An Introduction to Physical Geology

1. An Introduction to Physical Geology Chapter 1

2. Geology • The science that pursues an understanding of planet Earth • Physical geology – examines Earth materials and seeks to understand the many processes that operate on our planet • Historical geology - seeks an understanding of the origin of Earth and its development through time

3. Geology, People, and the Environment • Many important relationships exist between people and the natural environment • Problems and issues addressed by geology include • Natural hazards, resources, world population growth, and environmental issues

4. Brief History of Geology • The nature of the Earth has been a focus of study for centuries. • Aristotle: • Influential Greek philosopher from 300s BC. • Made arbitrary pronouncements about natural world • Beliefs held throughout Middle Ages

5. Dueling Theories—17th & 18th Centuries • Catastrophism: Sudden world-wide upheavals. • Uniformitarianism: Processes occurring today also occurred in the past at about the same rate. • James Hutton said "The present is the key to the past." • Most widely accepted geologic theory today. • Birth of modern geology as a science.

6. What Does it Mean to be a Science? • Science assumes the natural world is consistent and predictable • Goal of science is to discover patterns in nature and use the knowledge to make predictions • Scientists collect data through observation and measurements

7. The Nature of Scientific Inquiry • How or why things happen are explained using: • Hypothesis – a tentative (or untested) explanation • Theory – a well-tested and widely accepted view that the scientific community agrees best explains certain observable facts

8. The Nature of Scientific Inquiry, cont’d • Scientific method involves • Gathering facts through observations • Formulation of hypotheses and theories • There is no fixed path that scientists follow that leads to scientific knowledge

9. Example of Transformation from Hypothesis to Theory • Brief history of plate tectonics • Early 20th century-continents and oceans believed to be fixed features on the surface of the earth • “Continental drift” hypothesis was proposed and ridiculed • Over 50 years of research before hypothesis transformed into the theory of plate tectonics

10. Geologic Time • Earth is approximately 4.6 billion years old • Oldest rock on earth: 4.4 byo • Relative ages based on fossil record Relative dating means that rocks are placed in their proper sequence or order without knowing their specific age • Absolute ages based on isotopic dating

11. Geologic Time Magnitude of geologic time • Involves vast times – millions or billions of years • An appreciation for the magnitude of geologic time is important because many processes are very gradual

12. A View of Earth • Earth is a planet that is small and self-contained • Earth’s four spheres • Hydrosphere • Atmosphere • Biosphere • Geosphere

13. Earth as a System • Earth is a dynamic planet with many interacting parts or spheres • Earth System Science • Aims to study Earth as a system composed of numerous interacting parts or subsystems • Employs an interdisciplinary approach to solve global environmental problems

14. Earth as a System, cont’d • What is a system? • Any size group of interacting parts that form a complex whole • Open vs. closed systems • Feedback mechanisms • Negative feedback – maintains the status quo • Positive feedback – enhances or drives changes

15. Earth as a System, cont’d • The Earth system is powered by the Sun that drives external processes in the • Atmosphere • Hydrosphere • At Earth’s surface • The Earth system is also powered by Earth’s interior

16. Earth’s Interior • Layers defined by composition (density) • Crust • Mantle • Core • Layers defined by physical properties (strength) • Lithosphere • Asthenosphere • Mesosphere • Inner and outer core

17. Chemical Divisions of the Earth • Crust • Uppermost surface of the Earth • Thinnest layer • Largest variety of rock types • Mantle • Below the crust • Composed of igneous and metamorphic rock • Core • Below the mantle • Composed dominantly of iron with some nickel and other elements

18. Physical Divisions of the Earth • Lithosphere • Crust and strong part of upper mantle • Makes up the tectonic "plates" of plate tectonics • Asthenosphere • Weak part of upper mantle • Partially molten in some areas • Lithosphere moves over this part of the mantle • Mesosphere • Lower mantle • Stronger than asthenosphere

19. Physical Divisions of the Earth, cont’d • Outer Core • Liquid • Composed of Fe with some Ni and other elements • Inner Core • Solid • Same composition as outer core

20. The Face of Earth—the Crust • Earth’s surface • Continents • Oceans • Continents • Mountain belts • Most prominent feature of continents • The stable interior • Also called a craton – composed of shields and stable platforms

21. The Face of Earth, cont’d Ocean basins consist of • Continental margins • Deep-ocean basins • Ocean ridge system

22. Ocean Basins • Continental margins • Includes the continental shelf, continental slope, and the continental rise • Deep-ocean basins • Abyssal plains • Oceanic trenches • Seamounts • Oceanic ridge system • Most prominent topographic feature on Earth • Composed of igneous rock that has been fractured and uplifted

23. Major Types of Rocks • Igneous rocks • Sedimentary rocks • Metamorphic rocks

24. Igneous Rocks • Cooling and solidification of magma (molten rock) • Examples include granite (intrusive) and basalt (extrusive)

25. Sedimentary Rocks • Accumulate in layers at Earth’s surface • Sediments are derived from weathering of preexisting rocks • Examples include sandstone and limestone

26. Metamorphic Rocks • Formed by “changing” preexisting igneous, sedimentary, or other metamorphic rocks • Driving forces are heat and pressure • Examples include gneiss and marble

27. The Rock Cycle • The loop that involves the processes by which one rock changes to another • Illustrates the various processes and paths as earth materials change both on the surface and inside the Earth

28. Demonstrate GEODe