PLATE TECTONICS
 Earth consists of a solid, mostly iron inner core; a liquid, mostly iron outer core; a rocky, plastic mantle; and
a rocky, brittle crust.
 There are two different types of crust – oceanic (dense) and continental – that have very different
characteristics.
 The lithosphere is the solid outer shell of the Earth, composed of the uppermost portion of the mantle. The
Earth’s lithosphere is divided into plates that are in motion with respect to each other.
 Plate motion occurs as a consequence of convection in Earth’s mantle. Plate tectonics is driven by
convection in the mantle.
 Most geologic activity (e.g., earthquakes, volcanoes, and mountain building) occurs as a result of relative
motion along plate boundaries.
 Relative plate motions and plate boundaries are convergent (subduction and continental collision), divergent
(sea floor spreading), or transform.
 There are two different types of crust (oceanic and continental) that have very different characteristics
 Ocean crust is relatively thin, young, and dense. Continental crust is relatively thick, old, and less dense.
 Continental drift is a consequence of plate tectonics.
 Hot spot volcanic activity, such as volcanic islands, is exceptional in that it is not related to plate boundaries.
 An earthquake is a shaking of the Earth’s crust caused by a release of energy. Earthquake activity is
associated with all plate boundaries.
 Major features of convergent boundaries include collision zones (folded and thrust-faulted mountains) and
subduction zones (volcanoes and trenches).
 Major features of divergent boundaries include mid-ocean ridges, rift valleys, and fissure volcanoes.
 Major features of transform boundaries include strike-slip faults.
 A fault is a break or crack in Earth’s crust along which movement occurs
 Many types of faults occur due to the movement of plates.
 Most active faults are located at or near plate boundaries. Earthquakes result when movement occurs along
a fault.
 When rocks are compressed horizontally, their layers may be deformed into wave-like forms called folds.
This commonly occurs during continental collisions.
 A volcano is an opening where magma erupts onto Earth’s surface. Most volcanic activity is associated with
subduction, rifting, or sea floor spreading.
 There are three different types of volcanoes based on the structure of their cones and the type of ejecta that
caused them to form. Shield volcanoes are formed when large amounts of lava spill from a vent and spread
widely. Cinder cones build up when mostly tephra erupts from a vent and falls back to Earth around the
vent. Composite volcanoes form when both lava and tephra erupt. The materials pile up in alternating
layers and form a towering, cone-shaped mountain.
 Virginia has five physiographic provinces produced by past tectonic and geologic activity. Each province
has unique physical characteristics resulting from its geologic past. The five physiographic provinces of
Virginia are Coastal Plain, Piedmont, Blue Ridge, Valley and Ridge, and Appalachian Plateau.
 The Coastal Plain is a flat area underlain by young, unconsolidated sediments. These layers of sediment
were produced by erosion of the Appalachian Mountains and then deposited on the Coastal Plain.
Virginia’s Coastal plain consists of young unconsolidated sediments eroded from the western higher
elevations.
 The Piedmont is an area of rolling hills underlain by mostly ancient igneous and metamorphic rocks. The
igneous rocks are the roots of volcanoes formed during an ancient episode of subduction that occurred
before the formation of the Appalachian Mountains.
 The Blue Ridge is a high ridge separating the Piedmont from the Valley and Ridge province. The billionyear-old igneous and metamorphic rocks of the Blue Ridge are the oldest in the state. Some metamorphism
of these rocks occurred during the formation of the Appalachian Mountains.
 The Valley and Ridge province is an area with long parallel ridges and valleys underlain by ancient folded
and faulted sedimentary rocks. The folding and faulting of the sedimentary rocks occurred during a
collision between Africa and North America. The collision, which occurred in the late Paleozoic era,
produced the Appalachian Mountains.
 The Appalachian Plateau has rugged, irregular topography and is underlain by ancient, flat-lying
sedimentary rocks. The area is actually a series of plateaus separated by faults. Most of Virginia’s coal
resources are found in the plateau province.
ROCKS/MINERALS
 A mineral is a naturally occurring, inorganic, solid substance with a definite chemical composition and
structure. Minerals may be identified by their physical properties such as hardness, color, luster, and streak.
 Some major rock-forming minerals are quartz, feldspar, calcite, and mica. Ore minerals include pyrite,
magnetite, hematite, galena, graphite, and sulfur.
 The major elements found in Earth’s crust are oxygen, silicon, aluminum, and iron. The most abundant
group of minerals is the silicates, which contain silicon and oxygen.
 Minerals are important to human’s health and welfare. Important minerals and ores and their uses are
summarized in this table (for student awareness only).
Name of mineral/ore
Use(s)
Quartz (mineral)
Glass, watches
Feldspar (mineral)
Toothpaste
Calcite (mineral)
Neutralizing acids
Mica (mineral)
Lampshades, insulation
Pyrite (ore)
Iron ore
Magnetite (ore)
Iron ore
Hematite (ore)
Iron ore
Galena (ore)
Lead
Graphite (ore)
Lubricant
Sulfur (ore)
Rubber, medicines
Bauxite (ore)
Aluminum
 Most rocks are made of one or more minerals.
