by the collision could not form a magma ocean. So about the accretion of protoplanets, we can't help but wonder, in the original protoplanetary disk, large and small stones formed by the merger of star-child impacts must be numerous, so why in the end only Mercury, Venus, Mars and Earth, these rocky planets finally stood out? This is because the star child will become larger and larger after continuous collision and merger, and the gravitational force will become larger and larger, so that it has the ability to attract distant star children to get closer to itself and eventually annex, such a result is completely random, the earth is like this constantly attracting the surrounding star children closer, merging it into its own part and becoming larger and larger, and the gravitational force gradually becomes larger The earth will also swallow other small-sized protoplanets, gradually clearing its orbit, so the earth is formed by the collision of the protoplanets many times.
Other planets in the solar system grew up in the same way, but Earth's size was larger than Mars, Venus, and Mercury, which became a key turning point in determining The Earth's environment. For example, Mars has only 10.76% of the mass of Earth, so its gravitational pull is much smaller than that of Earth, which makes the atmosphere on Mars escape to space. The remaining atmosphere is very thin and cannot produce enough greenhouse effects, so it is very cold on Mars now, with an average temperature of only -43 °C. In such an environment, life on Earth is difficult to reproduce and evolve, so the Earth is really lucky, it has won the top spot in the race of collision and merger among countless protoplanets, which has given the current conditions for life on Earth to be created.
Time went on for 10 million years, to 4.55 billion years ago. At this time, the Earth was already large enough, and the gravitational force had reached a certain scale, and the star children continued to approach the Earth under the action of the Earth's gravity and hit the Earth more and more violently. After countless impacts, the Earth began to grow larger, at this time the Earth has reached 60% of the current diameter, as the Earth continues to grow, the gravitational force is also increasing, which leads to the acceleration of the movement of the star, so that the impact from the star is not only more violent, but also the frequency of the impact is accelerated. Under such conditions, the earth's magma ocean gradually formed, reaching hundreds of kilometers deep, and this period of history is also the only time in the history of the earth that the outside is hotter than the interior. Magma oceans are crucial to the development of the earth, when the molten iron in the magma composition is heavier, and deposited in the depths of the magma ocean, the hot iron melts the rocks below and continues to settle to the center of the earth, so that the internal structure of the earth such as the core and mantle begins to gradually form, at this time the earth is covered by the magma ocean, so there is no life, but it provides conditions for the formation of future life. Underneath the magmatic ocean, the Earth's interior differentiates into cores and mantles, and the creation of mantles and cores is closely related to the mantle convection that later led to continental drift and the birth of the Earth's magnetic field. At this time, the small fireball of the earth seems to have begun to resurrect after suffering the pain of rebirth, embarking on a difficult process of metamorphosis from a rock to a planet suitable for life.
Time went on, and another decisive event occurred at 4.533 trillion years ago. As we mentioned above, the surface of the Earth melts under the impact of the star, and some of this molten material is thrown into space. But the collision power of these stars is not strong enough. Scientists speculate that a Martian-sized object once flew toward Earth and slammed into it obliquely. The impact was unusually violent, causing a large amount of material from Earth to fly into the universe, forming a disk around the Earth. Although most of the material will eventually fall back to the Earth after cooling, some of the material will attract each other and converge close together, and begin to orbit the earth, which is the situation of the birth of the moon described in the "Great Collision Hypothesis", one of the theories of the birth of the moon. A very important piece of evidence now also points out that this view is the most reliable conjecture of the formation of the moon, that is, the material that makes up the moon is basically the same as that of the earth. So how important is the formation of the Moon to Earth? It can be said that this accidental event changed the history of the earth to a great extent. The great collision hypothesis holds that the great collision caused most of the water vapor on the earth to fly away and disappear, and the earth that lost water became very dry, but fortunately, the meteorite that hit the earth later continued to live the earth and provided conditions for the emergence of life. Some people may ask, wouldn't it be better if there was no big collision?
