What is earth
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Explanation:

Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continents and islands. The remaining 71% is covered with water, mostly by oceans but also by lakes, rivers, and other fresh water, which together constitute the hydrosphere. 

Earth is a beautiful planet that revolves around a star called Sun, which is located in one of the arms of our Milky Way Galaxy. It is the only planet known to support life in the Solar System. Humans are the most intelligent civilization on this planet. It's blue when seen from space. Recently, Earth 29 spacecraft was able to land on this planet, after 28 unsuccessful landings of Earth series of spacecrafts. We were able to learn many things about humans, most important of these was the most spoken language of them, which they call English. According to experts, humans are not yet ready to know about our existence. It can take about 1 or 2 more centuries, until they are ready to know about us.

a- all cells come from pre-existing cells

what school and grade?