 Igneous rock forms from molten rock that cools and hardens either below or on Earth’s surface.
 Extrusive igneous rocks have small or no crystals resulting in fine-grained or glassy textures. Extrusive
igneous rocks include pumice, obsidian, and basalt.
 Intrusive igneous rocks have larger crystals and a courser texture. Intrusive igneous rocks include granite.
 Sedimentary rocks may either form from rock fragments or organic matter bound together or they are
formed by chemical precipitation. Sedimentary rocks are clastic or chemical. Clastic sedimentary rocks are
made up of fragments of other rocks and include sandstone, conglomerate, and shale. Non-clastic
sedimentary rocks include limestone and rock salt.
 Metamorphic rocks form when any rock is changed by the effects of heat, pressure, or chemical action.
Metamorphic rocks can be foliated or unfoliated (non-foliated). Foliated metamorphic rocks have bands of
different minerals. Slate, schist, and gneiss are foliated metamorphic rocks. Unfoliated metamorphic rocks
have little or no banding and are relatively homogeneous throughout. Marble and quartzite are unfoliated
metamorphic rocks.
 In Virginia, major rock and mineral resources include coal for energy, gravel and crushed stone for road
construction, and limestone for making concrete.
Name of rock
Use(s)
Coal (sedimentary)
Gravel/crushed stone (all)
Limestone (sedimentary)
Granite (igneous)
Energy
Road construction
Concrete
Building materials
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Pumice (igneous)
Lava soap abrasion
Quartzite (metamorphic)
Building materials
Slate (metamorphic)
Roofing, pool tables
Nonrenewable energy resources include fossil fuels and minerals. Renewable resources include vegetation,
sunlight and surface water. Renewable resources can be replaced by nature at a rate close to the rate at
which they are used. Water is a renewable resource.
WEATHERING & EROSION
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Weathering, erosion, and deposition (sedimentation) are interrelated processes that form a cycle of forces
that wear down and build up the Earth’s surface.
Water is continuously passed through the hydrologic cycle.
Fresh water is necessary for survival and most human activities.
Earth’s fresh water supply is finite.
Soil is one of man’s most valuable resources.
Factors – speed, volume, slope influence cutting ability – meanders.
Weathering is the process by which rocks are broken down chemically and physically by the action of
water, air, and organisms.
Erosion is the process by which Earth materials are transported by moving water, ice, or wind.
Deposition is the process by which Earth materials carried by wind, water, or ice settle out and are
deposited.
Weathering, erosion, and deposition are interrelated processes.
Weathering accelerates erosion and thus increases the rate of deposition.
The potential for erosion is greatest in areas of high relief.
The potential for deposition is greatest in areas of low relief, especially in standing water and in the ocean.
Permeability is a measure of the ability of a rock or sediment to transmit water or other liquids.
A substantial amount of water is stored in permeable soil and rock underground.
Water does not pass through impermeable materials.
Geological processes, such as erosion and human activities (such as waste disposal), can pollute water
supplies.
The three major regional watershed systems in Virginia lead to the Chesapeake Bay, the North Carolina
Sounds, and the Gulf of Mexico.
Karst topography is developed in areas underlain by carbonate rocks, including limestone and dolomite.
Where limestone is abundant in the Valley and Ridge province of Virginia, karst topography is common.
Karst topography forms when limestone is slowly dissolved away by slightly acidic groundwater. Karst
topography includes features like caves and sinkholes.
Soil is formed from the weathering of rocks and organic activity. Soil is loose rock fragments and clay
derived from weathered rock mixed with organic material.
Running water is the major cause of erosion.
Down slope movement of Earth materials is caused by gravity.
Features of erosion and deposition caused by waves include deltas, beaches, and sandbars.
Features of erosion and deposition caused by glaciers include U-shaped valleys, lakes, and moraine.
Features of erosion and deposition caused by wind include blowouts, dunes and loess.
Virginia’s coast line is shaped by the action of waves.
The composition and structure of soil is dependent on the resources, topography and climate.
Explain the types of deposition specific to streams and rivers (such as alluvial fans and deltas).
 Sedimentary rocks- horizontal layers, contain fossils
 Igneous rocks: Extrusive-cools fast-small crystals (fine) no crystals (glassy)
Intrusive-cools slow-large crystals (coarse to very coarse)
 Metamorphic rocks: banding-distorted structure-more dense.
 Mineral properties depend on internal arrangement of atoms.
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Porosity (amount of holes) - size doesn’t matter (when sorted)
Permeability (holes connected) – the bigger the particle size, the faster water goes through
Gravity is behind all erosion. (wind, running water, glaciers, ocean waves)
Capillarity (movement upward) – increases as particle size decreases
Streams are the number one agent of erosion.
Stream velocity depends on slope and discharge (amount of water in stream)
Velocity is faster on outside of meander bend-erosion occurs there and it is deepest.
