The science of Geology

3. The science of Geology • Geology is the science that pursues an understanding of planet Earth • Physical geology - examines the materials composing Earth and the processes generating them • Historical geology - seeks an understanding of the origin of Earth and its development through time; chronology of events

4. Geologic time • Accurate dates to events in Earth history • Absolute dating • Relative dating and the geologic time scale • Relative dating means that dates are placed in their proper sequence or order without knowing their age in years • The magnitude of geologic time • Involves – millions or billions of years • Geological processes operate • Gradually over periods as much as millions of years • Episodic in events that may last only seconds to minutes

5. Geologic timescale Age in millions of years

6. Early evolution of Earth • Origin of planet Earth • Earth and the other planets formed at the ~same time from interstellar dust • Nebular hypothesis • Layered structure developed by chemical segregation early in the formation of Earth

7. A view of Earth • Earth’s four spheres • Hydrosphere • Atmosphere • Biosphere • Solid Earth

8. Earth as a machine • Internal forces • Powered by heat from the interior • Leads to convection in the earth • Moves plates on the earth surface • Produce volcanoes, earthquakes, and mountains • External forces - Powered by the Sun that drives external processes in the • Atmosphere • Hydrosphere • At Earth’s surface

9. Earth’s surface has two principal divisions • Continents • Ocean basin

10. Theworkings behind the scene • Surface features, like oceans, mountains and others, are the product of internal workings of the earth

11. Earth’s internal structure • “Layercake” Earth • Crust • continental • oceanic • Mantle • upper • lower • Core • outer • inner

12. Earth’s internal structure • Mechanical Subdivision of the upper Earth • Lithosphere (rigid) • Asthenosphere (ductile, plastic) • Mesosphere

13. Earth’s Surface • Earth’s crust broken into rigid plates • 7 major plates • Where plates meet are called plate boundaries • Three types of plate boundaries

14. Plate Boundaries • Divergent (constructive) boundary – plates move apart, resulting in upwelling of material from the mantle to create crust • Convergent (destructive) boundary – plates move towards each other; subduction of oceanic plates or collision of two continental plates • Transform (conservative) boundary– plates move along each other without either generating new lithosphere or consuming old lithosphere

15. Dynamic Earth • The theory of plate tectonics • Theory, called plate tectonics, has now emerged that provides geologists with the first comprehensive model of Earth’s internal workings • The theory of plate tectonics • Involves understanding the workings of our dynamic planet • Began in the early part of the twentieth century with a proposal called continental drift – the idea that continents moved about the face of the planet

16. 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

17. There are three rock classes • Igneous (magmatic) rocks • Sedimentary rocks • Metamorphic rocks

18. Igneous Rocks • formed from a magma through crystallization either at or beneath the surface • examples: lava flows, granite, basalt, pumice Igneous rocks Cooling + Crystallization Lava Magma Melting

19. Sedimentary Rocks Transport Sediment Deposition or Precipitation Cementation + Compaction (Lithification) • formed through deposition of solid particles or through precipitation • examples: sandstone, claystone, limestone Sedimentary rocks

20. Metamorphic Rocks • formed through metamorphic transformation due to heat and pressure • examples: schist, slate, marble Heat + Pressure (Metamorphism) Compression Heat Metamorphic rocks

21. The science of Geology • Some historical notes about geology • The nature of Earth has been a focus of study for centuries • Catastrophism– earth changes by large events like floods, eruptions, etc. • Uniformitarianism – present is key to past; processes same through time, only rates have changed

22. The nature of scientific inquiry • 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 “facts” through observation and measurements

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

24. The nature of scientific inquiry • Scientific methods • Scientific method involvesgathering facts through observations and formulation of hypotheses and theories • There is no fixed path that scientists follow that leads to scientific knowledge