The oceans

As far as our present knowledge goes, Earth is unique in the solar system: It is the only planet with water in all three forms – solid, liquid and vapour – that coexist on its surface. Most of us have experienced landscapes along our vast sea shores, but in general humankind knows much less about conditions at the other side of the shoreline, in the oceans which cover 70 % of Earth’s surface! Before the 20th century little was known about the origin of oceans, their topography and depth or about life in them and we are only gradually coming to understand the oceans with all their geologic diversity – a fragile environment that holds a large part of Earth’s biologic heritage. In the last decade, 2700 scientists from more than 50 nations participated in the “Census of Marine Life, a Decade of Discovery”. Click on the Census of Marine Life Layer in Google Earth to learn more. The work realized by this Census, while substantial, has only scratched the surface of what remains to be learned about what lives and may live in the world’s oceans. The Age of Discovery is not over! This chapter discusses our knowledge of water movement in the oceans as currents, tides and waves and we briefly overview how sea level variations have created many coastal landforms that attract us for holidays, adventure or economic reasons.