In the next two chapters we will take a tour aboard an imaginary hover car to visit the world’s continental shelves and coral reefs. The continental shelf (as the name suggests) is the submerged part of the continents and the features we see underwater are comparable to those we see today along the coast. The continental shelf is where rivers disgorge their loads of sediment and where glaciers built moraines during the ice ageIce age, providing the material needed to make sand banks. Sand is in fact the second-most used commodity on Earth after fresh water. It is a key ingredient of concrete and is also used to replenish beaches that are eroding because of rising sea level. In this chapter we will observe the impacts of bottom trawl fishing on seabed habitats and consider the need for marine parks. To avoid burning fossilFossil fuels we should look at harnessing the ocean’s tide powerTide power as a renewable power source. Human impacts on land often reach the ocean. The Ok Tedi gold mine disaster in the Fly River, Papua New Guinea, is an example of this.