AST251H1 Study Guide - Midterm Guide: Igneous Rock, Silicon Dioxide, Silicate Minerals
23 Jul 2016
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We can figure that out by studying fossils. Three lines of fossil evidence to indicate life arose quite early in the earth"s history: stromatolites: rocks that are characterized by a distinctive layered structure. Living stromatolites contain layers of sediment intermixed with different types of microbes. These microbes adapt and migrate to create a layered structure of the rock. Stromatolites are the fossil remnants of early life. Carbon 13 accounts for about 1 out of 89 carbon atoms. Living organisms show a slightly lower fraction of carbon 13 than that found in inorganic material. In greenland, lower carbon 13 ratio has been found in rocks that are more than 3. 85 billion years old. Because rocks containing the isotopic evidence cannot be dated. Two species with similar dna must have diverged relatively recently while two species with very different dna probably diverged a long time ago. Dna studies tell us that life can be divided into three domain: bacteria, archea, eukarya.
