The Amazon Rainforest is the world's largest tropical forest. Sprawling over nine countries, it is about half the size of the United States of America...But for several weeks now, the forest - also described as the lungs of the earth - has been on fire. More than 9,500 new forest fires have been spotted by Brazil's National Institute for Space Research in just the last two weeks...prompting international alarm and calling for urgent action. According to forest experts, Amazon almost never burns on its own and the increase in fires this year has been quite dramatic. The region is usually too wet to ignite, so the vast majority of fires are largely believed to be caused by humans.