Dear passengers, please take your luggage, line up and get on the train. The train No. 233 circumnavigating the lithosphere is about to depart. We will pass through the crust and mantle, enjoy the scenery along the way-the rocks, and listen to their stories. I wish you a pleasant journey.
Stone shapes the earth
4.5 billion years ago, the earth was still a vast ocean. At that time, there was only one kind of rock-basalt. Basalt is an ore with many potholes, usually black. It is the “cell” of the ocean and constitutes most of the ocean crust in the world. Oceanic earthquakes and submarine volcanic eruptions “bred” basalt, and high-temperature liquid mantle magma “breaks out of the soil” and cooled in the ocean to form basalt. When the water and carbon dioxide in the rock are “driven” out by the high temperature, it will leave pits in the basalt.
Basalt is supposed to be the oldest rock on earth, but the oldest basalt that can be found is only 200 million years old. It was dug in the South China Sea by a team from Tongji University in China. In fact, basalt is far more “old” than this, but when they come to the crust, they will “transform” into other types of rocks, so the age of basalt itself is difficult to determine. Its other brothers, the rocks that came from the mantle to the crust like it, also “remade” and “reborn” in this way.
Andesite is an igneous rock formed by small crystals, usually light to dark gray. Andesite is formed by magma erupted by volcanoes after plate collision. It can be seen everywhere in the crust of the continent and can be said to be the “cell” of the land. Based on this, geologists proposed a way for continental crust to “grow up”: the temperature of lava from volcanic eruption is higher than that of cooled basalt, and the density is lower than that of oceanic crust, so these lavas will not sink into the mantle, nor enter the ocean, and cool down. Later, andesite formed and accumulated on the mainland. Slowly, the continent became bigger and bigger. The Andes in South America is the place with the most andesite in the world, and they are 170 million years old.
Granite is a kind of black, white, gray, rice and other dark mixed ore. Granite is also a kind of rock all over the world, but it is not the product of volcanic eruption, nor is it related to plate collision. Its formation process is very “mild.” Where the crust is relatively thin or there are cracks, the mantle magma will “see the cracks”. This magma merges with the original andesite of the crust to form granite. The age of granite is difficult to determine because it is easy to metamorphose into other types of rocks. It is generally believed that the average age of granite is 300 million years old.
Diorite is a kind of rock with black and white particles, which looks a lot like crushed Oreo cookies. Diorite is the product of the “combination” of basalt and granite. Part of the mantle magma that “breaks out of the earth” in the ocean cools to form basalt, and the other part of the magma rises faster than it cools and finally “rushes out” The ocean enters the granitic rock layer of the continental plate. The high-temperature magma melts the granite and mixes with the granite magma, thus producing a kind of rock between basalt and granite-diorite. Because this kind of “scud” magma can be encountered but not sought, diorite is very rare in the world, and only volcanic groups or volcanic arc areas can find some of them. The age of diorite is similar to that of granite.
Earth changes rocks
Looking at the rocks that shape the earth, do you think the colors are too monotonous? Presumably the earth also thought that such a monotonous rock could not highlight its beauty, so it did it by itself and “dressed up”.
Quartzite is usually white or gray, mainly or entirely composed of quartz (silica). Quartzite is the “skin” of a mountain. During the uplift of the mountain, erosion will scrape away all the ore particles in the rock except for quartz, or the small stream on the mountain will gather the quartz particles together and compact it into quartzite. It is precisely because quartzite has experienced “big waves and sand washing” during its birth, so it is exceptionally “strong”. Even if the entire mountain is “blown” flat, quartzite is still the last rock left. The oldest quartzite found so far was found in the Altai region of Xinjiang. It is 2.6 billion years old.
Next, we see a piece of pink rock, which is composed of very coarse red and brown particles, the main components are silicon oxide and iron oxide, which is feldspar sandstone. Because feldspar sandstone melts into clay as soon as it encounters water, generally where it forms a rock formation, we can estimate that this place has been dry for many years. The oldest feldspar sandstone found so far is located in the central part of Colorado, USA, and was formed in the Triassic period 300 million years ago.
Gneiss is a kind of stone with stripes, usually black on white background or black on brown background. Gneiss is the “heart” of a mountain. When a plate collides to produce a mountain, the huge pressure deep in the mountain will squeeze the rock into a gneiss. After millions of years, when the mountain is eroded and flattened by wind and rain, its “heart” gneiss will be excavated by us. Gneiss is the oldest rock “made by the earth” found so far. The gneiss found in the Asta River Basin in northern Canada is more than 4 billion years old.
