Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice. There are two types of weathering: mechanical and chemical. Mechanical weathering is the disintegration of rock into smaller and smaller fragments. Frost action is an effective form of mechanical weathering. When water trickles down into fractures and pores of rock, then freezes, its volume increases by almost 10 percent.
(July 2002) Despite the fact that sub-Saharan Africa contains only about 11 percent of the Earth's population, the region is the world's epicenter of HIV/AIDS. The numbers are daunting. Adult HIV prevalence is 1.2 percent worldwide (0.6 percent in North America), but it is 9.0 percent in sub-Saharan Africa.
In accordance to 2013 estimates, more than 44 million people are infected by HIV AIDS from which the majority of individuals belongs to Africa.There are many nations having the highest number of AIDS infected people following is a list of top ten countries with highest AIDS rates in the world.n accordance to 2013 estimates, more than 44 million people are infected by HIV AIDS from which the majority of individuals belongs to Africa.There are many nations having the highest number of AIDS infected people following is a list of top ten countries with highest AIDS rates in the world.