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For multiple choice questions about the skeleton of life, the answer can be C.
We are all children of the stars!
- Karl Sagan
About 13.8 billion years ago, the universe was in a state of extreme energy and density and extremely high temperature. After the Big Bang, after a long evolutionary process, it formed what we see today.
The Big Bang produced only three or four chemical elements (hydrogen, helium, and lithium, and possibly beryllium), and the more "heavy" chemical elements that followed came from "stellar element processing plants." Generations I and II combine lighter elements into heavier elements through nuclear fusion and supernova explosions. From this point of view, every molecule and atom of life in our solar system, on Earth, and even on Earth comes from their contribution, so "we are all children of the stars."
We are all children of the stars (Image: wiki)
In the beginning, the earth was actually very short of carbon
According to the current "condensation model" theory, the solar system formed in a nebula about 5 billion years ago. Because the Earth is closer to the Sun and belongs to an "inner planet", the lighter material on the Earth is "blown away" by the solar wind. In the end, the Earth appeared as a rocky "terrestrial planet" - dominated by the four elements of iron, oxygen, silicon and magnesium, while hydrogen and helium, the two most common light elements in the universe, were few. Fortunately, oxygen helps us lock in a lot of hydrogen in the ocean, so that we have a blue ocean. Otherwise, life may not have been born at all.
Artistic imagination, the planetary disk at the beginning of the formation of the solar system, where the Earth was born (Image source: wiki)
Although carbon has a high boiling point, it is easy to form methane, carbon monoxide and carbon dioxide that are gaseous at room temperature and pressure. The study found that after the temperature exceeded 500 K (about 230 ° C), the planet had difficulty binding carbon, and the carbon-containing gas began to disperse significantly into space. (This is the black "cliff" in the image below!) At the beginning of the Formation of the Earth, the inner solar system was a hot "soup", and 500K was an easily reachable temperature. In this case, Carbon on Earth clearly has its own ideas — it can be scattered and "sublimated" into space.
The thick gray line in the upper right corner is the sublimation sequence of carbon elements, which drops sharply by more than an order of magnitude when the temperature of the primordial nebula reaches about 500 K. This manifests itself in the fact that more carbon is lost, resulting in a planet that is "carbon-poor."
(Image: science advances)
This is also confirmed by the carbon content of the metal nuclei in iron meteorites.
Within the Solar System, iron meteorites formed within about a million years of the birth of the Solar System, so they can be considered samples of the original geochemical composition. Hirschmann, a professor of earth and environmental sciences at the University of Minnesota, published an article in the Proceedings of the National Academy of Sciences that pointed out that the carbon content at the beginning of the Formation of the Earth may have been only 140 ppm (ppm is part per million, one part million).
This is really minimal, you know, the carbon content in the earth's crust is about 300 ppm. (Other claims range from 200-1700 ppm, but are rare.) ）
It turns out that our planet suffered from "carbon poverty" syndrome at the beginning of its formation. According to this, Hirschmann said: "This subverts the previous idea that planets lose a lot of carbon during the accumulation process." ”
Hirschmann, professor of earth and environmental sciences at the University of Minnesota (Credit: University of Minnesota)
What a soot line is
This interesting phenomenon prompted scientists to delve into the early days of the formation of the solar system, and they proposed a concept called "soot line", in which carbon is almost not retained inside the "soot line" (near the sun), while outside the "soot line", carbon can retain a considerable amount.
After calculations, scientists found that before the formation of the sun, the solar system was mainly concentrated, and the "smoke and dust line" was quite far away, and the earth could not retain much carbon at all. When the sun "lights up", the solar system is mainly dominated by radiation, and the "soot line" is also moved inward into the Earth's orbit, and the Earth can begin to accumulate carbon.
Schematic diagram of the "soot line": within the red line (soot line), there are very few carbon-rich substances. In the disc-like phase (lower part), dominated by accretion, it is far from the primordial sun. A million years later, the transition to a radiation-dominated epoch (the first half) will allow the soot line to migrate within Earth's current orbit. (Image: science advances)
Carbon is mostly in the form of carbonates in the earth's crust and mantle, and the core is the base camp of carbon elements, where there is a lot of iron carbide (Fe3C7). In response to this phenomenon, Professor Li Jie of the University of Michigan has made a final decision - through the study of the chemical composition of the earth's core through seismic waves, it can be learned that carbon accounts for about 0.5% of the entire mass of the earth (the aforementioned 300ppm is the abundance of the earth's crust), which is far more than the beginning of the earth's birth.
