Chapter 1.3

The Energy Cycle

The Energy Cycle• The movement of energy into and out of

the Earth system.

• Different than the previous cycles we have learned about.

• More like a scale.– When you measure on a scale you want the

two sides to balance.– What is on one side should equal what is on

the other side.

The Energy Cycle Continued…

• The amount of energy entering a system should equal the amount of energy leaving a system.– If a system were to take in more energy than it

released, the system would increase in temperature.– If it released more energy than it took in,

temperatures would decrease.

• Because of this balance-scale nature, scientists refer to the energy cycle as the energy budget

• There are 3 main sources of energy in the energy budget: solar energy, geothermal energy, and tidal energy.

Solar Energy

• Most of the energy that enters the Earth system(99.985%) system comes from the Sun.

• Solar energy drives the winds, ocean currents, and waves.

• It is also the source of the energy that causes rocks to weather and soil to form.

Geothermal Energy

• Heat from within the Earth (0.013%)

• Geothermal energy is responsible for driving the tectonic plates, powering volcanoes, geysers and earthquakes, and also contributes to rock formation.

Tidal Energy

• Smallest part of the energy budget (0.002%)

• Resuts from the sun and moon’s pull on the Earth’s oceans.

• Powerful enough to slow Earth’s rotation because of the “tidal bulge”.

Maintaining the Balance

• Incoming energy must go somewhere.• About 40% of it is reflected back into

space.• Albedo

– The percentage of energy that is reflected without being changed.

– A forest has a low albedo (5-10% reflected).– A snow field has a high albedo (80-90%

reflected).

The Laws of Thermodynamics

• Energy follows predictable rules that explain what it will do.

• Thermodynamics is the branch of physics that deals with how heat energy is converted into other forms of energy.

• The laws of thermodynamics deals with how energy will flow.

First Law of Thermodynamics

• Energy can never be created or destroyed, only changed from one form to another.

• Example)– Solar energy is stored in plants which die and

eventually become fossil fuels.– Fossil fuels are burned at electrical power

plants and generate electricity, which can then power a light bulb.

Second Law of Thermodynamics

• When energy changes, it is converted from a more useful, more concentrated form to a less useful, less concentrated form.

• Unlike water which can convert from liquid to solid back to liquid without harm, energy cannot be recycled completely.

• Some energy will always be lost, usually in the form of heat.