Most likely there was more water on Earth a million years ago because the oceans formed about 3.8 billion years ago. Also, as the birth and death rates of organisms changed over a million years ago it must have affected the Earth's water "supply" having organisms use water to survive, and weather (rain) bringing in water. So, basically as time passed more organisms evolved and their needs evolved (adapt) such as the need of water- some needed less or more water depending on climate and adaptations- the growth of organisms and humans on earth must have slowly decreased the earth's water as we use so much of it.