This is not the case, if the earth's water is retained, then coupled with the water that the meteorite later gave the earth, the earth is likely to be completely engulfed by the ocean, and terrestrial life may never be born. Of course, there is another hypothesis about the formation of the Moon, which is the "homology theory". The "homology theory" holds that the Moon was not blown out of the Earth, but formed simultaneously with the Earth in the protoplanetary disk and was eventually captured by the Earth's gravity, and the region that formed the Moon and the region that formed the Earth are very close to each other, which can also explain the same phenomenon that the Earth and the Moon are helpless. If this is the case, the influence of the Moon is still not negligible, because the amount of water is only a conjecture after all, and regardless of how the Moon was formed, we can be sure that without the Moon, the day on the Earth may become shorter, just as when the Earth was born, there were only 5 hours a day, and after the birth of the Moon, under the action of the tidal force between the Earth and the Moon, the Day of the Earth gradually became longer until it became what it is now. So does earth with an orbit time of 5 hours produce life? We don't know this, in short, it is not as good as it is now. Even if life is born, even if human beings are born, there must be no you and me.
In this way, the earth continued to struggle for itself, and by 3.8 billion years ago, the earth, a shelter born in a very low temperature space, finally deserved its name, forming an environment suitable for life. The inner part of the Earth becomes the core and mantle of the Earth, surrounded by oceans, atmospheres and the Earth's magnetic field. These elements perform their respective functions and are indispensable conditions for the birth of life. First of all, let's look at the core of the Earth, the core of the Earth is located in the center of the Earth, mainly composed of metallic elements such as iron, because the liquid iron in the Core of the Earth can flow, so the Earth magnetic field is formed around the Earth. The magnetic field line starts from the north magnetic pole of the earth into the south magnetic pole, because the particles from the sun are charged, so when they are close to the earth's magnetic field, they will change their trajectory and advance along the magnetic field, which makes the earth immune to the solar wind, and now the core is divided into the core and the outer core, which is maintained by the flow of liquid iron in the outer core. The mantle is a layer of rock located around the core of the Earth, and although it is solid rock, it is actually slowly convected through the way hot rock rises and cold rock settles. In this process, through hot spring vent passes and volcanoes, matter is generated as a source of energy for life activities. In addition, mantle convection also forms volcanic archipelagos, which gradually increase the land. In addition to the earth's interior being prepared for the creation of life, the environment on the earth's surface is also poised for development. First of all, the atmosphere is rich in greenhouse gases such as carbon dioxide, so although the sun was dimmer than it is now, the earth was still very warm, so that water could exist in liquid form without freezing. At the same time, the circulating ocean carries heat from the equator, which is easily heated by sunlight, to the poles that are difficult to heat, and the effect of heating the entire earth is realized. In addition, of course, the Earth's core, atmosphere, oceans and mantle have many functions, which are coordinated and work together to ensure an environment suitable for living organisms. In fact, in addition to the conditions on the earth, the conditions outside the earth also create a friendly environment for life, which is the newborn moon. Although Earth has been hit by a large number of meteorites in the early solar system, meteorite impacts have decreased during this period, which is exactly the hatred that the moon has pulled for us. Since there is no plate movement on the moon and the land is not eroded by wind and rain, there are still traces of past meteorite impact craters on the moon. Just as your current years are quiet, it is someone who carries the weight for you, so thank the moon.
