{Earth}The origin and evolution of life on earth

To understand the origin and evolution of life on earth, one has to look at the universe. In a universe of more than 15 billion years, countless planets have formed and disenchanted. There may be hundreds of billions of galaxies like our own Milky Way. If you narrow it down to earth's Milky Way, which is like our sun, there are about 200 billion of them. Next to each sun, there are planets. How many earth-like environments in the universe could conceivably support life? So the idea that life is all over the universe is to be expected.

The origin of life has been discussed

The earth formed about 4.6 billion years ago. The story of the origin of life on earth has been changing for the past two or three decades, starting with small changes and now with bolder, wild ideas.

The dominant idea in the past was to explain the origin of life on earth in terms of "chemical evolution". Early thought was that life on earth began with small molecules, large molecules and polymers; Life begins with the making up of cells, the copying of genetic genes, and the division and reproduction of cells. But when exactly did this happen? What kind of cells are produced? There is still a big debate.

One idea is that life could have come from ice. When the surface of the ocean freezes, small organic molecules coalesce into large molecules in cracks in the ice crystals, and life begins. Another idea is that, under the influence of tides pulled by the moon, seawater evaporates, condenses organic molecules, and the rock surface catalyzes the aggregation of small molecules, and life begins. At the latest, puts forward the idea of about 1978 years, life should be started: hot pot bottom crack of hot water, more than 300 degrees Celsius, the highest in the seawater with many specific chemical molecules, the chemical composition and rock, not only the important part of the produced water, life could start from there.

Signs of life are everywhere

Chemical evolution has loosened in the past few years, and people are less confident. Seven summers ago, NASA announced that it had found signs of life on a Martian meteorite. It turned out that a rock picked up on the Antarctic ice by an American female scientist in 1984 was the 12th meteorite from Mars to be examined. Seeing the tiny shapes on the rocks gave NASA ideas that many biologists have come up with in the past 20 years.

What is it? In beitou, in Yellowstone, in hot springs where eggs can be boiled, live photosynthetic bacteria that are not only thermophilic but thermophilic. In addition, if you drill down to 3,000 meters, there is no sunlight, no organic nutrients, but also a lot of bacteria live there, they eat, sleep, reproduction, is a group of natural chemical molecules and REDOX reaction to obtain energy.

Other bacteria can wake up after sleeping in amber for 20 million years. Such scenes can be found in many places on earth. For example, shen yupei, a professor at the university of California, Los Angeles, found many ancient lotus seeds under the black soil in northeast China. After taking carbon-14 years, she found them lying underground in accordance with the order of tang, song, yuan, Ming and qing dynasties. If you take a file to file the skin, let the lotus seed absorb water, and then put it in the water for three days, it not only bud, but also can grow new lotus seedlings.

So it's not just bacteria that are hardy, other creatures are hardy, too. If life can survive extreme conditions such as high pressure, high heat, and high acidity, what reason is there to think that it cannot travel between stars? Is there any reason to think that they can't be spread from one planet to another?

Life began 3.9 billion years ago

When did these determined lives begin? The scientific record is constantly being revised, most recently to 3.9 billion years ago, when extraterrestrial meteors were still bombarding the earth furiously and life had already begun in that tumultuous age. This comes from some molecules of organic carbon compounds.

In cold Greenland, certain small grains of calcium phosphate contain dark organic matter. Although organic matter can be produced from nature and synthesized by biosynthesis, the ratio of carbon-12 to carbon-13 in the analysis indicates that the black matter was synthesized by biosynthesis. Because only life can disturb the ratio of carbon-12 to carbon-13. If this definition is correct, then, by the time calcium phosphate was formed, 3.9 billion years ago, those little gravel particles had already encaged the bacteria's molecules. If life had appeared more than 3.9 billion years ago, it could have happened more than once. Life on earth has been ravaged many times, and humans are the descendants of those who survived.

Important strategies in symbiotic evolution

Looking for evidence for traces of life? Stromatolites are a good helper. Because stromatolites are living stones, on the surface of which live bacteria photosynthesize. These bacteria, basking in the sun every day, secrete a gel that cements minerals in the water and actively deposits them. And the stone itself, little by little, grows layer by layer. The creatures that make stromatolites have, so to speak, changed the composition of the earth's air and determined the direction of life's evolution.

