The oceans and seas cover about 70 per cent of the Earth's surface. This statistic alone tells us that the aquatic environment is much bigger in terms of area than the land environment but when we also consider the sheer depth of the ocean - 11km 7 miles deep in places - then we see that the potential space available for marine life to exist is staggeringly huge. In fact about 90 per cent of the Earth's living space is in the ocean or under the seabed.