How much of the world's diversity is threatened as tropical forests are converted to agricultural use?
20 percent
30 percent
40 percent
50 percent

Paleontologists have found plant fossils deep within the layers of the north polar region. these leaf fossils have been labeled as to the rock layers they were found in, with the lower numbers being layers close to the earth's surface and higher numbers representing deeper layers. according to the numbers of these four leaf fossils, what might you infer?