The earth, like other planets, had no oxygen when it was first formed, because it was a by-product of photosynthesis, and the first thing it did, as the oxygen grew and increased rapidly with the photosynthesizing organisms, was to rust the earth. Iron, the fourth largest element on earth, is soluble in water when reduced and is deposited as iron ore when oxidized. Most of the iron ore in today's steel mills is iron oxide deposited 2.5 billion years ago. That's right, two and a half billion years ago, the oxygen produced by stromatolites rusted away iron from the earth, and then it began to encroach on life in the atmosphere.

Our ancestral cells had a choice: go extinct or move to a place without oxygen. But the smart ancestral cells survived by living in a symbiosis with bacteria. Before that, there was no nucleus in the cell, and all the chemical reactions were mixed up in the cytoplasm. When ancestral cells ingested bacteria that had previously lived independently and used oxygen, they developed the ability to "put different reactions in different cellular organs," which both solved the problem of oxygen toxicity and enhanced the efficiency of metabolic coordination. When bacteria enter our ancestral cells, they can't be separated from us anymore. This is a symbiosis, a very important strategy in the evolution of life.

A round animal embryo

Between 600 and 800 million years ago, at least twice, maybe four or five times, the earth froze into a hockey puck. Almost all the water on the surface became ice, which was a severe test for life and killed off many.

This continued until 580 million years ago, when the earth warmed up and turned into a warm, shallow sea near the mainland province of guizhou. After two or three hundred million years, guizhou has gradually become a land. Forty million years ago, the Indian plate and Eurasian plate collision, squeezing, hog the green, the Tibetan plateau, and uplift the yunnan-guizhou plateau, so the accumulation in guizhou three or four thousand meters of rock and began to face tens of millions of years of weathering erosion, in the end, finally collapsed, revealing hidden in those warm shallow sea creatures record five hundred and eighty million years ago.

In weng 'an county, guizhou province, there is a 580-million-year-old stratum in which many granular structures smaller than millet are found. If you take them out and look at them with a magnifying glass, you can see the cracks in them. One cracks into two, four, eight, sixteen... What is it? Animal eggs and embryos! When viewed under an electron microscope, the structure of each cell can be clearly seen. After grinding into thin slices, the line between cells is also visible, and every nucleus is in, even the yolk structure is preserved.

What animal could have laid so many eggs in ancient times? At first, researchers ground stones into thin slices or picked out embryos and identified them one by one. Sometimes you crack them open and look inside. But with such exquisite fossils, any damage is a crime, and it seems that more advanced techniques will be needed to analyse the structure in the stone.

Non-destructive analysis research

Just next door to tsinghua university in hsinchu is the national synchrotron radiation research center. If the particles are added with very high energies, parallel, high-resolution x-rays can be derived, which can take pictures of fossils, hoping to show the fine three-dimensional structure inside the fossils. It turned out to be a good idea, so they visited synchrotron centers around the world to see who could do it better.

This type of nondestructive analysis has now been studied in X-ray microscopy at synchrotrons in the United States, Korea, Switzerland, and Taiwan. Implicit in these studies is a fascinating expectation: that in ten years' time, when American spacecraft bring back rocks from Mars, only a handful of people should have the chance to participate, and that those who can see the tiniest structures in the Martian rocks with non-destructive analysis will have the chance to take priority.

April day under the sea is very lively

Tens of thousands of animal embryos can be found in a rock as big as a fist in the weng 'an fossil layer. Is there such a scene on earth? It's all around us. Every year in April, the second night after the full moon, the corals under the kenting sea bottom will lay eggs, countless beautiful follicles, the moment covered with seawater; Not only coral, a lot of invertebrates are laying eggs, clam shells send a lot of sperm eggs out, sea urchins, starfish are doing this, April night, the sea head is very busy!

The same scene may have occurred 580 million years ago in weng 'an, April day, the second night after a full moon, when invertebrates in the ocean were releasing sperm and eggs in large Numbers. But then came the catastrophe, the mass of developing embryos, which were quickly killed, and washed to a nearby sea where there was a great deal of phosphoric acid and calcium, which in turn quickly turned the embryos into immortal stones.

Geologists have a habit of dividing the earth's history into two periods, one called the Precambrian, and the other beginning with the Cambrian, the first period of the Paleozoic era. For more than a century, the beginning of the Cambrian period (540 million years ago) has been attributed to the emergence of animals, but the weng 'an formation in guizhou province, where a large number of fossilized animal embryos were unearthed, predates the beginning of the Cambrian by 40 million years. Apparently, there were many complex animals on earth long before the Cambrian period.

