Nigeria has a rural economy that most Nigerians support becaus it is mostly based off of productivity of land. 31% of this land is cultivated. The soil fertility there varies but mainly poor. Poor because most of the soil there is mainly, always overused or eroded. Trees help prevent the soil from eroding but the Nigerians use the trees for materials they need. The tree are starting to barren, mostly around large cities. Petroleum and natural gases are the main earnings Nigeria gets from their exports. The reason to this is because they are concentrated in large amounts. Now, iron ore is generally low grade. Other low graded land resources they have are lignite (brown coal), limestone, subbituminous coal (ordinary cool but low graded and higher grading than lignite), tin, and columbite. Petroleum and natural gas industries have damaged the land majorly by having oil spills, burnoff of natural gas, and clearance of vegetation. This damaged the vegetation and waterways in the Niger Delta.