Four Element metals are the main compounds of value in manganese nodules and Cobalt crust: manganese, copper, nickel, and Cobalt. In addition, Cobalt crust contains Platinum Group metals and rare earth metals, and precious metals such as gold and silver or percentage in sulphides. Although the gross revenue is potentially high technology, legal and environmental problems are showing down the rise of a flourishing commercial industry. Metal compounds, gravel, sand and gas hydrates are also mined in the ocean. Mining of Manganese nodules containing nickel, copper, and Cobalt began in the 1960s and soon after it was discovered that Papua New Guinea was one of the few places where nachos were in shallow waters rather than deep waters. Although manganese nodules could be found in Shallow Waters in significant quantities, the expense of bringing two are up to the service provided to be expensive. Sand and gravel are often minded for in the United States and are used to protect beaches and reduce the effort of erosion.