PHSC 4013, Earth Science

1. PHSC 4013, Earth Science Mr. Brian M. Cudnik, Instructor 9 September 2008

2. Earth Geology vs. Planetary Geology • We will study the planets in more detail later, but it is useful to mention the parallels between Earth geology and planetary geology • By studying the processes that shape Earth’s surface both from without and from within, we gain the following: • We learn about the nature of these processes themselves and their origins • By so doing, we can look for similar results on other planets and infer past geologic history for that world • The following summarizes the geologic processes found on Earth (Note that these are external processes, we touched upon internal processes last time).

3. The Rock Cycle gives rise to three main types of rocks, based on their origins or means of formation • Igneous rocks originate from cooling and crystallization of magma from inside the Earth: Extrusive or volcanic igneous rocks form when magma is forced to the surface; Intrusive or plutonic igneous rocks are formed when magma cools inside the earth. • Sedimentary rocks result from the compaction and cementation of sediments formed on the surface by weathering, erosion, and deposition processes. • Metamorphic rocks are formed when pre-existing rock is altered or metamorphized by extreme heat, pressure, and chemically active fluids. • Rocks are classified by their texture and mineral composition; the rate of cooling of igneous rocks determines the size of the crystals that make up the rock (fast cooling means tiny crystals, slow cooling means larger crystals). • Some of the most important accumulations of metallic mineral resources are produced by igneous and metamorphic processes.

4. Internal processes also occur to shape the face of the earth: volcanism and mountain building get their energy from Earth’s interior heat • Differential weathering can occur depending on key variables that can affect its rate: climate, heat, and moisture patterns; chemical composition of the rock; and the degree of jointing and fracturing that occurs in the rock. • Mass wasting may be rapid or it may be gradual, and it may involve wet or dry materials. • The following are factors that influence changes in gravitational stresses on the materials: • water saturation of slopes, • oversteepening by erosion or human activities, • earthquakes, or • vegetation removal.

5. The Forces that Shape the Earth both Inside and Out • So far we have considered the materials that make up the Earth and briefly looked at its internal structure • We will look at the forces, both from the outside and from the inside, that shape the Earth as we know it. • The primary driver of the external sculptors of Earth’s surface is the Sun, driving the Atmosphere and the Ocean resulting in the following mechanisms • Weathering- the mechanical breakdown of rock by wind and water • Mass Wasting-the transfer of weathered rock, soil, and sediment downslope under the influence of gravity • Erosion-incorporation and transport of surface materials by wind, water, etc. (can you think of others, such as tornadoes and trees?...)

6. The Forces that Shape the Earth both Inside and Out • Agents of external weathering, erosion, and mass wasting include the following (don’t worry about memorizing the various types of stream and river drainage patterns…) • Streams and rivers, lakes and oceans, and groundwater • Glaciers and how these change the landscape • Rain, snow, hail, sleet, accumulation, melt • The forces that shape the earth from inside have a common driver: the internal heat of our planet • Review of the static and dynamic aspects of the interior of Earth… • How do we know what the inside of the Earth is made of? • Review of how this came to be over geologic time… • The vents of heat at the surface include volcanoes and plate boundaries

7. Plate Tectonics • The process of Plate Tectonics plays a major role in the shaping of Earth’s surface over long time spans • Plate tectonics describes the Earth’s crust as being broken into some 27 plates, great and small • The plates consist of lithospheric crust afloat on a “sea” of asthenosphere • Heating from below drives currents in the asthenosphere which in turn carries the plates along

10. Evidence for Plate Tectonics • Shapes of the Continents • Fossil Record and extant species distribution • Mineral and Rock distribution • Remote sensing shows: • Continents moving at the rate of 1cm per century • Mid-sea floor ridges producing new oceanic crust (sea floor spreading) • Magnetic field imprint evidence in sea floor…

11. Types of Plate Interactions • Divergent plate boundaries • Convergent boundaries (mountain-building, some types of volcanoes) • Transform boundaries (earthquakes)

13. In Summary… • External Energy Source—the Sun • Weathering, Mass Wasting, Erosion • Agents include Wind, Water, Landslides / Avalanches, Tornadoes, ice, rain, hail, etc. • The Sun also drives: the Water Cycle, Atmospheric currents and Weather, Ocean currents and climate, the Freeze and Thaw of ice caps, snow, glaciers, etc

14. In Summary • Internal Energy Source: the Earth (heat from within) • Plate Tectonics: Earthquakes, volcanoes, rock deformation and mountain building • Heat rising from the interiors of the Earth left over from the initial formation

15. The History of the Earth • Two types of dates used by geologists to interpret the history of the earth include: • Relative dates—puts the events in their proper sequence of formation • Numerical dates—which pinpoint the time in years when an event took place • Relative dates established by the law of superposition

16. The History of the Earth • Two types of dates used by geologists to interpret the history of the earth include: • Relative dates—puts the events in their proper sequence of formation • Numerical dates—which pinpoint the time in years when an event took place • Relative dates established by the law of superposition, principles of original horizontality, cross-cutting relationships, inclusions, and non-conformities.

17. The History of the Earth • Correlation-matching up of two or more geologic phenomena in different areas—most common example is the fossil record. • Radioactivity is the spontaneous break-up (decay) of unstable atomic nuclei and come in three common types: • Emission of alpha particles (helium nuclei) from the nucleus • Emission of beta particles (electrons) from the nucleus) • Capture of electrons by the nucleus

18. The History of the Earth • Radioactive decay • An unstable isotope or Parent will decay and form stable daughter products • Half-life is the length of time for half of a given sample to decay to daughter products • If the half-life of an isotope is known and the parent/daughter ratio can be measured, the age of a sample can be calculated • However, not all rocks can be dated radiometrically • An example is a sedimentary rock bed with particles of many ages weathered from different rocks formed at various times • Dates can be assigned by relating these rocks to datable igneous masses like volcanic ash beds.

19. Introduction to Critical Thinking Skills • In addition to the regular course material, I will be providing supplementary material detailing critical thinking processes • The introductory sheet will be provided separately in a word document • Each week, a Cognitive Skill and Affective Attribute will be highlighted briefly in class and in the class notes • Due to time and scope limitations, we will not do the exercises associated with these. We do them as part of another course, Introduction to Atmospheric Science • The material comes courtesy of the American Meteorological Society

20. Cognitive Skill of the Week: Interpretation Interpretation is "to comprehend and express the meaning or significance of a wide variety of experiences, situations, data, events, judgments, conventions, beliefs, rules, procedures, or criteria." (American Philosophical Association) A learner who looks at a weather map and is able to describe weather patterns, such as the circulation around high and low pressure centers, is demonstrating interpretation. Affective Attribute of the Week: Inquisitiveness Inquisitiveness is the inclination to be curious, to ask questions, and to thirst for knowledge. A critical thinker spends considerable time wondering about things and typically seeks more explanation and understanding. An inquisitive person is generally probing the unknown and habitually finds that seeking answers to questions invariably leads to more questions. A learner who has interpreted wind patterns on weather maps related to centers of high and low pressure begins to wonder why such circulation happens. That person is demonstrating inquisitiveness.