geology scientific method observation (collecting data) develop hypothesis based on observations (educated guess) test hypothesis (more data, more experiments, challenge hypothesis) theory (hypothesis that’s been tested and and sometimes revised) model (law/principle/paradigm) Center of Geology/Main Paradigm= Plate Tectonics
The Big Bang Theory 1. Origin of the Universe 2. Estimated to be 13.7 Billion years ago 3. Condensation of our Solar System estimated to be 4.56 billion years ago 4. Age of earth: about 4.6 billion years old. Oldest rocks found are 4 (Ga) 5. We know this from meteorites and the moon
Nebular Hypothesis 1. A nebula spins faster and flattens causing it to become hotter and hotter which eventually leads to the production of hot-nuclear fusion. 2. Gas condenses and collides with dust to for planetesimals (baby planets) 3. Planetesimals collide, stick together, and form planets
The Moon 1. Impact of Mars-sized body with proto-earth at about 4.5Ga, Collision tilted earth’s spin axis and ejected material that formed the moon. 2. Moon is trapped by earth’s gravitational pull.
Differentiation of the Earth 1. Iron and nickel form core 2. Light materials move to top 3. Crust, mantle, outer core, inner core.
Characteristics of Earth 1. Earths density is higher than most rocks, so there must be denser material deeper in Earth. 2. Meteorites- pieces of broken planets -Stony (Mantle material, 3 g/cm3) -Fe-Ni (Core material, 8 g/cm3)
3. Hypothesis Fe and Ni sunk inward due to gravity
4. Test hypothesis by seismology
5. Seismic Waves -Compressional (P-waves; pass through solid, liquid, gas) -Shear (S-waves; pass through solid only) -Seismology is one of the primary tools geologist use to study the earth’s interior
Vocabulary: know about these words, not definition
-Crust
-Mantle- most of planet, highest-density silicate minerals (O, Si, Mg, Fe, Ca, Fe)
-Inner Core
-Outer Core
-Lithosphere (how differs from crust)- crust + top mantle (100km) cold, strong, rigid
-Asthenosphere- weaker part of upper mantle:hot, weak, ductile
-Plate Tectonics
Composition of the Earth 1. Mantle- 99% of the earth is made up of 8 elements: Fe, Si, O, Mg, Al, Ca, Ni, and Sulfur. 2. Inner core- mostly Fe and Ni. solid bc of pressure, density of 13gm/cm^3 3. Outer Core- Ni, S, O, and mostly Fe. liquid bc of temp. density of 11gm/cm^3 4. Mantle- O, Si, Al, Fe, Mg, Ca 5. Crust- all
Crust 1. Less dense continental crust floats on denser mantle 2. Continental crust (2.8 g/cm3) is less dense than ocean crust (3.0) 3. Low-density silicate minerals (O, Si, Al, K) 4. Continental crust
-40 Km thick
5. Oceanic crust
-7 km thick
6. Less dense continental crusts floats higher on denser mantle than oceanic crust
7. Moho discontinuity: boundary of crust and mantle Thursday, December 11, y
crust, mantle, core lithosphere, asthenosphere .. know that the earth is broken up into these things
-geotherm (temperature gradient)- temp gradient is largely responsible for plate tectonics
mantle convection— plates interact in 3 ways divergent-move away convergent- pushed against one another- one goes down transform-slide past one another
as plates age (move away from the ridge) they cool and become denser. eventually they become denser than the underlying mantle, and sink.
Plate tectonics- lithosphere is broken into several semi-rigid plates that move over the asthenosphere in response to mantle convection. key terms-
1. moho
2. lithosphere
3. asthenosphere
4. convergent boundary
5. divergent boundary
6. transform boundary
Pangea= “all lands” proposed by Alfred Wegener in 1915 evidence for Pangea- distribution of rock assemblages and ages, fossils (Mesosaurus, Glossopteris), glaciation
Seafloor spreading seafloor bathymetry- rifts earthquakes showed the seafloor to be tectonically active along these rifts magnetism and age of the crust
Seafloor Magnetic Anomalies
D.H. Mathews and F.J. Vine (1963)
