Earth Story: A Brief History of Life

Where do we come from?

Where are you?

Where to go?

These are the three soul-searching questions of philosophers.

However, scientists have the answer.

01

Life comes from a chemical reaction

Earth, one of the eight planets in the solar system, is the only planet with life in the known universe.

It was formed 4.6 billion years ago. Sorry, scientists are still arguing about how it was formed, so I can't tell you.

The oldest rock on Earth was formed 4 billion years ago and is found on a small island in the Acasta River in the Northwest Territories of Canada. It is called Acasta Gneiss.

The oldest rock in my country is granite near Anshan, Liaoning Province, which was formed about 3.8 billion years ago.

▲The oldest rock found on Earth - Acasta gneiss. The picture comes from the Internet, please delete if it infringes

When and how did life originate? Such a complex question is naturally answered by philosophers first.

Engels said: "The origin of life must be achieved through chemical means." Many scientists also believe in the chemical evolution view of the origin of life, that is, under the conditions of the primitive earth, inorganic matter can be transformed into organic matter, and organic matter can develop into biological macromolecules and multi-molecular systems until the primitive life form evolves.

But these are just theoretical speculations. Who can prove it? That is the Miller experiment.

The famous Miller experiment was completed in 1953 by SLMiller, a graduate student at the University of Chicago, under the guidance of his mentor HCUrey. Miller assumed that at the beginning of life, there were only cyanide, ammonia and water vapor in the atmosphere, and no oxygen. When he put these gases into a simulated atmosphere and detonated them with electricity, he found that some proteins were produced, and proteins are the form of life.

Miller's experiment proved that humans most likely originated from a chemical reaction, from inorganic to organic.

▲Miller–Urey experiment is an experiment that simulates the chemical evolution process of the origin of life by producing organic matter (especially amino acids) through thunder and lightning in the reducing atmosphere of the primitive Earth. It was completed in 1953 by SLMiller, a graduate student at the University of Chicago, under the guidance of his mentor HCUrey, hence the name. Image from the Internet, please delete if infringed

So what can we use to prove the existence and evolution of life? Fossils are the key to unlocking the evolution of life.

After the death of organisms, their remains or relics will be preserved in rocks under appropriate conditions. We call them fossils. The rock layers formed in geological history are like a chronicle book. The evolutionary history of the earth's organisms is deeply buried in these rocks. The older the fossils, the more they are preserved at the bottom of the rock layer.

▲Fossils buried in rocks can prove the existence of life on Earth, as well as their appearance and living conditions on Earth. The following figure is a schematic diagram of fossil formation

02

Stromatolite Age

3.5 billion years ago, Earth began to nurture life, which we today define as organisms.

After the formation of the earth, primitive life was nurtured in the ocean. The first life forms were lower bacteria and single-cell algae. In the early oceans of the earth, there lived a kind of cyanobacteria that could carry out photosynthesis. Through photosynthesis, cyanobacteria brought oxygen to the ocean, and oxygen is the basis for the production and reproduction of other organisms. The emergence of cyanobacteria is of great significance to the evolution and development of the entire biological world.

Stromatolites are fossils formed by algae binding and precipitating calcium and magnesium carbonates and their debris particles in seawater during their life activities. So far, the oldest stromatolites we have discovered come from Western Australia. The Earth once entered the stromatolite era.

The emergence of cyanobacteria marked the beginning of plant photosynthesis on Earth. As a result, the Earth's environment began to change, and the original reducing atmosphere and water bodies transformed into an oxidizing environment.

However, for cyanobacteria, environmental changes were a tragedy, because the large amount of oxygen produced by cyanobacteria eventually led to the extinction of cyanobacteria, while other life was able to develop rapidly. After that, the "Cambrian Explosion" came, which was the first explosion of life on Earth and ushered in the Phanerozoic Eon.

▲Stromatolite fossils discovered in Shennongjia World Geopark, Photo by Li Zhongdong

03

Age of Invertebrates

The earliest life forms were prokaryotes, which took 1.5 billion years to evolve into eukaryotes, and another 300 million years before multicellular algae appeared. With the emergence of eukaryotes, animals and plants began to differentiate and develop.

The emergence of animals has formed a new three-pole ecosystem. Green plants (eukaryotic plants and prokaryotic cyanobacteria) produce food through chlorophyll photosynthesis and are producers in nature; bacteria and fungi are decomposers in nature; and animals are consumers in nature.