Kimberlite is a kind of rock that is mostly gray-black and dark green, but regardless of its appearance, it is the “mother” of diamonds. If the high-speed magma erupted by the volcano fails to follow the large forces to walk along the “Kangzhuang Avenue”, and the road is blocked after the magma in front cools, it can only reach the surface through the narrow and narrow lava. Kimberlite. Narrow roads will put more pressure on the magma, which is conducive to the formation of diamonds, so diamonds are often “bred” in Kimberlite. The average age of kimberlites discovered today is about 480 million years old.
The ophiolite looks like a snake skin, showing a black and green color, with a waxy luster. Ophiolite usually appears on the edge of a continent or island, that is, the “end point” of the ocean. Geologists can use the distribution of ophiolite to infer the boundary between the continent and the ocean long ago. When a continental plate collides with an oceanic plate or an earthquake occurs inside the ocean, the continent will expand, stacking and squeezing between rocks will form ophiolite, and even some marine life that is too late to escape will be “sealed” in the snake In the green rock. In North China, geologists have found the oldest ophiolite with an age of approximately 3.1 billion years.
Eclogite is a very beautiful rock, often mixed with bright red, green or blue colors. We can usually see it deep in the ocean, because it can only be formed under high temperature and high pressure. 170 million years ago, there was a collision between the Pacific plate and the American plate, and the Pacific plate was pressed under the American continental plate. A “hot” spark burst out where the two plates collided. The temperature was as high as 400°C to 500°C and the pressure was about 20,000 standard atmospheres. In this environment, a variety of different stones are compressed together to form eclogite.
Creatures participate in transforming rocks
Not only the earth, but the inhabitants of the earth-living things have also participated in the action of decorating the earth.
In early 2017, scientists at University College London discovered fossils of tubular microorganisms in red hematite in Quebec, Canada. These microorganisms are only one-tenth the thickness of human hair, and survive by metabolizing iron. Researchers believe that they are at least 3.7 billion years old, and may even be more than 4 billion years old. They are at least at least older than the oldest fossil ever discovered, the 3.5 billion-year-old cyanobacteria found in stromatolites in Australia. 200 million years old, but this view has not yet been widely recognized. But in any case, the history of life on earth is still much longer than we thought.
Banded iron ore
What we see now is a sandwich-like banded iron ore with three colors of black, red and white. It is composed of black iron minerals and reddish-brown dolomite. It is now 2.5 billion years old. On the earth 2.5 billion years ago, the main components of the atmosphere were nitrogen and carbon dioxide, with almost no oxygen. At that time, there were many kinds of anaerobic microorganisms in the ocean. They breathed carbon dioxide in the water and released oxygen as metabolic waste. Oxygen combined with dissolved iron ions to produce this beautiful iron ore. Now it is the elemental iron we extract. The main ore.
Red hematite contains the remains of tubular microorganisms
Seeing this all-black rock formation, maybe you will be able to react soon, this is a combustible rock-coal. Most of the coal we use now is around 355 million years old, and a few are between 65 million and 150 million years old. The climate was warm and humid in the years when coal was formed, and a large number of ferns lived on the land. However, the tsunamis and floods also took off from time to time, causing large tracts of plants to die. The upper plant corpses slowly decayed, and the plants that were pressed down on the lower level could not be exposed to oxygen, nor were they decomposed by microorganisms. Slowly, their water evaporates, and finally only black organic matter is left, which forms the coal we see. According to geologists, a plant carcass about 6 meters high can form a 0.3 meter thick coal seam.
On the beach, we often see a white stone called diatomaceous earth, which is an ore formed from the corpses of a single-celled plant diatom. It is very young and fragile, with an age of only 2 to 25 million years old, and it can leave scars on its body with nails. Diatoms live in shallow water and survive by absorbing silicon in the water body. In places with frequent volcanic activity, the water body will contain a lot of silica. Diatoms like to live in such an environment. Therefore, the place where diatomaceous earth exists often indicates that volcanic activity has occurred in the past.
Passengers, this train is coming to the station, but the story recorded by the rock is far from over. They will be passed on for a long time. You are welcome to listen to it next time.