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Chapter 18: Cycles of the Earth

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Hydrologic Cycle
The amount of water on Earth has been about the same since ∼4.0 billion years.
Reservoirs of Water
Oceans, lakes, rivers, and streams. Ice caps and glaciers. Atmosphere and clouds. Groundwater (in acquifers) and ground ice. Living organisms.
Modes of Water Movement
Precipitation (rain, snow, etc.), evaporation, sublimation, transpiration, flow due to gravity.
Ocean Currents
Redistribute solar heat in sea water across the Earth; affects Earth's weather and climate.
Gyres
Current systems involving return flow of cold water to lower latitudes; mainly occurs in large ocean basins.
Upwelling
Colder deep water flows up at coastal areas due to wind energy pushing surface water away from land.
Bottom Currents
Cold water from polar areas that flows down to sea floor and toward the equator; cold water is colder and more dense.
Saltiness of Water
Due to weathering of rocks on land, and transportation of dissolved elements into the sea; saltiness at present level since ∼3.5 billion years ago.
Removal of Salt from the Ocean
Evaporation of sea water causes saturation and then precipitation of salt crystals, organisms in the sea also take up dissolved minerals.
Residence Time in the Oceans
Each element in sea water stays there an average period of time depending upon how it is usually removed.
Na
PPM in ocean water = 10,800
Residence Time = 260 x 10⁶ yr
Ca
PPM in ocean water = 413
Reidence Time = 8 x 10⁶ yr
Cl
PPM in ocean water = 19,400
Reidence Time = infinite
Au
PPM in ocean water = 0.00005
Reidence Time = 4.2 x 10³ yr
K
PPM in ocean water = 387
Reidence Time = 11 x 10⁶ yr
Cu
PPM in ocean water = 0.003
Reidence Time = 5 x 10⁴ yr
Return of salt to the sea
Sediments of the ocean form layers of sedimentary rock that are pushed up into folded mountains, eroded away and transported to the ocean via rivers and streams; subduction may also result in melting of these sediments and chemical return to the ocean via volcanoes.
Ice Age
Periodic cycle of glacial and interglacial stages (intervals of geologic time).
Pleistocene
Ice age 4 m.y. to present
Pennsylvanian - Permian
Ice age 350-250 m.y. ago
Ordovician-Silurian
Ice age 460-430 m.y. ago
Proterazoic
Ice age 800-600 m.y. ago
Wisconsinian
Glacial stage 75,000 to 11,000 yr ago
Illinoisan
Glacial stage 265,000 to 125,000 yr ago
Kansan
Glacial stage 465,000 to 300,000 yr ago
Nebraskan
Glacial stage 1.8 m.y. to 500,000 yr ago
Effects of Glacial Stages
Sea level drops by ∼250 m due to loss of ocean water as ice caps and glaciers grow. Glaciers move across the land cutting deep U-shaped valleys; glaciers erode and transport vast amounts of soil and rock.
Effects of Interglacial Stages
Sea level rises and shoreline moves inland. Land rises due to removal of weight of ice caps and glaciers. Water takes over as main erosional agent on land; rivers and lakes are re-established.
Milankovitch theory of Ice Ages
Variations in Earth's rotation and orbit ake slight variations in total amount of solar radiation absorbed by Earth's atmosphere; when Precession, Obliquity, and Eccentricity work together.
Precession
Milankovitch factor. 23,000 year cycle in the wobble of the world's axis.
Obliquity
Milankovitch factor. Change in axial tilt over time from 21.5° - 24.5° over a 41,000 year cycle.
Eccentricity
Milankovitch factor. Change in the shape of the Earth's orbit caused by other planet's gravity (∼100,000 years).
Plate Tectonic Control on Ice ages
Glacal stages can occur only when continents are in a high latitude position wher ice caps and glaciers can build up on them; continental position can affect ocean and atmospheric circulation as well.
Weather
Short term variations in the state of the atmosphere at a given time and place.
Climate
Long pattern of weather for a given region.
Temperature
Weather variable that affect atmospheric density.
Pressure
Weather variable. Lateral variations cause movement of weather systems.
Low Pressure System
Warm, moist air.
High Pressure System
Cooler, dryer air.
Jet Streams
Boundary cones between pressure systems in the Earth's atmosphere.
Humidity
Water content in the air.
Cloudiness
Percent and type of clouds. Wind direction and strength (speed).
Atmospheric Circulation
The effect of rotation of Earth and solar heating. Six main circulation cells, 3 in each hemisphere.
Northern Hemisphere
Northeast trade winds prevailing westerlies, polar wind belt.
Southern Hemisphere
Southeastern trade winds, prevailing westerlies, polar wind belt.
Tropical Storms
Severe storms that start as low pressure systems over warm ocean water; have cyclonic movement wind 50 to 300 km/hr.
Gyres
Strong tropical storms of the Atlantic.
Typhoons
Strong tropical storms of the Pacific.
Tornadoes
Small scale, violent rotating funnels of air; winds 300 to 500 km/hr.
El Niño
4 to 7 year cycles of weather in Northern hemisphere; due to winds blowing across the Pacific, which affects water circulation patterns in the Pacific basin causing unusually warm waters in equatorial areas and much rain.
La Niña
4 to 7 year cycles of weather in Northern hemisphere; cold waters...dry conditions
Climate Cycles
Follows large scale reorganization of oceanic and atmospheric circulation (following tectonic plate movement and the growth of mountains. Accompany large changes in global average temperature.
Greenhouse World
Geologic times of high average global temperature.
Icehouse World
Geologic times of low average global temperature.
Igneous Rocks
Rocks that solidified from liquid rock (magma).
Sedementary Rocks
Rocks made of grains and crystals from other rocks; pre-existing rocks must be disintegrated and decomposed (rock weathering) to make materials (sediments) needed to make this type of rock.
Metamorphic Rocks
Rocks that form by solid-state changes in pre-existing rocks that have been heated and put under high pressure (but not melted).