1. Intro to Physical Geology (EAR 110)

2. What is Geology? … the study of Earth
Two Divisions:
Physical geology  minerals, rocks, Earth processes
Historical geology  origin & evolution of continents, oceans, atmosphere, & life
interdisciplinary
(astronomy, biology, physics, & chemistry)

3. Why is Geology Important to You?
Minerals have practical daily uses.
(toothpaste, vitamins, drink cans, cosmetics, salt, pencil “lead”, jewelry, currency, ceramics, paints, fertilizers, lubricants, abrasives, etc.)
Informed decisions are essential.
(i.e., mineral rights, safety of water supply,
stream flooding, community planning boards,
communication to legislators enacting
environmental regulations)

4. Knowledge of geologic hazards lessens the severity of their impact.
Standard of living is dependent on the use of geologic materials. (i.e., Overuse of resources adversely affects balance of nature, culture, & environment.)
Sustainable development
insures future generations sufficient natural resources to maintain standard of living for a larger population.

5. A complex, dynamic system
SYSTEMS: atmosphere, biosphere, hydrosphere, lithosphere, mantle, & core.

6. 3 Physical Environments:
1. Solid Earth – core, mantle, & crust
2. Hydrosphere – dynamic mass of H2O
The Water Cycle
--evaporation from oceans into the atmosphere
-- precipitation onto land
-- water flows back into the oceans
3. Atmosphere – gaseous envelope around Earth 
(interaction b/w surface & atm.  WEATHER)

7. Characteristics of Earth’s Core
composed of Fe (minor Ni & other heavy elements)
inner core: solid, Fe-rich sphere
outer core: molten metallic layer
They’re compositionally similar.
Magnetic field  provided by circulation of the molten outer core

8. Characteristics of Earth’s Mantle
82% of Earth  ~2900km thick
located below the crust
behaves like a solid when EQs pass thru it, but can flow slowly (plastic)
Divided into regions:
Upper: (Asthenosphere) crust thru upper mantle (660km into Earth)
Lower: (Mesosphere) from a depth of 660km to the outer core

9. Characteristics of Earth’s Crust
LITHOSPHERE  rigid, solid
Thickness: Average = 15 km
3 km (~2mi) at ocean ridges
70 km (40 mi) in ancient mtn belts
Oceanic: Continental:
Basalt/Gabbro Andesite/Granodiorite
more dense (3 g/cm3) less dense (2.7 g/cm3)
younger (180 my to pres) older (up to 3.8 by)

10. Formulation of Theories
theory  speculative explanation; wild guess
theory (scientific)  coherent explanation supported by large body of evidence; validity of explanation testable by experiment
How are theories born?
The Scientific Method
Refinement occurs by further testing.

11. The Scientific Method 1. Collection of Data
 gather scientific facts thru observations & measurements
2.   Hypothesis formation
 theory vs. hypothesis?
3.   Tests of the hypothesis
 develop experiments for testing
4.   Acceptance, modification, or rejection of the hypothesis

12. Plate Tectonic Theory
Lithosphere is divided into plates that fit like jigsaw puzzle pieces across Earth’s surface.

13. Plate Tectonics Theory
Continental drift  Continents moved across Earth’s surface. (50 yrs+ for acceptance)
Plates float on asthenosphere as they move & they interact along their boundaries.
Plate movement is driven by the unequal distribution of heat w/in Earth.
1) major landscape features (mtns, valleys)
2) distributes natl. resources
3) distribution & evolution of the biosphere

14. Types of Plate Boundaries
CONVERGENT: (subduction zones)
**dense plates subduct under less dense plates
**subducted plate goes into the mantle & melts

15. DIVERGENT: (mid-ocean ridges)
**seafloor spreading  fractures open, molten mat. from asthenosphere fills fractures

16. TRANSFORM FAULT: plates move horizontally past one another w/out consuming old lithosphere or generating new lithosphere

17. The Rock Cycle
…relates the formation of the major rock groups to internal & external processes

18. James Hutton — Scottish physician
Uniformitarianism [late 1700s]
James Hutton — Scottish physician
… very intelligent …not able to convey his thoughts
“The present is the key to the past.”
**Laws that govern the physical, chemical, and biological processes occurring now on the earth, also operated in the past... (i.e., These processes are unchanging through time.)
Charles Lyell
Principles of Geology (mid 1800s)
**noted that processes may have been operating at varying rates in the past or that they may not have had the same significance as they do today

19. Above: Mudcracks
Lower Right: Bird tracks

20. Geologic Time Scale
19th century geologists arranged info from outcrops based on changes in biota thru time (relative age).
Radiometric dating (20th century) assigned absolute age dates to the sub-divisions.