BYU Geology Professor and Associate Dean of the College of Physical and Mathematical Sciences, Bart Kowallis, recently gave a presentation where he addressed the idea that the fossils in the earth can be accounted for by the theory that the earth was made from chunks of other planets. Here is the relevant discussion (he elaborates and provides evidence for his position in the link):
Some others have even used these data to explain fossils in the earth’s rock. These ideas do not hold up under scrutiny and a careful analysis of the available evidence. All of the evidence gathered from studying the earth indicates that its surface was molten and very hot early in its history. These conditions would have destroyed any fossils and the heat and the molten nature of the surface would have also reset any radioactive clocks to zero.