In addition, the position of the earth in the solar system is also very nice, the distance between the planet and the sun directly determines whether there is liquid water on the planet, but also determines the size of the planet and the composition and content of the atmosphere. Everything on Earth is just right, and studies have shown that there were oceans on Mars among the planets of the solar system, but in the end it did not retain this luck, and until now, we do not know which other planet in the universe has the luck of Earth. Life has not lived up to everything that the earth has worked hard to get, fossils and other documents prove that the earliest life was born 3.5 billion to 4 billion years ago, that is to say, after the earth's environment has just been perfected, life can't wait to appear, so where did the earliest life appear? It is now accepted that life appeared on the seabed as early as 3.5 billion years ago, when there was almost no oxygen on the earth, the atmosphere was mainly composed of nitrogen and carbon dioxide, in addition to gases such as methane in the atmosphere, although the earth at this time had volcanic islands, it is estimated that there was no continent at that time. The earliest ancestors of human beings were prokaryotes living in the high temperature environment of the seabed.
3.5 billion years ago, the pitch-black seabed towered over many "chimneys" that erupted with black turbid hydrothermal fluids, which are rich in organic matter and hydrogen sulfide in China, and for organisms, organic matter is an indispensable delicacy for maintaining life, so from the perspective of nutrients, the conditions for life to completely cross the river here. So how did these "chimneys" come about? First of all, the seawater penetrates into the depth of several kilometers below the seabed, and will be heated to a maximum of 350 ° C by the hot basalt magma in the upper layer, which is a variety of chemical reactions between hot water and basalt, generating hydrogen ions, sulfide ions, methane, carbon dioxide and various metal ions, which can be used as a source of biological energy. After this, the hydrothermal liquid carries the material generated in the ground and rises sharply almost without any cooling, gushing out from the seabed, and due to the presence of high pressure on the seabed, the hydrothermal liquid, although far exceeding 100 ° C, does not boil. After the ejected material is mixed with the substance in the seawater, the temperature of the hydrothermal fluid decreases or the composition in the seawater reacts chemically again, forming black microparticles that look very much like black smoke. Because a large number of microparticles are deposited around the spray pass, the structure of the chimney is formed, and the height can even reach tens of meters.
Scientists now believe that the hot spring overflow is not only the residence of the common ancestor of living things, but also the birthplace of the earliest life that evolved due to the common ancestor. The common ancestor of living things based on simple organic matter in hydrothermal fluids generated complex organic matter such as DNA and proteins, and eventually gave birth to primitive life. Although the hydrothermal temperature in black chimneys can be as high as 350 ° C, complex organic matter such as DNA and proteins simply cannot withstand such high temperatures. However, there are usually white chimneys around the black chimneys, because the hot water rising from the ground mixes with the infiltrated seawater and undergoes a chemical reaction on the seabed, and the particles are deposited under the seabed and then spray white or transparent warm water into the sea, and the temperature of such white chimneys is generally between 20 ° C and 100 ° C. Therefore, organisms can grow and multiply under white chimneys. In addition, the interior of the black chimney wall is a sponge structure, where the hydrothermal fluid is also mixed with seawater to become warm water and seeps outward.
The temperature inside the sponge structure is relatively low, and various chemical reactions are also taking place in these places. Rich in substances such as hydrogen sulfide and methane that can be used as a source of biological energy, complex organic matter may also have the opportunity to form. In fact, until now, there are still a large number of microorganisms living in the chimney walls, which is an important basis for us to use this place as an important basis for the origin of life, so that we can understand why humans are so excited after discovering that there may be a similar hydrothermal fountain on Enceladus. But life will eventually leave the dark deep sea and head for a wider place.
But 800 million years have passed in the blink of an eye, and the environment on Earth has not changed so friendly, and at 2.7 billion years ago, the amount of oxygen in the atmosphere was only one part of 10 trillion, which is no different from no oxygen. There are volcanic islands and small continents on Earth, but the exact distribution is not yet very clear. If you could travel back 2.7 billion years you would hardly have imagined that this would have become our home. At that time, the earth's sky was red, hazy, and blurry, and even the ocean reflecting the color of the sky looked red. At that time, the atmosphere was filled with greenhouse gases such as methane and carbon dioxide, and the reason why the atmosphere appeared red was precisely because of the particles produced by the chemical reaction of methane in a large number of yards. Models of stellar evolution show that the Sun was dimmer then than it is now, and its ability to heat the Earth was relatively low. But thanks to powerful greenhouse gases such as carbon dioxide and methane, the earth has been able to maintain a warm environment, and prokaryotes that breathe anaerobically, that is, bacteria and archaea, have survived.
