"earth"

Earth is the only home we have in the universe and the only planet we know of so far that has life on it, and because of this, we usually think of it as a perfect planet.

The earth was born more than 4 billion years ago, when it was very different from the earth of today, one of which is that the environment of cosmic space is more different.

The energy released by the sun's nuclear fusion reaction, in addition to making the sun shine and heat, there is an important role, that is, to resist its own gravity

In orbit for longer and longer periods of time, we need to solve not only inorganic resupply problems such as food, water, oxygen and propellant, but also the various problems faced by astronauts flying in orbit for long periods of time

If humans evolved from the forest archaeopteryx, how did the forest archaeopteryx emerge?

The earth's water resistance comes from the high temperature, pressure and density of its interior

At the time of the "family photo" of the solar system, the Voyager 1 probe has reached a distance of 6.4 billion kilometers from Earth, very distant, so in the view of the Voyager 1 probe, the solar system, the major celestial bodies are very small

The existence of reproductive isolation, so that these situations can not occur, even if there are some individuals of different species sometimes complete the mating, but they generally can not produce offspring, or produce offspring can not continue to reproduce

It has been billions of years since life appeared on earth, and although there are seven planets in our solar system in addition to earth, as well as a number of dwarf planets, moons and other relatively large bodies, so far we have not found alien life on any other planet in our solar system for the time being. Even mars, another earth-like planet in the habitable zone of our solar system, has not found a single sign of life. Could it be that life on earth is really unique and no other planet is allowed to have life?

For humans, the universe is too dimensional for us to see the details of its depths for the time being