Welcome to GLG101C Introduction to Geology Fall 2004 Professor James Tyburczy
Department of Geological Sciences
	Chapter 1 Notes

Note: These notes are intended to give a brief overview of important topics in each chapter. They are not a substitute for reading the textbook or for actually attending class.

updated 27 Aug 2004

Here are a few fun and interesting web sites giving an overview of Geology and Plate Tectonics:

• Don't forget about the site connected with your textbook Press, Siever, Grotzinger and Jordan "Understanding Earth"
• Here's a good site from the University of California at San Diego
• Check out This Dynamic Earth: The Story of Plate Tectonics from the U S Geological Survey

Chapter 1. BUILDING A PLANET

Why study geology?

• Earth resources - oil, minerals, groundwater
• Natural Disasters/Geologic hazards - volcanoes, earthquakes, floods, landslides
• Understanding the world around you
• Protecting the global environment - groundwater, atmosphere/climate, waste disposal, mining

Basic themes throughout the course

• Earth as a system of interacting components or sub-systems
• Plate Tectonics as a unifying theory of Geology
• Changing Earth Systems through Geologic Time

The Scientific Method - observation, hypothesis, repeated testing of the hypothesis, theory

• Scientific Theory - coherent explanation of for some natural phenomenon that is supported by a large body of evidence. Make predictions, test predictions.

Uniformitarianism - 'The present is the key to the past' -

• Types of geological processes that shaped the Earth in the past are the same as those we can see and understand operating today

Origin of the Solar System and of the Earth

• Big Bang, Solar nebula, contraction, condensation of the planets - 10 -15 billion years ago
• Earth accretion, self-compression, heating, differentiation - Earth formed about 4.5 billion years ago
• Formation of the Moon - Giant impact of Mars-sized body very early in Earth history - 4.5 billion years ago

The Solar System

• Inner (Terrestrial) Planets - Mercury, Venus, Earth, Mars - 'rocky'
• Outer Planets - Jupiter, Saturn, Uranus, Neptune, Pluto - large, gaseous
• Other solar systems - about 90 extra solar planets discovered so far

Earth's interior - Planetary Differentiation

• Core - inner core is solid, outer core is liquid, both are mostly iron (Fe)
• Mantle - most of the Earth, made of solid silicates but convects (flows)
• Crust - thin skin on surface, silicates
• Atmosphere/Oceans - volcanic gases from Earth's interior or late stage coating from comets?

Elemental composition of the Earth

• Whole Earth - Iron (Fe) is most abundant, followed by Oxygen (O), Silicon (Si), and Magnesium (Mg)
• Earth's Crust - Oxygen (O) is most abundant, followed by Silicon (Si), Aluminum (Al), Iron (Fe), and Magnesium (Mg)

Earth's Heat Engines

• Internal Heat Engine of the Earth - heat from radioactive decay inside the Earth plus heat from accretion drives mantle convection, which is ultimately responsible for mountain building, earthquakes, volcanoes, and plate tectonics on the Earth's surface
• External Heat Engine - Solar energy provides energy for atmospheric circulation, weather, ocean currents, and the hydrologic cycle. Precipitation and runoff erode and disintegrate rocks, wear down mountains, form sediments

Earth as a system of interacting components

• Atmosphere
• Hydrosphere
• Lithosphere (orLithospheric plate) - major unit of plate tectonics, contains crust and uppermost mantle, rigid, about 100 km thick
• Asthenosphere - upper mantle below lithosphere, plastic, flows
• Deep Mantle
• Outer Core
• Inner Core
• Biosphere (Life is found in Atmosphere, Hydrosphere, Lithosphere)

Interacting Earth Systems

• Climate System - Atmosphere, Hydrosphere, Biospehre, Lithosphere - driven by solar energy (external energy)
• Plate Tectonic System - Lithosphere, Asthenosphere, Deep Mantle - driven by Earth's internal energy
• Geodynamo System - Outer core, inner core, Earth's magnetic field (internal energy)

Plate Tectonics - theory

• Lithospheric plate or lithosphere- major unit of plate tectonics, contains crust and uppermost mantle, rigid, about 100 km thick
• Asthenosphere - upper mantle below lithosphere, plastic, flows
• Crust/mantle boundary vs. lithosphere/asthenosphere boundary - crust-to-mantle is a difference in chemical composition (and mineralogy and rock type). Lithosphere-to-asthenosphere is a difference in strength

3 types of plate margins:

1. Divergent margin -spreading centers - mid-ocean ridges, form new oceanic lithosphere
2. Transform margin - plates slide by one another (ex. San Andreas)
3. Convergent margin - for example, subduction zone -> volcanism, mountains

Geologic Time - Darth is 4.5 billion (4,500,000,000 or 4.5 x 10^9) years old. Major events in the history of the Earth

• 4.5 billiion years (b.y) ago - Earth formed
• 4.0 b.y ago - heavy bombardment ends - stable crust is formed
• 3.5 b,y ago - earliest evidence for life - fossils of single celled bacteria
• 2.5 b.y ago - oxygen begins to be a major compoenent of the atmosphere - because photosynthesis is occurring - plant life
• 600 million years ago (m.y.) - first animals
• 543 m.y. ago - Biology's Big Bang - explosion of new life forms - earthworms, starfish, sand dollars, moluscs, insects, trilobites, first appear - snimals with hard, calcium-rich body parts appear.
• 65 m.y. ago - Major bolide impact causes a mass extinction and ends the age of the dinosaurs
• 5 m.y. ago - first hominids
• 120,000 years ago - humand first appeared