Where does the oxygen we breath comes from?

Gaseous oxygen was created on the Earth about 3.5 billion years ago. At that time the UV light of the sun decomposed the water vapour molecules present in the atmosphere, and released oxygen and hydrogen. But a major part of the oxygen immediately reacted with other substances, so that it was no longer available in the atmosphere as gas. Oxygen was also produced by the seas, where the 'blue algae' carried out photosynthesis. These bacteria converted sunlight and carbon dioxide into energy. In the process, gaseous oxygen was released as a 'waste product', which accumulated in the atmosphere. About one billion years ago, about one - twentieth (4%) of the atmosphere consisted of oxygen.

What would happen if there was no water on the Earth?

Without water, there would be no animals or plant, which carry out photosynthesis and release oxygen, and consequently the oxygen content in the atmosphere would go down. Moreover, the absence of oceans would have serious consequences as they help to keep the Earth's climate moderate by storing heat inside them. Without large water bodies, the temperatures of the sunlit areas and those away from the sunlight would change drastically. The temperature difference between day and night and between summer and winter would by very large. As a result, hurricanes would be a constant occurrence on the Earth.

Is there life on any planet other than the Earth?

There is no life on the other planets in our solar system because their environments are not favourable for life. They are either too hot, too cold, or too stormy. The only place that can be assumed capable of sustaining life is Europa, the moon of Jupiter. Scientists say that an ocean of liquid water could be present on this celestial body under a 10 km thick layer of ice. They also say the civilizations like our could be present - if at all - only outside of our solar system.