Why do some people say that Venus is the past of the earth and Mars is the future of the earth?

The saying "Venus is the past of the earth and Mars is the future of the earth" has a long history. Actually, I don't understand where it came from. I think Venus is more like the future of the earth, and Mars is more like the past of the earth. Then how should I say this? I'll just give my opinion.

Actually, Venus, Earth and Mars are all inside the solar system, and 99.86% of the mass of the solar system is the mass of the sun, so talking about things inside the solar system is definitely inseparable from the sun.

As a star, the sun is actually very lucky for the creatures on earth. What we need to know is that if a star is very big, it will soon be finished, such as Betelgeuse. Scientists don't think it can live for 2 million years, and it is not as long as life. To put it bluntly, the history of primates is several times longer than this. Therefore, this time is simply not enough to evolve higher life.

but if the star is too small, there will actually be a problem, that is, the brightness is not enough and the external radiation intensity is not enough. For example, if proxima centauri C is moved to the position of the sun, although its life span can reach more than 1 billion years, there is a high probability that the earth will become a snowball, not to mention the existence of life.

So, in fact, the size of the sun is just right. It is about 1 billion years in the prime of the main sequence star. In these 1 billion years, it is actually relatively stable and radiates heat continuously. However, what we need to know is that the sun burns by nuclear fusion reaction, which is similar to the hydrogen bomb. Then why didn't it explode at once? This is because the gravity of the sun itself and the external pressure generated by the nuclear fusion of the core form a dynamic balance, which makes the core of the sun realize the controlled nuclear fusion reaction.

But maintaining the controlled nuclear fusion needs gravity, which is related to its own mass. The sun burns 4 million tons of hydrogen every second, so its mass has been decreasing, its gravity has been weakening, and its binding ability to nuclear fusion has been weakening. Therefore, during the period of the main sequence star of the sun, the radiation intensity of the sun is gradually enhanced, and it will be greatly improved every billion years.