Over time, large-scale bacterial cyanobacteria have emerged on Earth, which can use carbon dioxide, water, and sunlight to generate their own components and release oxygen through photosynthesis. At the same time, bacteria have emerged on Earth that can break down oxygen to produce energy. Through the phagocytosis of bacteria, these two later form plant cells and animal cells. The oxygen emitted by cyanobacteria reacts with iron ions in seawater to form iron oxides and deposit it on the seafloor. In addition, oxygen reacts with methane in the atmosphere to reduce the amount of methane in the forehead. As a result, the number of particles produced by methane decreases, and the hazy and blurry sky begins to become blue and clear. More critically, photosynthesis not only reduces the amount of carbon dioxide in the atmosphere, but also increases the amount of oxygen in the atmosphere. After 500 million years of perseverance and breathing, cyanobacteria has finally completely changed the earth's environment. However, 2.2 billion years ago, the earth became colder and colder due to the drastic reduction in the amount of carbon dioxide caused by cyanobacteria. Earth entered the first Great Ice Age in history.
Another 100 million years passed, and the structure of single-celled organisms changed dramatically.
They had a nucleus wrapped in a membrane of DNA that recorded their genetic information, and for the first time on Earth, a creature with a nucleus was born, that is, eukaryotes. Although they were only the simplest single-celled organisms at the time, eukaryotes were more complex in structure and had various organs than their predecessors, the most important of which were naturally chloroplasts and mitochondria in organelles. So how do eukaryotes get mitochondria and chloroplasts? Before the advent of eukaryotes, there were only prokaryotes on Earth, and their structure was very simple, with parts such as DNA scattered inside cells. Some traces suggest that mitochondria and chloroplasts were once separate organisms, such as the presence of independent DNA inside the mitochondria. In 1967, american biologist Lynn Margulis proposed the famous intracellular symbiosis theory, that is, animal and plant cells, which evolved through phagocytes. This theory holds that bacteria were swallowed up by a type of archaea between 2 billion and 1 billion years ago, and that the bacteria that were swallowed up later, for unknown reasons, had the ability to use oxygen to break down organic matter and obtain energy. So archaea entrusted the efficient productivity of aerobic respiration to bacteria that devoured themselves. On the other hand, the bacteria that are swallowed are also very happy, because as long as they live in the body of ancient bacteria, they can get nutrients. In this way, bacteria and archaea began to love each other, mutually beneficial symbiosis. In the long-term symbiosis process, the two feel that cohabitation life is really good, simply do not do two endlessly into one, so this fusion of archaea and bacteria organisms, it evolved into animal cells, and the bacteria that were swallowed evolved into organelles that produce energy in cells - mitochondria. Now the role of mitochondria in animals is oxidative metabolism, which is the same as the role of engulfed bacteria in the past. After this, there were organisms that devoured cyanobacteria, and the phagocyanobacteria used photosynthesis to generate organic matter using light, inorganic matter and carbon dioxide, and finally archaea were simply integrated with the cyanobacteria swallowed by it, and there was a creature that could perform aerobic respiration and photosynthesis by the fusion of archaea and cyanobacteria, and this fusion organism later evolved into plant cells, and the cyanobacteria that was swallowed became chloroplasts. Now, we look at the role of chloroplasts, which is also in line with the role of cyanobacteria that was swallowed up in the past.
