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Among the eight planets in the Solar System, the Earth we live in is really special. Not only is it the only planet in the Solar System known to harbour life, it also evolves some highly complex and even intelligent life. What are the factors that make it such a unique planet?
First of all, during the 5 billions years since the formation of the Solar System, the Earth has been located at the Habitable Zone of it. Planets within that zone are at reasonable distance from the Sun. The surface temperature of those planets allows liquid water to exist, providing a very favourable condition for the beginning and evolution of life. Venus and Mars, our neighouring planets, are just located at the inner and outer rims of the Habitable Zone respectively. As a result, Venus is hot like hell for reason of the runaway greenhouse effect whereas the surface of Mars is so cold that water can only exit in the form of ice.
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| Mars is located outside the habitable zone. Liquid water cannot exist on its surface.(NASA) |
Secondly, the existence of the super massive Jupiter did affect the formation and development of other planets . When the Solar System was newly formed, the huge gravity of Jupiter pulled planetesimals away from the Sun, indirectly putting the Earth under a collision barrage of objects of various sizes during the first hundred millions of years after the formation of the Earth.
hese violent impacts increase the amount of basic elements of life, water and organic compounds, on Earth. When most objects near the Sun were removed by the pull of Jupiter, the giant planet in turn became the protective barrier of the inner solar system, shielding inner planets like Earth by minimizing impacts of huge external objects. Without the protection of Jupiter, it is estimated that the Earth will be subject to a catastrophic collision every hundred thousand of years. Even if life can survive these disasters, it is difficult for them to develop into advanced life form. On the contrary, occasional destructive impacts might have wiped off 90% of life on Earth. Yet drastic changes in the environment may simultaneously trigger evolutionary breakthrough. New species flourish in the aftermath evolving into various kinds of complex life. Besides, by reason of its long distance from Jupiter, the Earth can maintain a rather circular orbit. Also the gravitation of the Moon can stabilize the tilt of the rotational axis of the Earth , thus restricting climatic fluctuation within a narrow range. The tidal force of the Moon has been slowing down the rotation of the Earth, making the change of day and night rhythm infrequent. All these are conducive to evolution of life.
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| The huge Jupiter is like a cosmological vacuum cleaner, shielding inner planets from many impacts of external objects.(NASA) |
Moreover, heat energy generated during decay of heavy elements like uranium at the centre of the Earth triggers tectonic movement. Tectonic movement in interaction with the ocean, atmosphere and living things form the Carbon Cycle, adjusting the carbon dioxide content in the atmosphere and stabilizing the surface temperature on Earth. Besides, vegetation on Earth has been carrying out photosynthesis non-stop for over 3 billions years, filling the Earth atmosphere with oxygen. This not only sustains most living things but also forms the ozone layer, shielding life on Earth from injury of UV rays.
The Earth is blessed in a way as to allow life to multiply and evolve, making Earth a vibrant dynamic planet in the Solar System.
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