1. Uniformitarianism, or Actualism. 2. Multiple Working Hypotheses. 3. Principle of Parsimony 4. Inductive - Deductive Reasoning 5. Scientific Proof vs. Absolute Proof 6. Retrodiction – prediction in a backward direction. Uniformitarianism was developed by James Hutton in the 1790’s. Charles Lyell in the 1830’s popularized Hutton’s writings. James Hutton: first modern geologist (1790s) whose ideas were the basis for uniformitarianism 1 Charles Lyell, a founder of modern geology. He popularized Hutton’s ideas by coining the term uniformitarianism in the 1830s. Charles Lyell, 1797-1875 Lyell’s Grave in Westminster Abbey, London Uniformitarianism rejected supernatural explanations and held that present processes operated uniformly in the past. “The present is the key to the past.” 2 Many geologists use the German term actualism. Actualism - Physical and chemical laws are constant over geologic time. Mudcracks in a dried up pond Ancient mudcracks in sedimentary rocks. 3 Ripples formed by water flow on a modern beach. Ripples formed by water flow in an estuary. Ripples formed by wind on a sand dune. 4 Ripples in a sandstone, millions of years old, formed by water or wind. Ancient ripples preserved in sandstone 300 MY old in Colorado. The beds were originally horizontal but have been tilted by mountain building processes. Scientists seek as many explanations or hypotheses as possible for a given phenomenon. Each hypothesis is then tested. 5 If only one hypothesis is constructed, data may be collected to support only this hypothesis. Conflicting data may be ignored. The hypothesis will be bent to fit the new data. Absence of an alternative explanation is no assurance that the truth has been discovered. An example: Your car is missing from where you parked it. What happened to the car? It was towed. It rolled away down a hill. It was stolen. Your friend with a key borrowed it. 6 Extinction of the Dinosaurs Asteroid impact? Climate change? Disease? Volcanic eruptions? Competition with mammals? The best hypothesis is usually the simplest hypothesis (requires the fewest assumptions). Complex hypotheses are less likely to be true. Beware of clever hypotheses. e.g., who designed the Egyptian pyramids? Induction - developing conclusions from facts. Thought by some to be the essence of objectivity. Deduction - predicting results from a known principle. Induction-deduction work together. 7 Example: Sand bars form in flowing water (rivers, streams, or ocean currents). Induction These bars are cross bedded. Induction Thus, similar sized cross-bedded sandstones in a rock outcrop formed in flowing water. Deduction Sand bars in a river 8 Cross Beds FLOW FLOW Cross Beds that formed in flowing water FLOW Wind-blown cross beds are typically larger in scale than water-laid cross beds. 9 Scientific proof - a matter of probability. Absolute proof - a matter of certainty. e.g. a2+b2=c2 for a right triangle; or sodium and chlorine always form salt (NaCl); or the Second Law of Thermodynamics always applies. Few things are absolutely certain. Science deals with probabilities. Scientists cannot prove a hypothesis or theory to be true. Scientists can falsify hypotheses. Hypotheses that Hypothesis: cannot be falsified Dinosaurs went are the best extinct at the end of explanations the Cretaceous. available. How would you falsify this? Example: The blood type from the criminal at the crime scene does not match the defendant’s. What does that indicate? The blood type from the criminal at the crime scene does match the defendant’s. What does that indicate? 10 Good science requires accurate collection of data and an honest attempt to falsify available hypotheses. False hypotheses do little harm. False “facts” do great harm. Experimental Scientists use prediction to test their hypotheses. Historical Scientists use retrodiction to explain a past event. Example: plants grown in high CO2 concentrations have fewer stomata. Stomata density on fossil plants is used to estimate past CO2 levels in the atmosphere. 11.