Home Science Four billion years ago, there were three ‘Earths’ in the solar system,...

Four billion years ago, there were three ‘Earths’ in the solar system, why is there only one now?


In the solar system, and even in the entire universe, Earth is the only planet known to have life. Humanity has conducted a series of explorations of the solar system, and is still actively receiving signals from possible alien civilizations, but the result is still no trace of life. on planets other than Earth.
If we go back 4 billion years, there would be three “Earths” in the solar system, and life could have evolved on them. One of these “Earths” will of course be our present Earth, and the other two are Venus and Mars.

In the past, all three planets were rocky planets, the surface of which was composed of solid metals and silicates. Among them, our Earth is the largest planet, the mass and radius of Venus is only about 82% and 95% of the Earth, respectively, the mass and radius of Mars only account for about 11% and 53% when compared to our planet. Over the past few decades, humans have launched many unmanned probes to Venus and Mars, and it turns out that the environments on these two planets are very harsh. Venus is too hot, and Mars is too cold, and there is no oxygen on either planet, so life on Earth could not exist in such an environment, and astronomers could not find it. see any other traces of life there. So, how were Venus and Mars 4 billion years ago? Why are Venus and Mars now barren, and only our planet is habitable? Calculated based on the radiant power of the sun, Venus and Mars also operate in the same habitable zone as Earth, which means they can receive just the right amount of solar radiation to water. on their surface can still be in a liquid state. Astronomers speculate based on current signs on Venus and Mars and surmise that there may have been an ocean of liquid water on both Venus and Mars 4 billion years ago. For the first few hundred million years, Venus was a warm and humid planet. In the primordial oceans of Venus, life was fully qualified to evolve. They could be carbon-based life like life on Earth or could be other life forms. However, Venus’s habitable period did not last long. Because Venus is so close to the sun, and the temperature of the sun gradually increases over time, making Venus hotter and hotter, and a large amount of liquid water has also been evaporated. At the same time, the volcanic activity on Venus is also gradually becoming more active and continuously releasing carbon dioxide, causing a strong greenhouse effect. Without oceans, carbon dioxide would not be neutralized. They enter the atmosphere and cause a severe greenhouse effect, which will increase the temperature on Venus. Meanwhile, on Earth, the oceans, plants and minerals absorb large amounts of carbon dioxide, so the Earth will not become too hot due to the strong greenhouse effect during that period. Eventually, Venus’ greenhouse effect was completely out of control, liquid water completely evaporated, and life could have been destroyed. According to data returned by the Venus probe, the current concentration of carbon dioxide in Venus’s atmosphere is as high as 96.5%, and the surface atmospheric pressure is 91 times higher than the Earth’s surface. Under the influence of this extreme greenhouse effect, Venus has essentially reached thermal equilibrium, and the average surface temperature is as high as 464 degrees Celsius. Although it is essentially impossible to have life on the surface of Venus today, some astronomers speculate that there may be some strange life in the atmosphere of Venus. In the sky high enough above the surface of Venus, the atmospheric pressure will be moderate, and the temperature will not be high, possibly for the synthesis of organic matter and the evolution of life. On the other hand, ancient Mars was probably also a habitable planet. Currently, on Mars there is a large amount of water-washed terrain, and there are some iron ores that can only be generated in the aquatic environment, which is strong evidence for the existence of a large amount of water. liquid water on ancient Mars. So, how did Mars become such a uninhabitable planet as it is? At present-day Mars’ North Pole, there is a giant basin whose surface is equivalent to two-fifths of the surface of Mars. This huge Arctic basin was formed by a massive collision. Studies have shown that about 3.9 billion years ago, a dwarf planet (about the size of Pluto) with a diameter of about 2,000 km collided with the north pole of Mars. This massive collision completely changed the core of Mars, causing activities inside Mars to quickly stop, and the Martian magnetic field also gradually weakened and finally almost disappeared. lost. Without the protection of the magnetic field, the solar wind gradually strengthens and melts the atmosphere of Mars, liquid water continues to evaporate, causing Mars to quickly become a barren land. Currently, there is almost no atmosphere on Mars, but there is still some water ice in the polar regions. In addition, there may be a seasonal amount of liquid water in some areas of Mars, which has a high salt content and may be temporarily liquid in the low-temperature Martian environment. At the moment, the temperature on Mars is very low, the average temperature is only -63 degrees Celsius. If humans want to settle on Mars in the future, the first thing to do is to strengthen the star’s magnetic field. Mars and produces large amounts of greenhouse gases to “heat” Mars and melt the solid water that exists on Mars. Mars is much smaller than Earth, so it would have cooled from its molten state at its inception faster than Earth, so liquid water on Mars may have appeared earlier, which could This means that life on Mars may have formed and evolved earlier than our planet. Therefore, there are conspiracy theories that, when celestial bodies collided with Mars, the rocks that were thrown into space by the collisions could have carried the germ of life on Mars into space, and then some someday fall to Earth, becoming the source of life on Earth. And perhaps by coincidence, life on Earth also began to form around the same time that Mars’ North Pole collided. From the point of view of time, this is consistent. In addition, astronomers have discovered traces of suspected life in meteorites on Mars that have fallen to Earth. Life on Earth may have originated on Mars, but this has so far required more convincing evidence. In the past, the Curiosity rover has detected some carbon-containing organic substances in the rocks on Mars, which may be evidence that ancient Mars once had a few living things. Even now, it is still possible for life on Mars, they did not go extinct billions of years ago, but moved into the Martian underground and developed a unique survival mechanism to adapt to the harsh environment. harsh on this planet. Compared to Venus and Mars, our planet is very lucky. For billions of years, Earth has always been a habitable planet, so hundreds of millions of species have appeared here. Our Earth is like a “chosen planet”, a moderate distance from the sun, with a magnetic field that can resist solar radiation so that all kinds of life can continue to multiply and develop. Although it cannot be ruled out that some planets in the solar system (such as Europa) also harbor life, the environments of those planets are very different from those of Earth, and most life on Earth is not ruled out. Soil cannot exist there. In the near future, Earth will still be the only planet inhabited by humans in the universe.