Geology
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Geology (from Greek γη- (ge-, "the earth") and λογος ("logos", "word", "reason")) is the science and study of the solid matter of a celestial body, its composition, structure, physical properties, history and the processes that shape it. In this book, the term Geology will apply to the Earth in particular.
Geology can be split into two main branches: historical and physical. Historical geology attempts to understand the origins, composition, systems and changes of the Earth.
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[edit] History
According to the widely accepted Big Bang theory, the Universe began at some point in space and time around 13,700,000,000 years ago, as evidenced by the doppler effect observed in all stars and a 3 degree Kelvin background radiation observed elsewhere.
- In about 10E-43 seconds, physics became defined and gravity separated from other forces. The Universe was 10E32 K in temperature.
- At 10E-35 seconds, the Universe expanded to the size of a softball and the strong nuclear force separated. Energy turned into quarks and electrons and their anti-matter counterparts. The temperature was 1027 K.
- At 10E-6 seconds, quarks began to bind into protons and neutrons; matter and antimatter destroyed each other and the balance turned out to be in favor of matter. The Universe was about the size of our solar system and 1013 K hot.
- 1 second after its inception, the electromagnetic and weak nuclear forces appeared as the Universe cooled to 109 K.
- 3 minutes later, protons and neutrons fused into nuclei.
- After 100,000 years, the electrons and the nuclei came together to form atoms; photons separated from matter and there was light.
- In the next 1,000,000,000 years the Universe became clumpy as galaxies began to take shape.
- Ever since then, the Universe has cooled down to 3 K, galaxies have developed, generations of stars have passed, creating heavier elements, and life has appeared. Our galaxy, the Milky Way, contains about 200,000,000,000 stars and lies 1 million light years from its nearest neighbor.
- The solar system was formed around 4,600,000,000 years ago as dust collapsed into the protostar that was to become the Sun, and into planetesimals orbiting it. The inner planets, from Mercury to Mars, are solid because the solar winds have driven gases away and have a core; the outer planets are larger and consist of gas.
[edit] Structure and Composition of the Earth
The outermost layer of the earth is called the lithosphere (100-200km deep); it is followed by a plastic asthenosphere (150-400km deep). Independent of these classifications, the internal structure of the earth is divided into three main layers: the crust, the mantle and the core.
The crust, which is solid and mainly made up of silicates, can be divided into continental crust and oceanic crust. The continental crust ranges in thickness from 35-60km. It is andesitic in composition, with a Si02 composition of 57% by weight. 95% of crustal rocks are igneous and metamorphic, while only 5% are sedimentary. These range from granite near the surface to gabbro, deep down near the mantle. The oceanic crust is much thinner than the continental crust, with an average thickness of just 5km. It is denser than the continental crust and mainly composed of basaltic rocks, giving it a SiO2 content of 49% by weight. The atmosphere, hydrosphere and biosphere are often also considered to be part of the crust.
The mantle stretches from the base of the crust to approximately 2900km, and is divided into three zones: the upper mantle, the transition zone and the lower mantle. The upper mantle is rich in dunite, peridotite and eclogite rocks, and is heterogeneous (probably due to partial melting of mantle magmas). Magma is continuous extracted from the upper mantle. The transition zone, between the upper and lower mantle, is marked by polymorphic phase transition from spinel and pyroxene to ilmenite and rutile, then eventually to stishovite. In the transition zone, due to higher pressure at a greater depth, rocks have more closely packed structures than those in the upper mantle and crust. The lower mantle appears to be homogeneous, with even denser, very closely packed materials.
Physical properties of the earth's core suggest that it is made up mainly of iron and nickel allows. The outer core is solid, while the inner core is liquid. Physical properties of the core suggest that it is made up mainly of iron and nickel alloys.
[edit] Plate Tectonics
Because of the interactions between the lithosphere, the asthenosphere, and the mantle underneath, our planet's crust is governed by 'plate tectonics.'
Plate tectonics is a theory based on the principle of Uniformitarianism, which reads: "The Present is the Key to the Past." The earth in its current state is the result of natural processes operating over vast periods of time, and can be understood by watching the action of ongoing processes.
[edit] Volcanism
There are three(3) types of lavas formed by volcanoes. Mafic, Intermediate, and Felsic.
Mafic(Basaltic)
- %SiO2: < 50%
- %FeMg: 4%
- Temp: up to 1500C
- Viscosity: Low
- Eruptive Behavior: gentle
- Distribution: divergent plate boundries, hot spots, convergent plate boundries
Intermediate(Andesitic)
- %SiO2: ~60%
- %FeMg: ~3%
- Temp: ~1000C
- Viscosity: Intermediate
- Eruptive Behavior: explosive
- Distribution: convergent plate boundries
Felsic (Rhyolitic)
- %SiO2: >70%
- %FeMg: 2%
- Temp: 700C
- Viscosity: High
- Eruptive Behavior: explosive
- Distribution: hot spots in continental crusts (Yellowstone National Park), convergent plate boundries
