When an animal or plant of many cells breaks up into two or more parts, and when these parts survive to produce a new organism, reproduction occurs by ?

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?