700 million years ago, the Ediacaran biota appeared. It was first discovered in the Ediacaran Formation in southern Australia. It is mainly composed of jellyfish, seabranches, annelids and a small number of arthropods of coelenterates, as well as some difficult fossils whose classification positions are uncertain. They may represent groups that appeared briefly in geological history and quickly became extinct.

The Ediacaran Biota is the oldest known invertebrate group on Earth, and the Weng'an Biota in Guizhou, China is a typical representative of the Ediacaran Biota in China.

▲The Ediacaran fauna is located in the Ediacaran region of southern Australia. It is a large group of soft-bodied multicellular invertebrates that lived in the Precambrian period 565-543 million years ago. The following picture is an imaginary picture of the Ediacaran biota, from the Internet, please delete if it infringes

550 million years ago, the Earth entered the Age of Invertebrates. The period from the Precambrian to the early Paleozoic Era (about 550 million years ago) is known as the "Age of Marine Invertebrates" in the history of biological development. During this period, invertebrates flourished, including more than 20 major categories, and in the early Cambrian period 550 million years ago, a large number of animals developed "explosively".

In the oceans at that time, there were not only protozoa, but also various classes of metazoa, some of which floated in the water, some were fixed to the seabed, and some crawled on the seabed, a thriving scene.

Because seawater is rich in calcium, the earliest small shelled animals with calcium hard shells appeared, including soft-tongued snails, monoplacophores, gastropods, brachiopods, etc., which led to a sudden increase in the number of fossils preserved in the Cambrian period.

Among them, trilobites evolved rapidly, had obvious ecological differentiation, and were distributed throughout the entire oceans of the world. They had an absolute advantage in the animal kingdom, so the Cambrian period is called the "trilobite age."

The Yunnan Chengjiang Biota, named after Chengjiang County near Fuxian Lake in Yunnan, is the oldest and best-preserved soft-bodied fossil group discovered in the world. It includes more than 40 categories and more than 100 species, including sponges, cnidarians, mollusks, arthropods, etc.

▲The Chengjiang Biota is located near Maotian Mountain in Chengjiang, Yunnan, my country. It vividly reproduces the magnificent landscape of marine life 530 million years ago and the primitive characteristics of living animals. It not only provides scientific facts for the Cambrian explosion of life, but also poses a major challenge to Darwin's theory of gradual evolution. Image/Zhao Fangchen et al., 2012)

04

Fish appear

In the Cambrian period, invertebrates and vertebrates began to diverge, and 90% of the categories in the modern animal kingdom can find close relatives in the Cambrian fauna.

Fish began to appear in the Ordovician period about 480 million years ago, developed in the Silurian period (440-410 million years ago), and flourished in the Devonian period (410-360 million years ago). Therefore, the Silurian-Devonian period is also called the "Age of Fishes".

Fish are the lowest class of vertebrates, but at that time they were the highest class of animals on Earth.

▲Found in the Silurian strata of Xiushan, Chongqing, the miniature Border Town fish fossil, which is about 423 million years old and well-preserved jawed fish. The fossil is only 2 cm long, and the whole fish may have been only about 4 cm long when alive. Photo/CCTV News

05

Bio Login

With the large-scale sea retreat in the Silurian period (440-410 million years ago), the land area on the Earth's surface gradually expanded, preparing the way for the landing of organisms.

400 million years ago, life moved from the ocean to land, and the first to complete the landing were plants. In the late Silurian period 400 million years ago, with the gradual expansion of land and the continuous changes in the environment, many algae plants living in coastal or shallow sea tidal zones began to adapt to the new living environment. Some green algae gradually strengthened their sporophytes, which was conducive to the variation function of the terrestrial environment, and slowly developed towards land, producing terrestrial plants represented by naked ferns, becoming the real "pioneers" on land.

Ever since the naked ferns came onto land, the earth has changed from a barren appearance to a green one, and has begun to be full of vitality.

The emergence of naked ferns was a huge leap in the history of plants. The Earth began to produce more and more advanced terrestrial plants, and the terrestrial environment became more and more complex and diverse.

▲The naked fern is the oldest extinct terrestrial plant of the family Pteridaceae. It appeared in the late Silurian (or Early Devonian) strata about 400 million years ago. Its organs were initially differentiated to adapt to the terrestrial environment. It was a pioneer in the transition from the ocean to the land. The picture comes from the Internet. Please delete if it infringes.

After the organisms landed, it took them 200 million years to complete their occupation of the continent, forming a terrestrial natural geographical environment dominated by terrestrial plants and vertebrates.

