Why is the planet earth the only planet with life?

Answer 1

It is not clear that Earth is the only planet with life. For all we know there might be, and most astronomers expect that there probably are, planets with life on them orbiting a significant fraction of the hundreds of billions of stars in each of the hundreds of trillions of galaxies in the universe. Present technology is barely able to detect that planets are there orbiting other stars, we cannot yet tell whether any exoplanets (as planets of other stars are called) have life on them.

As for the other planets in this solar system, Mercury and Venus are too hot to have liquid water on them, and Neptune and Uranus are too cold to have liquid water on them. Mars might have life remaining in its underground water, and there are speculations that life of a sort might be possible on Jupiter, Saturn, and the moon Titan, but (a) that's a long shot, and (b) we haven't looked yet.

A previous answer to this question said that Earth is the only planet with life because it is the only planet with nitrogen. That is utterly wrong. Mars, and Titan also have atmospheres consisting mostly of nitrogen, besides which nitrogen is a minor constituent of the atmospheres of Venus, Jupiter, Saturn, Uranus, and Neptune.

Answer 2

Earth is the only planet "so far" - we've only just begun to explore other planets.

Earth is the only planet with enough oxygen to sustain life. Also, the ozone layer protects us from the harmful rays that come from the sun.

Answer 3

In our solar system, Earth is in a favorable position with ideal temperatures for life not too close to the Sun (where water would be gaseous) and not to far away (where water would be solid and it would be a frozen world). Tidal effects are also believed favorable to life; as is the Earth's powerful magnetic field which helps prevent the atmosphere being swept away by the solar wind as may have happened on Mars, leaving it dry and arid. Some scientists indicate our solar system is also in a favorable position in the galaxy in terms of distance from the galactic core.

Current thinking is that there may be as many as 40 billion Earth-liike planets just in our galaxy alone and that likely many of these are likely to have life on them. It's also possible there might be life in subsurface oceans in moons of our gas giants Jupiter and Saturn, like Europa, Encedalus, and Titan - whose oceans are liquid because of warming effects from tidal forces.