Well, on the one hand, there is overwhelming evidence for evolution that has taken place over the last several hundred million years and an earth that is billions of years old. (Based on the evidence, scientists think the earth is about 4.6 billion years old, and that life has been evolving for 3.8 billion years.) For example, scientists have carbon-14 dated some remains of physically modern humans to over 30,000 years old. The oldest cave paintings have been dated to 32,000 years ago. The fossil remains of dinosaurs and mammals show the transitional forms one would expect from evolution, enabling archeologists to construct a tree of evolutionary relationships (with varying levels of confidence.) Et cetera. Based on all this evidence, many LDS, including many here, believe in evolution and an earth that is billions of years old. On the other hand, there is D&C 77:6: This, we should note, is not supposed to be Joseph Smith's personal theory. According to Joseph Smith, this is a direct revelation. So, according to this, the earth has seven thousand years of "temporal existence" (presumably including The Millennium.) Thus, if the earth existed prior to 6,000 years ago, it had to be in an "eternal state." This would mean that nothing could change or die. Yet evolution is change, and natural selection requires death. Anyway, that's my two cents. Does that help clarify anything?