Q1.
Is the temperature or distance from the Sun, the only factor that makes the Earth habitable?
Answer
No. Distance from the Sun is the most important reason, because it is what allows water to stay liquid — but at least four other conditions must hold at the same time.
| Factor | What it does |
|---|---|
| Distance from the Sun | Places Earth in the habitable zone, so water is neither all evaporated nor all frozen |
| Nearly circular orbit | Keeps sunlight and heat almost steady through the year, preventing extreme summers and winters at most places |
| Size of the Earth | Gravity strong enough to hold an atmosphere, not so strong that our bones would be crushed |
| The atmosphere | Oxygen for respiration, an ozone layer that blocks ultraviolet rays, and a mild greenhouse effect that keeps the planet warm |
| Magnetic field | Deflects cosmic rays and the solar wind, protecting the atmosphere and the ozone layer |
Why it happens: These conditions are not a list of separate advantages — they depend on one another. The right size gives the atmosphere; the atmosphere gives the greenhouse effect and the ozone layer; the magnetic field is what keeps the atmosphere from being stripped away. Remove any one and the others start to fail too.