Geologic Time. Relative Dating. Principle of Original Horizontality. Relative Time. Absolute Time. Geologic Column

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1 Geologic Time Relative Time 5 Principles of Relative Dating Absolute Time Radiometric Dating Geologic Column Relative Dating principle of horizontality principle of superposition principle of cross-cutting principle of inclusion principle of faunal succession Principle of Original Horizontality Rocks are deposited in horizontal layers

2 Principle of Superposition Rocks on top are the youngest; oldest on the bottom Principle of Crosscutting Rock that is cross cut is older than the formation (faults, cracks, rocks) that did the cutting. Youngest In between Oldest.

3 Principle of Inclusion Rock that is included in (surrounded by) other rock must be older than the surrounding rock unconformity Principle of Faunal Succession Fossil assemblages (groups) found in sedimentary rocks are diagnostic of rock age. Extinct assemblages never appear in younger rock. Faunal Succession Organizing the Fossil Record William Strata Smith (1790) Smith, an engineer and surveyor, noticed that certain fossils were peculiar to certain strata. In time, he got so good at it, you could give him a box of fossils and he could immediately tell you what stratum they came from. For 200 years, geologists have been extending this skill and data.

4 Application Now You Try It

5 Uniformitarianism Catastrophism earth is young, geology from rare cataclysmic events Uniformitarianism James Hutton natural laws do not change with time cause and effect relationship between natural laws of geological processes occurring on earth understanding the natural laws and processes place limits on rates of processes Absolute Dating: The Age of the Earth Ocean salinity (100 million years) Rate of sediment deposition ( Million years) Heat loss ( million years) Radiometric dating (4.6 billion years) Not absolute provides a range a times Radiometric dating Measure amount of daughter isotope to parent isotope and determine the time required for that decay. Problems: Assume no daughter isotope 1200 originally present Isotopes should be relatively 800 common with long half-lives. counts time 235 U 232 Th 238 U 207 Pb (713 million years) 208 Pb (13.9 billion years) 206 Pb (4.5 billion years)

6 The Geologic Column Cenozoic more complex plants and animals mammals Second Great Dying 66 million years ago Mesozoic First Great Dying birds, mammals, flowering plants dinosaurs 245 million years ago Paleozoic fish and reptiles marine invertebrates Cambrian Explosion 570 million years ago Pre-Cambrian worms and soft bodied creatures primitive life First life ~3.2 billion years ago Age of the earth ~4.6 billion years President Hugh B. Brown, 1958 But while very little was written originally on the details of the creation of the world and man s advent upon it, it should be observed that God is the author of two accounts of creation. One is written in the Bible and amplified by modern revelation and the other was written in the strata of the earth. Each has at times been wrongly interpreted and misunderstood and they sometimes seemed to be contradictory or at variance. If you will remember that these two records have the same divine Author, you will know they cannot be fundamentally opposed, though man s interpretation of either or both may be seriously at fault.

7 Brigham Young..In these respects we differ from the Christian world, for our religion will not clash with or contradict the facts of science in any particular. You may take geology, for instance, and it is a true science, not that I would say for a moment that all the conclusions and deductions of its professors are true, but its leading principles are; they are facts they are eternal; and to assert that the Lord made this earth out of nothing is preposterous and impossible..whether he made it in six days or in as many millions of years, is and will remain a matter of speculation in the minds of men unless He give revelation on the subject. Journal of Discourses