Time went on and on, the number of eukaryotes gradually increased, and the oxygen content in the atmosphere rose to a concentration of 1%. 900 million years ago, some scattered land finally floated together to form a supercontinent in the southern hemisphere, which is the Rhodinia supercontinent, the name Rhodonia is derived from the Russian language, the original meaning "hometown" or "mother tongue". In fact, regarding the distribution of continents, so far, scientists can only accurately copy 600 million years ago, the older the era, the more difficult it is to copy. Scientists also debate the details of how the Rhodinia supercontinent is distributed, and in general, geologists will piece together the land piece by piece like a puzzle based on the remaining address information from all over the world, so as to restore the continental distribution of each era. But the Rhodinia supercontinent is too old, and the drawings now made by Professor Li Zhengxiang of Curtin University in Australia and others are the most cited hypothetical maps. But no matter what the shape of the Rhodinia continent is, it is certain that on the Rhodinia continent, there were towering mountains in the area formed by the collision of supercontinents, but because there were no plants and other creatures at that time, the appearance of the continent was very monotonous, full of rocks and gravel, showing a desolate scene. Despite the desolation, active geological activity continues, preparing for the emergence of higher life. The vast land of the supercontinent is constantly eroded by wind and rain, resulting in the continuous flow of nutrients such as phosphate, which are needed by organisms, from the land into the seawater along the coast. Scientists now believe that this process is likely to be the driving force behind the sudden and massive outbreak of cambrian life in the shallow sea, during which a huge Ediacaran fauna appeared on Earth, a topic we will talk about later. So the name Rodinha is very appropriate, we don't know how much the continent before Rhodinia contributed to the explosion of life, but it is true to call the continent of Rhodinia the mother continent. However, the so-called First Nine Hidden Dragons should not be used, good things are more grinding, and now is not the time to see the dragon in the field. Before the Cambrian explosion of life, life on Earth will continue to lie dormant for a period of time, and it will also suffer a test of life and death.
About 650 million years ago, the oxygen content in the atmosphere has risen to about 2%, and the Rhodinia supercontinent is gradually splitting, but at this time, whether it is land or ocean, the entire earth is covered by thick ice, from space, the whole earth looks like a huge ice ball, so the earth at this time is also called "snowball earth", the average temperature is -40 °C, even the temperature on the equator is only -30 °C, and the thickness of the ice layer reaches more than one kilometer. Remnants of glacial sediments in the low-latitude tropics are evidence that earth has had a great ice age. If even the warmest parts of the planet are covered by glaciers, it wouldn't be surprising that the entire planet is covered with thick layers of ice. It can be said that the earth at that time from the surface, did not have any biological breath, scientists on the limestone analysis of the time also showed that the photosynthesis on the earth at that time was sharply reduced, oxygen content is also in a continuous reduction, which also means that the photosynthesis of the organisms at that time suffered a serious blow on the world. However, the creatures are still extremely tenacious, just in such a harsh environment, the process of self-struggle still has not stopped, some photosynthetic organisms that are sealed in the thick ice layer together with minerals, forming a black lumpy substance, in the freezing period they will be in a dormant state, but whenever there is sunlight in, the surrounding ice melts, they will wake up from the dormant state, begin to photosynthesis, so as to maintain life activities, and now there are such muffled and rich creatures under the Antarctic ice. In addition, organisms that do not photosynthesize can take shelters that are not covered by ice, such as hot springs around volcanoes or hot spring vents on the seabed. These places are warm and rich in nutrients, making these creatures lucky to escape the long ice age. In short, our ancestors must have been lucky enough to survive somewhere. Studies believe that the ancestors of humans originated from single-celled organisms that formed flagella, which is the closest single-celled organism to multicellular organisms, with elongated flagellar. In such a frozen and cold world, the creatures of that time must have suffered a huge blow, and the situation was extremely tragic. Although there is a lack of fossil and other related records to understand the scene at that time, it may be said that this global freezing is the largest extinction event in the history of the earth. But on the other hand, the Great Ice Age, 650 million years ago, was also a natural screening. Earth creatures may seem calm, even lifeless, but this is also the last calm before the storm.