Important organisms in the evolution of the haikou worm

Chengjiang county, 50 kilometers southeast of kunming on the mainland, also has a special formation. Five hundred and twenty million years ago, it was a warm, shallow sea, but somehow, every hundred years or so, there was a disaster nearby. As soon as disaster comes, a large number of fine dust, will quickly living in the shallow sea buried down; In a very short time, dehydrated and squashed, many organisms are squashed into flat fossils before they can be corrupted by bacteria, leaving all structural details on the rock. There is a large area full of such fossils, known as the chengjiang biota.

In the small town of haikou by the dianchi lake, researchers found more than 300 bugs, called haikou bugs, in an area of less than four square meters. Its muscles are segmted and it has the digestive tract, tail, anus and four pairs of gonads. More importantly, it has one of the characteristics of a chordate -- a soft, elastic structure.

The vertebrate trait is the notochord, which our ancestors, instead of wearing stiff armor, grew on their backs so they could cope with the world with flexibility. And because he chose wisdom over armor, he grew a brain. Notochord and brain are the biggest differences between invertebrates and vertebrates, and the haikou insect has both these two structures, which is considered to be a very important link in the process of biological evolution, and a typical transition from invertebrates to vertebrates.

The succession of volcanic eruptions ended the Paleozoic era

The Paleozoic era had many periods, and the end of each period represented a disaster; Every disaster is a time of extinction. Toward the end of the Paleozoic era, land masses gradually gathered, coastlines disappeared, and the central part of the land became desert. As a result, the earth became very dry, and some creatures became extinct because of the drought.

But one thing changed all that. By most accounts, what is now Siberia was the site of a series of volcanic eruptions 250 million years ago. The eruption was unspeakably large. Over an area of 2.5 million square kilometers, four kilometers of magma accumulated. How long did the lava last? No one knows, but there must be a lot of ash, blocking the sun; Spewing out a lot of sulfur oxide, refracting sunlight and cooling the earth; Spewing large quantities of poisonous gas; The sulfur oxide sprayed into the sky, water into sulfuric acid, fell into the ground into acid rain. As you can imagine, it was a catastrophe!

As a result, almost all life on land died, and more than two-thirds of the land's large animals disappeared; Less than 5% of life in the oceans survives; The ground after the disaster no longer contains the spores of cypresses and woodworkers, but the fungal spores that corrupt the world. Can you imagine that miserable time? The ground is covered with furry fungi that are rapidly decaying the remains of dead creatures. However, the crisis is also a turning point, and a lot of new organisms began to appear, the end of the Paleozoic, the beginning of the Mesozoic!

Insects, birds and dinosaurs are the main characters

What about the Mesozoic? Reptilian creatures fly to the sky and become pterodactyls; Into the sea, into the ichthyosaur. In the end, the incredibly large, 60-70 meter long, earth-shattering dinosaur becomes the main character. And the discovery of feathered dinosaur fossils in northeast China's liaoxi region has shocked the world, putting a pause in the 150-year debate over whether birds' ancestors may have been dinosaurs.

Back 124 million years ago, the western liaoning region was a large, swampy forest where flowers had evolved and insects and birds were chirping and thriving. According to people's experience of looking for fossils, birds flying in the sky are usually not easy to be preserved as fossils, but there are hundreds of species, tens of thousands of bird fossils, some exquisite specimens, every feather is in. There must have been frequent volcanic eruptions, each of which left layers of ash in the ground, some thick, some thin, with considerable frequency.

Imagine, for a moment, the eruption of a volcano, the ash, the rapid erosion of that ecological world, birds and animals frightened, scrambling to escape from the forest, desperately run to the water. Some birds, flying in the middle, were caught up by the ash and poisonous gases behind them, and fell down into the mud and into the ash. The fine powder of the ash seeps into every space of the bird's wing, and the feathers are preserved so completely that before the bacteria can break them down, the bird is fossilized. Feathered dinosaur fossils, presumably formed in the same way.

More than a dozen feathered dinosaurs have been found here since the first feathered dinosaur was discovered in 1996. But why hasn't it been found anywhere else in the world? Except for the different dinosaur species, it is the special geological conditions and burial conditions in the western liaoning region that make the feathers clearly preserved.

Flowering plants co-evolved with life

There is so much color on the earth, so many kinds of living things, can make such a diversity of the world, all thanks to the flowering of plants. The purpose of a plant's flowering is not to attract mates. Nectar and flowers are made for animals. Once the animals are attracted, they help to spread pollen and seeds.

The insects leave their eggs on the plants, the eggs hatch into caterpillars, and the caterpillars begin to eat the leaves