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The Earth -----------
Earth possesses an atmosphere, hydrosphere, lithosphere and biosphere.
It is a dynamic planet, with active volcanos and earthquakes.
The earth changes slowly through time, by weathering and erosion of the landscape, and by changes in the position of continents and ocean basins driven by plate tectonics.
Geology -------------
Geology, which is the science of the study of the earth, can be generally divided into two broad areas: physical geology (dealing with earth materials and processes) and historical geology (dealing with the origin and development of the earth through time and the evolution of life).
Geology is an applied science, built on principles of physics, chemistry, mathematics and biology.
The study of geology spans a wide range of scale, from the microscopic (composition and structure of minerals) to the megascopic (composition of planets).
Geologists also have a great appreciation of the 4th dimension (time), as the earth is very old (about 4.6 billion years).
Geologists and Earth Scientists ------------
What does a geologist do? Some very important things in support of a modern, industrialized society:
Exploration for minerals, oil, and gas for industry
Locating deposits of sand and gravel for building aggregate
Location of groundwater and areas of contamination
Identification of geologic hazards (eg. landslides, floods)
The Earth --------------------
Earth is the third planet in the solar system.
It is about 12,700 km in diameter, and is believed to have originated in a cloud of condensing gas and dust (the nebular hypothesis) and by planetary accretion.
Radiometric age dating of rocks shows that the earth is about 4.6 billion years old.
The Earth possesses an internal structure consisting of a core, mantle and crust. Each varies with respect to their density and composition.
Plate tectonics is an active and on-going process by which large, rigid segments of the outer portion of the earth (plates) are moving relative to one another - very, very slowly, through time.
Convergent type boundaries exist where the plates are colliding, such as in ocean trenches.
Divergent type boundaries exist where the plates are pulling apart, such as at mid-ocean ridges.
Transform type boundaries occur where plates slide past one another, such as along the San Andreas fault system in California.
Concepts of Geologic Time ------------------
An early view of geologic time was one based upon interpretation of the Bible. "Catastrophism" is a school of thought where proponents believe that the earth is very young. So large earth surface features (like the Grand Canyon) had to be carved through great and sudden catastrophies.
A more contemporary view of the age of the earth is based on the acceptance of the fact that physical laws have probably not changed through time, and that they operate today much as they did in the earth's distant past. Proponents of "uniformitarianism" believe in the uniformity of processes through time, and that earth surface features are the product of long term but very slow erosion. "The present is the key to the past!"
The Rock Cycle ----------------------
James Hutton and the rock cycle. KNOW THIS!!!!!
Igneous rocks originate from the crystallization of cooling magma or lava, on either the surface of the earth (extrusive) or deep underground (intrusive).
Sedimentary rocks consist of compacted and cemented pre-existing rock particles.
Metamorphic rocks have changed their form, through heat and pressure, from either igneous, sedimentary or metamorphic parent rock material.
Increasing world population is making demands on the earth's mineral resources, particularly to support a growing industrial civilization.
Discovery of new mineral resources is termed exploration geology, and this is the first part of the process of exploiting earth resources:
1. Prospecting - finding the ore
2. Mine development
3. Ore processing and milling
4. Smelting and refining
5. Mineral use
6. Reclamation
Concentration of minerals in the earth can occur in several ways:
1. hydrothermal deposition
2. magmatic processes
3. sedimentary processes
4. placers
5. residual deposits
Energy resources that are earth-derived include coal, natural gas, petroleum, and uranium.
Rocks are aggregates of one or more minerals.
Minerals are naturally occurring inorganic solids that posses a definite internal structure (crystalline) and have a specific chemical composition.
The silicate family of minerals is the largest group, and members of this group consist mostly of oxygen and silicon. The O and Si are bound by ionic bonds, and several fundamental silicate structures can result:
1. Isolated tetrahedra (ex. olivine)
2. Single chain (ex. augite)
3. Double chain (ex. hornblende)
4. Sheet (ex. mica)
5. Framework (ex. quartz)
In order to identify minerals in the lab, one must use several mineral properties:
1. Crystal Form
2. Luster
3. Color
4. Streak
5. Hardness
6. Cleavage
7. Fracture
8. Specific Gravity
9. Other (eg. magnetic)
Igneous rocks are aggregates of mineral grains (may include glass) which are formed from melted material through crystallization.
Magma = intrusive molten material
Lava = extrusive molten material
Important textures (controlled by location and rate of cooling):
Coarse-grained textures suggest long term cooling deep underground (intrusive).
Fine-grained textures suggest short term cooling on the earth's surface (extrusive)
Porphyritic textures suggest more complex environments of crystallization.
Vesicular textures are created due to escaping gases, primarily in lavas.
Glassy textures are created due to instant quenching and/or dry magmas.
Bowen's Reactions Series summarizes the order of crystallization of minerals from a basaltic magma. How do the silicate structures discussed above relate to this sequence?
Igneous Rock Classification ---------------
Igneous rocks are classified by both their chemical composition (mostly by their relative silica content) and by their texture.
Know the similarities and differences between the following igneous rock types:
Basalt and gabbro
Granite and rhyolite
Andesite and diorite
Intrusive Igneous Rock Occurrence --------------------
The occurence of intrusive igneous rocks is dictated by their emplacement and crystallization at depth, within the earth's crust, and are generally termed plutonic. If igneous rocks are created at the earth's surface, they are termed volcanic, and are discussed in a later section below.
Plutonic structures (intrusive rock bodies) in the crust are termed batholiths, dikes, sills based on their size and geometry and their relationship to the surrounding rock.