Fast forward 20 million years, the oxygen content in the atmosphere has begun to increase, and the continent of Rhodinia continues its own path of division. 630 million years ago, there was a leap forward in the microbial world, with some single-celled organisms coming together to form a group or something else, and early multicellular organisms began to emerge. We know that all living things are made of cells, and our human beings are multicellular organisms made up of about 60 trillion cells, and at the same time, there are many kinds of one-cell organisms in the world, that is, single-celled organisms. So, how did a single-celled organism become a multicellular organism? This is uncertain and controversial. One hypothesis is that, but the population of cells that congregate, is the origin of multicellular organisms; the other hypothesis is that the nucleus divides and proliferates within the cell to form multinucleated cells, which then divide into multiple cells, that is, multicellular organisms, and most likely, both have occurred. Current research also believes that the evolution from single-cell to multicellular occurs independently in various organisms.
So according to the law of survival of the fittest in evolutionary theory, what is the survival advantage of multicellular organisms over single-celled organisms, and why do multicellular organisms appear? Danish geologist Donald Canfield proposed a hypothesis that about 600 million years ago, the increase in oxygen content in the ocean gave multicellular organisms that gathered together by chance to have a survival advantage, and may even directly lead to the emergence of multicellular organisms. The key is oxygen. On the one hand, oxygen is an indispensable element for breaking down nutrients and releasing energy; but on the other hand, oxygen may also hurt the cells themselves, so if the cells are huddled together to share oxygen, in addition to the outermost layer of cells exposed to oxygen, the inner layer of cells can safely avoid excess oxygen, so multicellular organisms appear. Or the multicellular organisms that already exist have a greater survival advantage. In addition, if the multicellular organisms from scratch have nothing to do with the increase in oxygen, they appeared very early, then the behavior of survival in groups not only reduces oxygen damage, but also with the help of the fact that oxygen increases, they can also use this opportunity to flourish rapidly. This is mainly because collagen binding to cells is very important, in order to form multicellular organisms, first need to produce similar collagen substances, but the production of collagen needs to consume a lot of energy, because oxygen in this period of rapid increase, collagen production has become easier, so more and more multicellular organisms have emerged.
Time has passed by now, the earth has gone through 4 billion years, all the preparations are ready, the biological explosion is ready, and a new earth is about to appear. If we think of the Earth from its creation to the present as 24 hours a day, it is already 9:03 p.m., or 560 million years ago. By this time the Earth had passed its coldest period, and the continent of Rodinya was gradually dividing into gondwana and a number of other slightly smaller continents. Although the ancestors of human beings were still extremely small at this time, single-celled organisms or single-celled animals, in short, very small, but the ocean is already a socialist change of heaven and prosperity, at this time the ocean can be described as the garden of living things, everywhere you can see the leisurely figure of marine life, Ediacara biota is a famous gang in this period. Because scientists found a large number of fossils from that time in the Ediacaran Hills region of southern Australia, the fossil group was named the "Ediacaran Biota". They housed their homes in the vast ocean around the supercontinent and enjoyed the benefits of communist society. The study suggests that these creatures have neither hard bones nor complex sensory organs, but rather a large group of soft, slimy soft-bodied creatures that are rarely aware of each other's existence and are unsuspecting of other creatures. They didn't know and didn't need to avoid strong enemies, because there were no so-called predators. The creatures that could not move on their own just waited like rabbits to filter and absorb the floating organic matter. Moving organisms crawl around the ocean floor, looking for bacteria in sediments for food.
