You are completely unaware about the science of oceanology! Just one reason for why the earth have to be 3/4 under sea (and there are many, many other reasons) is that the ocean of water serves as natural thermostat. Without this abundance of water regulating the temperature, it would be too hot in the day and too cold in the night for life to thrive. This 3/4 of earth covering with water has proved to be just right and to produce the climate that we all now can enjoy with.