well for a start 70 % of the earth's surface cover by ocean.let's put that into context.what that means is that we could put all of the land into the pacific ocean and still have room left over for nearly two more Australians.As we'll see later in this module,life is self evolved in the ocean.This happened about 3.9 billion year ago when there was no free oxygen in the atmosphere and the early cells obtained their carbon.which is an element essential to all life from carbon dioxide and their energy from inorganic material.cyanobacteria are relatively simple single celled organisms that obtain their energy from photosynthesis.They evolved in the ocean about three billion years ago,that's 3000 million year ago.and that led to the great oxidation event,2.3 to 2.4 billion year ago,when free oxygen started to accumulate in the atmosphere.Multicellular life forms evolved in an oxygenatted world.still in the ocean about 600 million year ago, which eventually led to the colonization of land about 450 million year ago,so there's been life in the oceans about 3.45 billion years longer than there's been life on land and there are many reasons why the oceans are important as