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Cycles & The Earth


    1.    Describe the characteristics of the water, carbon, energy, and nitrogen cycles.

    2.    Analyze how humans interact with the different cycles.

Key Terms:

    cycle        water cycle        evapotranspiration        carbon cycle        energy cycle        solar energy        geothermal energy        tidal energy


As we discussed earlier, Earth functions as a closed system.  In order for the system to continue to thrive the Earth must cycle its resources so that it can renew its supply of needed constituents such as water, carbon, nitrogen and energy.

The Water Cycle

(www.athensclarkecounty.com/.../ images/Water%20Cycle.png)

As you can see from the above image there are many paths for the water cycle.  Here is one scenario.

The sun heats up a body of water causing evaporation
The water vapor rises into the atmosphere and condenses as it cools forming clouds
When the water content in the clouds exceeds the capacity to hold the water precipitation (rain) begins

Scenario 2

Water from precipitation or bodies of water seep into the ground where it is used by plants
The plants continually release water through their leaves through a process know as transporation or evapotransporation
The rest is the same as scenario 1


The Carbon Cycle:










(users.rcn.com/.../BiologyPages/ C/CarbonCycle.gif)

The carbon cycle is considered to b a biogeochemical cycle.  Bio because of the sugars and molecules that are made from it and geo from the CO2 that is produced as a result of cellular respiration and the burning of organic compounds.  Carbon is the building block of life.  

Atmospheric CO2

Primarily removed by plants, algae, phytoplankton, and phytobacteria via the process of photosynthesis
Additional amounts of CO2 are dissolved in large bodies of water (oceans)
A small amount combines with water vapor to become acid rain

CO2 Production

Nearly all living things produce CO2
Decaying organisms will release CO2
The combustion of organic materials releases large amounts of CO2
The eruption of volcanoes is another source contributing to atmospheric CO2

The Nitrogen Cycle:

(muextension.missouri.edu/explore/ images/wq0252art01.jpg)

Nitrogen is an important building block used in the formation of DNA and proteins. Nitrogen is contained in the waste of every living organism as well as in the decaying organic material plants and animals.  Nitrogen uptake is primarily via ingestion.  Nitrogen is returned to plants through the process of nitrogen fixation that is performed by bacteria involved in the breakdown of dead organic material.

The Energy Cycle:

(hyperphysics.phy-astr.gsu.edu/ .../imgbio/treecycle.gif)

Earth's energy cycles are often referred to Earth's energy budget.  If the Earth takes in more energy than it uses the climate on Earth will get warmer and if it releases more than the sun gives it will get cooler.  No matter where the energy comes from it is important to remember that the laws of thermodynamics apply to each situation.  (Energy is neither created nor destroyed, only change from one form to another.)  There are three main sources for Earth's energy.

1)    Solar Energy

Comes from the sun
drives the winds, ocean currents and the waves
causes rocks and the soil to weather
provides the energy necessary to drive the cycles of the Earth

2)    Geothermal Energy

From the Earth's core
drives the movement of Earth's tectonic plates
powers volcanoes and earthquakes

3)    Tidal Energy

Results from the moon's gravitational pull on the Earth
acts to slow the rotation of the Earth










Last modified: January 30, 2003