Which of the following fossils is not found within the rock layers of the grand canyon?
a. trilobites
b. dinosaurs
c. stromatolites
d. armored fishes

American scientist, linus pauling, was one of many scientists racing to discover the molecular structure of dna. pauling initially thought that the molecule was a triple helix. later, james watson and francis crick unveiled their double helix model, which turned out to be an accurate description of the molecule's shape. why did watson and crick succeed when pauling failed?