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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.


Current systems involving return flow of cold water to lower latitudes; mainly occurs in large ocean basins.


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.


PPM in ocean water = 10,800
Residence Time = 260 x 10⁶ yr


PPM in ocean water = 413
Reidence Time = 8 x 10⁶ yr


PPM in ocean water = 19,400
Reidence Time = infinite


PPM in ocean water = 0.00005
Reidence Time = 4.2 x 10³ yr


PPM in ocean water = 387
Reidence Time = 11 x 10⁶ yr


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).


Ice age 4 m.y. to present

Pennsylvanian - Permian

Ice age 350-250 m.y. ago


Ice age 460-430 m.y. ago


Ice age 800-600 m.y. ago


Glacial stage 75,000 to 11,000 yr ago


Glacial stage 265,000 to 125,000 yr ago


Glacial stage 465,000 to 300,000 yr ago


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.


Milankovitch factor. 23,000 year cycle in the wobble of the world's axis.


Milankovitch factor. Change in axial tilt over time from 21.5° - 24.5° over a 41,000 year cycle.


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.


Short term variations in the state of the atmosphere at a given time and place.


Long pattern of weather for a given region.


Weather variable that affect atmospheric density.


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.


Water content in the air.


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.


Strong tropical storms of the Atlantic.


Strong tropical storms of the Pacific.


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).

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