It cannot be said with conviction that the Earth is the only planet with any life on it because astronomers and space scientists are still trying to look for life on other planets. From what we know of other planets it is however established that life supporting conditions do not exist on any other planet in our universe. To be able to support life the planet must not have extreme variations in night and day temperatures, they must have an atmosphere which has the right mix of gases which can support life etc.
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As an example Venus which is closest to Earth has an atmosphere which is composed of carbon dioxide and clouds made of sulphuric acid –both of which cannot support the type of life that exists on Earth. Life is further nonexistent because the atmospheric pressure on Venus is very high and temperatures soar; up to 450° centigrade. There are small quantities of water on Mars but they are frozen because of the low temperature on this planet. From the above two examples and from what we know of the other planets we can see that, since none of the planets known to man so far have the necessary conditions required to support life no life has been found anywhere except on the Earth.
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