In the Devonian period, about 410-360 million years ago, forests only existed on the coast. They were mainly composed of naked ferns, which were less than 1 meter tall, had no true leaves and roots, and reproduced by spores.

By the Carboniferous period, about 360-290 million years ago, land plants had developed into perennial trees, 20-30 meters tall.

By the late Permian period (290 million years ago), gymnosperms dominated, conifers and cycads flourished, and forests moved further inland due to their reliance on pollen dispersal.

After the development of terrestrial plants, insects that have a close relationship with plants multiplied in large numbers. They are interdependent, mutually restrictive, and develop in parallel.

▲At the end of the Paleozoic Era, gymnosperms dominated and forests began to cover the earth's surface. The picture comes from the Internet, please delete if it infringes

Insects became the earliest "pilots" on Earth.

The earliest insects were the most primitive wingless types. Fossils of this type first appeared in the Devonian Period. The earliest known winged insects appeared in the Carboniferous Period. The most prosperous insects at that time were the now extinct ancient net-winged insects. The Permian insect fauna underwent significant changes, the Orthoptera were significantly reduced, and many modern types began to appear.

After insects came ashore, vertebrates also prepared for landing, first of all to solve the problem of breathing and movement. Crossopterygians already had primitive lungs and fleshy paired fins that allowed them to crawl on the ground. They came ashore in the Late Devonian and were the earliest type of terrestrial vertebrates.

The earliest representative of amphibians, the labyrinthid ichthyosaurs found in Greenland and North America during the Late Devonian, are intermediate types that clearly represent the transition from lobe-finned fish to amphibians. The Carboniferous-Permian period was the most prosperous period for amphibians and is known as the "Age of Amphibians".

The remaining modern amphibians include salamanders, frogs, etc.

▲Ichthyostega is the earliest amphibian known to us. Although it has the trunk, legs and toes of a terrestrial animal, its head still looks like a fish, and its tail is similar to the caudal fin of a fish. This shows that the ancestor of Ichthyostega was a fish. The picture comes from the Internet, please delete if it infringes.

06

The Age of Dinosaurs: Dominated the Earth for 150 Million Years

About 200 million years ago, dinosaurs arrived and made a high-profile appearance. Reptiles, represented by dinosaurs, were the dominant vertebrates on Earth during the Mesozoic Era, so the Mesozoic Era is called the "Age of Reptiles" or the "Age of Dragons". Various giant, large, and small dinosaurs, ichthyosaurs, pterosaurs, and sea dragons were active on land, in the air, and in the sea.

The Zigong Jurassic Dinosaur Biota is the most typical representative of the "Mesozoic Reptile Age", burying the richest dinosaur fossil group in China, with many species, large numbers and complete preservation.

65 million years ago, after dominating the Earth for 160 million years, dinosaurs suddenly became extinct, leaving behind countless skeletons, traces of life, and various speculations about their extinction.

▲The Zigong Dinosaur Fossil Site is one of the most important paleontological fossil sites in the world. More than 200 dinosaurs and other vertebrates and tens of thousands of fossil specimens have been obtained, from which 23 genera and 27 species of fish, amphibians, turtles, crocodiles, pterosaurs, mammal-like reptiles, etc. have been identified, including 14 new genera and 24 new species. Photo/Zigong Dinosaur Museum

▲A 165 million-year-old dinosaur footprint fossil wall in the Turpan Basin in Xinjiang. The rock wall where the footprints appeared is 33 meters long, with more than 150 convex footprints. The picture below shows a dinosaur skin imprint fossil and a scratch fossil on the fossil wall. Photo/Zigong Dinosaur Museum

Are dinosaurs really dead? However, many scientists believe that dinosaurs are not really extinct, but are still living on Earth in a different form: birds.

The emergence of birds is a major leap in the history of vertebrate evolution. The earliest fossil representative of birds is Archaeopteryx from the Late Jurassic in Germany. In 1996, the "Sinosaur Bird" in Liaoning, northern China was initially thought to be a primitive bird, but was later confirmed by scientists to be a small carnivorous dinosaur.

The Jehol Biota in Liaoning Province provides a lot of evidence for scientists' conjecture. A large number of feathered dinosaurs (Sinosaurornis, Caudipteryx and Sinornithosaurus), primitive birds (such as Cathaysornis, Confuciusornis and Protoparis), and rare fossils have been discovered one after another. These have made more and more people believe that there is a kind of dinosaur that is still flying in the sky.

▲Sinosaurus lived in the Early Cretaceous 140 million years ago. Its fossils were found in the Jehol Biota in western Liaoning, China in 1996. It was initially thought to be a primitive bird and named "Sinosaurus", but later scientists confirmed it to be a small carnivorous dinosaur. The video is from the Internet, please delete if it infringes.