Where did C come from?
The question is, where does so much carbon come from?
Professor Jie Li from the Department of Earth and Environmental Sciences at the University of Michigan (Image: University of Michigan)
Professor Li Jie's team deduced that most of The carbon on Earth is likely to have been directly inherited from the interstellar medium. During the first million years of the formation of the solar system, a series of asteroids would exist, constantly transporting water and carbon farther beyond the "soot line" to Earth.
It turned out that in that chaotic era, the arrival of these "uninvited guests" of asteroids not only brought repeated impacts and disasters to the earth, but also brought valuable water and carbon elements in the solar system. (Until then, there has been more definitive evidence that water on Earth comes primarily from asteroids.) ）
The first geological epoch when the Earth first formed, the Pluto, was hit by meteorites everywhere. Yet it was these "uninvited guests" who brought us carbon and water. (Image source: wiki)
Water is the source of life, carbon is the skeleton of life, and all kinds of organic matter are built on the magical skeleton of the "carbon chain". Therefore, our planet is full of vitality today, and the critical period lies in this million years.
Thanking the interstellar medium on behalf of the biosphere (Image: wiki)
The process of carbon enrichment on planets is subtle. On the one hand, carbon is particularly prone to forming gaseous substances that escape into space. Carbon dioxide, on the other hand, is one of the most famous greenhouse gases, and it helps the planet lock in heat. If there is too much carbon on the earth, it is possible to be like Venus, the temperature is 460-480 ° C for a long time; and if there is too little carbon, it will be similar to Mars, too desolate.
In this sense, is the position of the earth really perfect, is this the Creator's arrangement, or is it anthropic principle? (In short, the anthropotential principle is intended to show that it is the existence of human beings that can explain the characteristics of our universe.)
Based on this research, scientists have pushed their horizons into distant deep space to continue observing super-Earths in exoplanets. With more data, existing theories will be more challenged and more convincing.
Venus and Mars, which happen to be located in the inner and outer reaches of Earth's orbit, are exactly the two extremes (Credit: University of Pennsylvania)
The study of this topic also reflects the necessity of interdisciplinary science. A stark example is the authors of the paper "Earth's Carbon Deficit caused by early loss through irreversible sublimation" from so many institutions and covering so many specialties.
List of authors of the paper "Earth's carbon deficit caused by early loss through irreversible sublimation," which Professor Li Jie is a contributor to.
Professor Ciesla, a geophysics major at the University of Chicago, said: "While researchers will differ in their approach and specific questions in different fields, building a coherent story requires identifying topics of common interest and finding ways to bridge the knowledge gap between them. While challenging, such efforts are both encouraging and inspiring. This is very beneficial. ”
Professor Ciesla of Geophysics at the University of Chicago
(Image source: University of Chicago)
bibliography:
[1] Science Advance：Earth’s carbon deficit caused by early loss through irreversible sublimation
Li, J., Bergin, E. A., Blake, G. A., Ciesla, F. J., & Hirschmann, M. M. (2021). Earth’s carbon deficit caused by early loss through irreversible sublimation. Science Advances, 7(14), eabd3632.
Author Affilications: Science Fiction Professional Committee of Jiangsu Science Writers Association
Further reading:
Out of line fred Hoyle | Liu Boyang
HOYLE: Wrong, not in the starry sky, but in our own | Yuan Lanfeng
Background: Lu Chao, the author of this article, is the deputy director of the Science Fiction Professional Committee of the Jiangsu Science Writers Association, and a member of the Jiangsu Science Writers Association. Graduated from the Department of Physics of Nanjing University, his representative work "Grimace Chemistry Class - Element Family" was listed as the "IYPT 2019 Excellent Popular Science Book" bibliography of the Chinese Chemical Society, and won the first prize of the 10th Jiangsu Provincial Excellent Popular Science Works. This article was published on May 7, 2021 on the WeChat public account Science Compound (Where did C come from?) ), the Voice of the Wind and Cloud is authorized to reprint.
Editor-in-Charge: Xinyue Chen