Download Intro to Geology

Intro to Physical Geology (EAR 110)
What is Geology?
… the study of Earth
Two Divisions:
1. Physical geology  minerals, rocks, Earth processes
2. Historical geology  origin & evolution of continents,
oceans, atmosphere, & life
interdisciplinary
(astronomy, biology, physics, & chemistry)
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)
• 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.
A complex, dynamic system
SYSTEMS: atmosphere, biosphere, hydrosphere,
lithosphere, mantle, & core.
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)
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
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
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:
Basalt/Gabbro
more dense (3 g/cm3)
younger (180 my to pres)
Continental:
Andesite/Granodiorite
less dense (2.7 g/cm3)
older (up to 3.8 by)
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.
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
Plate Tectonic Theory
Lithosphere is divided into plates that fit like jigsaw
puzzle pieces across Earth’s surface.
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
Types of Plate Boundaries
CONVERGENT: (subduction zones)
**dense plates subduct under less dense plates
**subducted plate goes into the mantle & melts
DIVERGENT: (mid-ocean ridges)
**seafloor spreading  fractures open, molten mat.
from asthenosphere fills fractures
TRANSFORM FAULT:
plates move horizontally past one another w/out
consuming old lithosphere or generating new lithosphere
The Rock Cycle
…relates the formation of the major
rock groups to internal & external
processes
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
Above: Mudcracks
Lower Right: Bird tracks
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.