07

The World of Flowers, Birds and Beasts: Colorful Earth

The Mesozoic Era was the world of gymnosperms, but it had already begun to give birth to angiosperms.

Angiosperms appeared in the late Early Cretaceous 100 million years ago, quickly multiplied in the Middle and Late Cretaceous, and flourished extremely in the Cenozoic Era, replacing gymnosperms to become the most advanced group in the plant kingdom and ushering in the angiosperm era.

The rapid development and wider geographical distribution of angiosperms provided abundant food resources for the animal kingdom that depended on plants, and promoted the great development of insects, birds and mammals. Human life is also closely related to the development of angiosperms, and the emergence of a large number of flowering plants has made the earth colorful.

Entering the Cenozoic Era, continental drift, climate zoning and temperature changes have had a profound impact on the evolution, development and ecological environment of life. Mammals have rapidly multiplied, occupying various ecological areas before reptiles and becoming the new rulers of the earth.

On the mainland and islands, there are various birds flying that are close to their modern appearance.

Birds and mammals developed from reptiles with cold body temperature to warm body temperature. In particular, mammals developed from oviparous to viviparous and lactating, which was another step forward for the emergence of humans.

▲The mammoth, once the largest mammal on Earth, became extinct about 10,000 years ago. The picture comes from the Internet, please delete if it infringes

08

The human world

About 50 million years ago, primates evolved rapidly and differentiated into higher primates.

Around 30 million years ago, the earliest ape appeared, followed by Aegypti ape, Dryopithecus, and Proconsulpithecus. After that, two transitional apes appeared, Ramapithecus and Australopithecus ape.

Finally, 2.5 million years ago, a species appeared on Earth, which we call "human beings".

▲Some bones and skull fragments found by Raymond Dart in South Africa in 1924, named "Taung Infants"丨wikipedia.org.

They come from two Australopithecus species, dating back about 2.6-2.1 million years. The following picture is a reconstruction of an Australopithecus mother and her baby in Africa | Jose Garcia and Renaud Joannes-Boyau. The picture comes from the Internet, please delete if it infringes

Homo habilis evolved from a branch of Australopithecus and first appeared on the east coast of Africa. It was able to make and use tools and was the earliest human.

Homo habilis and Homo erectus once coexisted for a period of time, but at the beginning of the Paleolithic Age, after hundreds of thousands of years of evolution, Homo habilis was eventually replaced by a new species of human, Homo erectus, and died out.

Homo erectus first appeared in Africa, knew how to use fire, began to use symbols and basic language, and was able to use more sophisticated tools, which is called the Acheulean culture.

The earliest Homo erectus appeared 1.7 million years ago. About 1 million years ago, Homo erectus began to migrate, leaving Africa and expanding to all parts of the world. They were distributed in Europe, Asia, and Africa. For example, Heidelberg Man, Java Man, and Peking Man all belonged to Homo erectus.

About 800,000 years ago, Homo erectus arrived in what is now Spain and became the earliest Europeans. About 200,000 years ago, Homo erectus in Eurasia and Africa gradually disappeared and was replaced by a new species of humans, Homo sapiens, from Africa.

▲In 1929, Chinese archaeologist Pei Wenzhong discovered the first complete skull fossil in a cave on Dragon Bone Hill in Zhoukoudian, Beijing. They lived about 700,000 to 200,000 years ago, and still retained some characteristics of apes, but their hands and feet had obvious division of labor, they could make and use tools, and they could use natural fire. The picture comes from the Internet, please delete if it infringes.

Early Homo sapiens lived between 30,000 and 250,000 years ago. They originated in Africa during the Middle Paleolithic period and later expanded to the low and middle latitudes of Europe, Asia and Africa (except the Americas). This was the second time humans left Africa. Dali people, Maba people, Dingcun people, Xujiayao people, and Neanderthals all belonged to the early Homo sapiens.

Neanderthals, close relatives of the ancestors of modern Europeans, dominated Europe, western Asia, and northern Africa starting about 120,000 years ago, but suddenly disappeared about 30,000 years ago, and not only Neanderthals, but all early Homo sapiens became extinct.

Whether they failed in the survival competition with the late Homo sapiens who left Africa for the third time, or because they were unable to adapt to the cold of the Ice Age, remains a mystery.