Let's take a few representative creatures in the Edicaran biota, and basically have a general understanding of what kind of creatures were in this period, one is called Yuga worm, which is about 15 cm long, flattened, and the surface of the body is interlaced with stripes, which can be close to the seabed. While moving, it constantly devours nutrients in the sediment. The second representative creature is called Ernita worm, which resembles a green pocket, about 10 centimeters high, and also has interlaced structures on the surface of the body. Then there were two large ones, a creature called the Chahn Sea Pen, which was close to Kobe Bryant and was like a huge purple leaf on the ocean floor, not knowing where it went; the other was called the Dickenson Jellyfish, which could be imagined by this name, but much larger than our common jellyfish, up to nearly a meter, devouring nutrients from under the body. Of course, it also looks much more disgusting, if you throw one in your home, you can be disgusted to death without being scared to death. In addition, there are some trumpet comrades, such as three-point disc worms, kimbera worms, etc., everyone can Baidu by themselves, and here they will not introduce them one by one. However, the Ediacaran biota did not leave any descendants in the subsequent Cambrian explosion, but all went extinct. One might wonder if they could have evolved into other populations. Unfortunately, this situation can be basically ruled out, because in the body of the Edicaran biota, there is an interlaced structure, and this structure can not find any clues in any later organisms, and evolution cannot be erased so cleanly. The reasons for the extinction of the Ediacaran biota are unclear, but perhaps some persisted into the early Cambrian period, 540 million or so years ago, but there was still no glimpse of the Cambrian explosion of life.
The Cambrian period was 542 million to 488 million years ago, and by 510 million years ago, the climate was getting warmer and warmer, and the ancient continents were divided into three small continents, Lauren, Baltic and Siberian, and there was another large continent, or the above-mentioned Gondwana continent. During this period of vitality, the ocean is the main battlefield of life, in the ocean live many strange creatures, such as the most famous is the odd shrimp, the body length of up to 1 meter, is the cambrian largest creature, at the top of the food chain, is the earliest hegemon in the history of biology. In addition to the odd shrimp, other characteristic creatures include the Marl Trilobite that swims faster than anyone, a species of trilobite, the Obavin sea scorpion with five eyes and a specialized appendage for predation, the Psychedelic Wawasi worm, and the tragic Pika bug that is preyed everywhere. Studies believe that the organisms of this era cover almost all modern biological "phylums", that is, the phylum of the genus Phytopodidae. These creatures appeared about 520 million years ago, which can be described as a miracle in the history of life, which is the Cambrian explosion of life.
So why do various biota suddenly appear at the same time? A more powerful hypothesis is that from this period onwards, organisms for the first time grew eyes and could easily see each other, which led to a life explosion. So what's so important about growing eyes? Above, when we talked about the Ediacaran biota, we said that the creatures of that period could not perceive each other. But when the creature has eyes, the big guy can finally find each other, one buddy may find that the other buddy looks delicious, and the buddy who is watching finds that the other party is looking at himself and has bad intentions, it can also make two choices, one is to choose the route to escape, the second is to meet you hard, narrow road meet the brave to win, today I will target you. So it's easy to see how this seemingly insignificant change in other creatures brings about a drastic change, making the competition for survival between a creature becoming a predator or a prey even more brutal. Therefore, in order to survive the competition of the weak and the strong, the creatures began to evolve rapidly, and the appearance also changed explosively, and the strong muscles and strong bones or shells could help the creatures actively hunt down the prey they found, or escape from the hands of predators.
It can be said that the Cambrian is the era of the shell, a large number of animals with hard shells have emerged in this period, and the materials of the shell are also various, including calcium carbonate, calcium phosphate, silica, chitin, etc., which means that at that time, the various classes of organisms evolved the shell alone. During this period, our ancestors were also making a fortune in a low-key muffled voice, they were a group of 2-3 cm long fish without jaws, living in the shadow of other creatures, looking forward to making a big news one day. However, life in the water is not a long-term solution after all, on the other hand, in the face of the cruel competition for survival in the water, some animals have also begun the process of landing. So what about on land? What difficulties will the animals and plants face after landfall, and what kind of future awaits them? We'll leave these topics to next Friday, A Brief History of Life: The Age of Land.