Transcript Chapter 1
Welcome to Geology 100 at Miramar College Geology – the study of the Earth Physical Geology • materials that make up the Earth • processes that operate upon and beneath the surface of the Earth • this course is primarily a study of physical geology. Historical Geology • Understanding the origin of the Earth and its development through time • We’ll discuss some topics related to historical geology as well Catastrophism vs. Uniformitarianism How did the Grand Canyon form, over hundreds, thousands or millions of years? Catastrophism Catastrophism was the dominant explanation for the Earth’s landscape before the late 18th century. – People thought the Earth was only thousands of years old – This doctrine more easily fit in with religious beliefs of the time (think Flood). Uniformitarianism Uniformitarianism (aka Gradualism ), was the belief that the processes that were happening at a very slow rate, such as erosion and sedimentation, were responsible for shaping the Earth. It requires a belief in a very old Earth. Catastrophism AND Uniformitarianism • Catastrophism has made a “comeback”, with the acceptance of the impact theory for the last mass extinction • Now most scientists believe that the Earth is shaped by both both catastrophic events and gradual ones. The Nebular Theory • The solar system began as dust and gas (from an exploding supernova?) which then collapsed due to gravity. • The nebula contracted into a rotating disk. • Repeated collisions of rocky and metallic material coalesced into asteroid, then planet-sized bodies. • Age of the earth and solar system about 4.6 billion years (4600 million years). • Heating and subsequent cooling of Earth caused heavy metals to sink to the interior and lighter elements to rise to the surface. Earth’s internal structure The separation of heavy and light elements caused a layered Earth consisting of: – Crust: silica (SiO2)rich composition – Mantle: silica and iron composition – Core: iron and nickel composition The crust and mantle are further divided into “spheres” depending on density and physical state (e.g. solid or molten). Earth’s “spheres” by physical state • Lithosphere – rigid solid which make up the tectonic plates, includes both crust and the uppermost part of the mantle. • Asthenosphere – partially molten “weak” layer directly beneath the lithosphere • Mesosphere – lower mantle, mostly solid • Core – outer core (molten) – inner core (solid) Crust (part of the lithosphere) Continental and Ocean Crust • Continental crust – – – – thicker (average 35-40 km) older (up to 4 billion years old) less dense than ocean crust. varied composition (generally granitic). • Ocean crust – thinner (averages 5-7 km ) – younger (200 million years old or less) – more dense and iron-rich – composed of dark volcanic basalt. The Scientific Method Steps of the Scientific Method 1. Observe some aspect of the universe and collect facts about the observations. 2. Develop a tentative explanation, or hypothesis, about the observations. 3. Make a predication about some behavior, based on your hypothesis 4. Develop an experiment to test the prediction . Accept, modify or reject the hypothesis on the basis of extensive experimentation. 5. When consistency is obtained the hypothesis becomes a theory: In science, a theory is not “just some theory”! • A hypothesis becomes a theory after extensive testing and when competing hypotheses have been proven false • These provide a framework within which observations are explained and predictions are made for a particular part of the natural world • Examples include the theory of evolution and the plate tectonic theory. Scientific Method Flow Chart Attributes of the Scientific Method • Falsifiable: an experiment, observation or possible discovery must exist that could prove or disprove the theory. • Unprejudiced: one does not have to believe a given researcher; one can redo the experiment and determine whether the results are valid. • Repeatable: experiments and observations must yield the same results each time. Most are repeated many times to ensure consistency. Application: Do Glaciers Flow? • Observation: glacial debris found down valley • Hypothesis: glaciers used to be further down valley, and melted back. • Experiment: If we embed an object in the glacier, over time will it move uphill, downhill, or not at all? Do Glaciers Flow? • Experiment: put stakes into glacier and observe relative movement over time • Modified hypothesis (based on results of experiments): – glaciers do flow, but it’s down valley, not up valley – Center moves faster than sides – glacial melting responsible for glaciers apparent move up valley The Rhone Glacier over Time Investigation: Intelligent Design Intelligent Design (ID): the belief that certain features of the universe and of living things were created by an intelligent “designer”, not an undirected process such as evolution. The hypothesis avoids specifying the nature or identity of the “designer”, although its primary proponents believe the designer to be God. Is intelligent design a science? There has been some controversy about teaching ID as an alternative to evolution. Evolution is one of the key principles behind the Geologic Time Scale (p. 7 in text). Intelligent design should not be taught in a science classroom if it’s hypotheses cannot be tested by the scientific method. Should ID be taught as a science? • Observation: features of living organisms seem too complex to have been produced by a random process such as natural selection: • Hypothesis: Living things were designed by an intelligent entity • Experiment???? • Conclusion???