▲Human evolution diagram, Homo erectus and Homo sapiens are the two major branches of the genus Homo. (Reference: Li Hui (2013) Genetics Reconstruction of the Hominidae Lineage. Re-understanding the Human Evolutionary Process from Genes. Modern Anthropology Newsletter 7:1-11). The picture comes from the Internet, please delete if it infringes.

Late Homo sapiens, lived about 10,000 to 50,000 years ago, was able to make fire artificially, lived in a matriarchal clan commune, belonged to the late Paleolithic period, and was the ancestor of modern humans.

The Shangdingdong people, Hetao people, Liujiang people, Qilinshan people, and Zhiyu people belong to the late Homo sapiens. It is generally believed that they came from Africa, arrived in Australia about 50,000 years ago, arrived in Asia 30,000 years ago, and arrived in America 12,000 years ago (according to records). They eventually differentiated and formed modern races such as yellow, white, black and brown, and are widely distributed all over the world.

It is still unknown whether the extinction of mammoths and saber-toothed tigers during their lifetime was their "masterpiece".

▲

09

What are humans? A new species? A visitor to Earth?

Modern humans and technology have become the dominant forces on earth.

Steel and cement replaced soil and wood, and cars, mobile phones, and robots were invented. By damming rivers, reclaiming land from the sea, breaking through the atmosphere, and extending their tentacles to the sky, humans became the true rulers of the earth, and had no natural enemies.

What is a human being? There are still many unsolved mysteries in the theory of human evolution.

For example, why can't we find the key fossils of human evolution? Why did humans lose their hair that protects against cold?

Scientists' research shows that the speed of human evolution has been accelerating over the past 40,000 years, especially in the last 5,000 years, when the speed of evolution is 100 times faster than before.

▲Human evolution diagram. The picture comes from the Internet, please delete if it infringes

Thoughts, language, the ability to wield tools, the ambition to conquer, and boundless desires, these are the characteristics that distinguish humans from other animals. Humans and animals seem to be taking completely different paths.

Nietzsche divided human desires into desire for power, appetite, and sexual desire, and these three desires of humans are completely different from those of animals.

Only humans have the desire to rule the world. Even the most powerful lion king can only lead his family to defend his territory. According to research, a lion group has no more than 20 lions and a territory of no more than tens of square kilometers.

Appetite: For animals, food is survival, and only survival. Many animals only go out to look for food when they are hungry, but humans have an endless pursuit of material things, far exceeding their needs.

Sexual desire, only humans have sexual desire at any time, and it is not for the purpose of reproduction. Animals only mate during the estrus and breeding season, and do not have this preference at other times. Some people call humans' unrestrained sexual behavior "animal desire", which is the biggest misunderstanding of animals.

Dinosaurs evolved for 150 million years and remained dinosaurs, but humans took only 2.5 million to become the rulers of the earth. Now that humans have landed on Mars, when the nuclear weapons invented by humans are enough to destroy the earth several times, when humans are enslaved by "technology", the smartest monkeys have only learned to use stones to crack nuts. Did we really evolve?

Is it possible that humans are an evolutionary accident? Or are we the alien species?

▲Neanderthal woman and Homo sapiens woman. Advanced technology enabled Homo sapiens to defeat Neanderthals and eventually stand at the top of the earth's biological world. The picture comes from the Internet, please delete if it infringes

10

What will happen to the Earth if humans disappear?

The Earth has existed for 4.6 billion years, and life has existed for 3.5 billion years. The history of mankind is less than one thousandth of the history of the Earth. If the history of the Earth is regarded as a day, the existence of mankind is only 50 seconds. Therefore, we are not only a new species on Earth, but we will also be a passing visitor on Earth...

Human beings will eventually disappear, and no one knows how long humans can stay on Earth. So what will happen to the Earth after humans disappear?

The United States once made a science fiction film called "Earth After Humanity Disappears". The film predicts that after humans disappear, all buildings will collapse within 1,000 years, and all civilizations will disappear within 20,000 years. After 50,000 years, all human remains on Earth will become archaeological traces that are difficult to trace, and within 200,000 years, all traces of humans will disappear, as if humans had never appeared...

The conclusion is cruel: the disappearance of human beings may be a disaster for civilization, but for this planet that has existed for 4.6 billion years, it is nothing.

-END-

Part of this article is based on Li Zhongdong’s speech “Walking in Billions of Years of Time” at the “Jinsha Forum” hosted by the Publicity Department of the CPC Chengdu Municipal Committee on October 13, 2018.

By Li Zhongdong

Editor | Lao Xia

Pictures丨From the Internet, etc.

Source: Xiake Geography