Heavy-dense-round particles settle out first in water.
Graded bedding (vertical sorting) biggest sediments on the bottom.
Horizontal sorting - large particles settle out first (stream slows down when entering a larger body of water)
Glacial sediments are unsorted, scratched, U shaped valley and can carry boulders.
Stream deposits are sorted, round, smooth, V shaped valley. (abrasion)
Ground Water/Erosion
 Porosity (percentage of empty space) does NOT depend on particle size.
 Permeability, the ability to flow through ground material, pores must be connected. As particle size
increases, permeability also increases.
 Capillarity, Upward movement of water through the ground depends on surface area. As Particle size
decreases, capillarity increases.
 Gravity is the main FORCE behind all erosion.
 weathering is the breakdown of rock into sediments
 erosion is the transporting of those sediments
 RUNNING WATER (streams, rivers) is the number 1 AGENT of erosion in NYS.
Deposition
 Water and wind create sorted deposits of sediments. Gravity and Glaciers form unsorted deposits of
sediments.
 A common glacial deposit is called a moraine. Glacial deposits are unsorted.
 Stream velocity depends on SLOPE and DISCHARGE (the amount of water moving through the stream
at any one time). In a meander, velocity is greater (therefore erosion is greater also) on the OUTSIDE
of the curve.
 Streams and rivers carve a V-shaped valley. Glaciers carve a U-shaped valley.
 Heavy-Dense (large) particles settle to the bottom of a calm body of water faster.
 Colloids (clay-sized particles) remain suspended in bodies of water for long periods of time.
 In graded bedding (vertical sorting) the largest sediments are on the bottom.
Minerals and Rock
 Sedimentary rocks (strata) form (flat) horizontal layers.
 Igneous rock (fire-formed) are classified by texture (grain size). Coarse (large) grains = Intrusive (cooled slowly below surface). Fine (small) grains = Extrusive (cooled quickly). Glassy (no visible
crystals) = Extrusive.
 Metamorphic Rock – changed by heat and/or pressure. Shows banding/foliation (stripes) and distorted
structure. Higher density, very resistant rock.
 The formation of igneous rock causes contact metamorphism. Extrusion – bottom only affected,
Intrusion – top and bottom affected.
 All minerals properties are due to the internal arrangement of the atoms.
 Silicon and oxygen form earth’s basic mineralogical structural unit – the tetrahedron.
The Dynamic Crust
 Subsidence – the sinking of the crust
 Uplift – the lifting of the crust (Forms Mountains...)
 Earth’s plates move due to convection currents in the upper-mantle (asthenosphere)
 At the Mid-Ocean ridges (spreading center) new crust is created, age of the rock increases as distance
from the ridge increases. Divergent Plate Boundary
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Ocean trenches (subduction zone) where old crust is destroyed. Convergent Plate Boundary
P-waves travel faster than S-waves.
P-waves travel through solids and liquids.
S-waves travel through solids only (can’t go through the outer core).
Need a minimum of three (3) seismograph stations to determine the location of an epicenter.
Geologic History
Undisturbed rock – oldest layer is on the bottom (superposition).
Intrusions and faults are younger than the rock they cut through.
Unconformity: buried erosional surface – a gap in the rock record.
Carbon 14 (14C) – dates recent organic (once living) remains up to 50,000years old.
*Radioisotope decay is constant and unaffected by environmental changes.
Landscape Development
 Landscapes are dependant on bedrock structure and climate.
 Arid landscapes – steep slopes, angular features.
 Humid Landscapes – smooth, rounded slopes and features.
 The Catskills ARE NOT mountains (dissected plateau – horizontal bedrock).
 The Age of the earth is 4.6x109 years old, 4.6 billion years old, 4,600 million years.
Earth Science Facts you MUST know:
1.
When you cut an object into pieces, you don’t change its density.
2.
The Altitude of Polaris is equal to the latitude of the observer.
3.
The Coriolis force deflects currents to the right in the northern hemisphere.
4.
Condensation = phase change from gas to liquid – remove heat energy. No temperature change.
5.
Freezing = phase change from liquid to solid – remove heat energy. No temperature change.
6.
Boiling (vaporization) = liquid to gas – add heat – needs the most energy. No temperature change.
7.
There is no temperature change during a phase change (se 4, 5, and 6).
8.
Low Pressure = lousy, cloudy, humid weather, rising air currents, counterclockwise and convergent
circulation.
9.
High Pressure = happy, cloudless, dry weather, sinking air currents, clockwise and divergent circulation.
10. Weather moves from west to east (northeast trend) in the United States.
11. Porosity is not affected by particle size.
12. Potential Evapotranspiration (Ep) depends on TEMPERATURE ONLY!
13. Minerals have different properties due to their internal arrangement of atoms.
14. Marine fossils (seashells…) on mountain tops indicate that the land has been uplifted.
15. The Equatorial regions receive 12 hours of daylight EVERYDAY.