On the one hand, this enormous distance is something great because if the Earth were closer, the amount of light and energy that it would receive would be much higher. Therefore, the temperature would increase, putting the development of life in danger. On the other hand, if we were further, it would be the opposite: the lack of energy and low temperatures would make the living existence on our planet difficult.
Another interesting feature is that Earth’s orbit is almost circular (is indeed an ellipse), and that makes our radiation levels neither lower nor higher. An eccentric orbit would cause us to get very close to the Sun in a short time, but in that period, life would experience significant changes: it would be fire everywhere and a lot of UV radiation which would kill bacteria, causing damage to the living creatures here on the Earth surface. The rest of the time, we would be far from the Sun, which would bring a brief ice age every year, and by the freeze of everything and the lack of both energy and light, it would be significantly hard to survive.
The term “habitable zone” or “circumstellar habitable zone” was created to describe a place as the one the Earth has in space, which means, in a stable, almost circular orbit at the exact distance of its star. This term refers to the space region around a star, where the temperature of an object or planet is between 0 °C and 100 °C, and water in liquid state is possible under normal pressure conditions.
Venus and Mars are in the inner and outer bounds of the habitable zone. However, it is needed much more than the right temperature to the existence of life. Next, we are discussing four essential conditions for habitability on Earth.
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