CLEAN > Teaching Climate & Energy > Teaching Energy > 2. Energy in Physical Processes

Energy Principle 2. Physical processes on Earth are the result of energy flow through the Earth system.

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Teaching this principle is supported by seven key concepts:

2.1 Earth is constantly changing as energy flows through the system. Geologic, fossil, and ice records provide evidence of significant changes throughout Earth's history. These changes are always associated with changes in the flow of energy through the Earth system. Both living and non- living processes have contributed to this change.
2.2 Sunlight, gravitational potential, decay of radioactive isotopes, and rotation of the Earth are the major sources of energy driving physical processes on Earth. Sunlight is a source external to Earth, while radioactive isotopes and gravitational potential, with the exception of tidal energy, are internal. Radioactive isotopes and gravity work together to produce geothermal energy beneath Earth's surface. Earth's rotation influences global flow of air and water.

2.3 Earth's weather and climate are mostly driven by energy from the Sun. For example, unequal warming of Earth's surface and atmosphere by the Sun drives convection within the atmosphere, producing winds, and influencing ocean currents.

2.4 Water plays a major role in the storage and transfer of energy in the Earth system. The major role water plays is a result of water's prevalence, high heat capacity, and the fact that phase changes of water occur regularly on Earth. The Sun provides the energy that drives the water cycle on Earth.

2.5 Movement of matter between reservoirs is driven by Earth's internal and external sources of energy. These movements are often accompanied by a change in the physical and chemical properties of the matter. Carbon, for example, occurs in carbonate rocks such as limestone, in the atmosphere as carbon dioxide gas, in water as dissolved carbon dioxide, and in all organisms as complex molecules that control the chemistry of life. Energy drives the flow of carbon between these different reservoirs.

2.6 Greenhouse gases affect energy flow through the Earth system. Greenhouse gases in the atmosphere, such as carbon dioxide and water vapor, are transparent to much of the incoming sunlight but not to the infrared light from the warmed surface of Earth. These gases play a major role in determining average global surface temperatures. When Earth emits the same amount of energy as it absorbs, its average temperature remains stable.

2.7 The effects of changes in Earth's energy system are often not immediately apparent. Responses to changes in Earth's energy system, input versus output, are often only noticeable over the course of months, years, or even decades.

What does this principle mean?

When students learn about Earth processes, they generally focus on the process itself, such as plate tectonics, tides or streamflow. Energy Principle 2 illustrates how all of Earth's processes are driven by energy. These flows of energy are often overlooked but in many senses energy transfer can be thought of as a the driving force of the Earth system.

This principle points out that most of the energy in the Earth system comes from just a few sources: solar energy, gravity, radioactive decay and the rotation of the Earth. Solar energy drives many surface processes such as winds, currents, the hydrologic cycle, and the overall climate system. Gravity makes rivers and other materials flow downhill and creates tides (from the Moon's gravitational pull). Radioactive decay creates heat in the Earth's interior, while Earth's rotational forces influence currents of air and water.

This principle has considerable crossover with the Climate Literacy Principles 1 and 2. Climate Literacy Principle 1 focuses on the Sun as the primary source of energy for Earth's climate system, while Climate Literacy Principle 2 explains that greenhouse gases affect the energy balance of the Earth. Carbon dioxide and other greenhouse gases trap outgoing radiation that would otherwise exit the Earth system, thus warming the atmosphere. It also summarizes the carbon cycle through different carbon sinks and sources.

Why is this principle important?

Most students easily understand how a fuel like gasoline adds energy to a system. But principle 2 addresses the energy that is inherent in the processes all around us and explains how different forms of energy are prevalent throughout the Earth.

In some cases these forms of energy are constant, such as the decay of naturally-occurring radioactive materials within the Earth. This process releases heat to Earth's interior, which helps to drive the motion of plate tectonics. In other cases humans can affect the energy balance within the Earth system. One example is the carbon cycle, which describes how carbon can move from one form to another. Carbon can exist in carbonate rocks (like limestone), or in the atmosphere, or in the molecules of biological organisms. Large scale burning of fossil fuels is removing organic carbon from underground storage and releasing carbon dioxide into the atmosphere.

Related Pedagogic Method

Teaching about the early Earth

Another important aspect of this principle is that it addresses the evolution of the Earth's energy balance. Over the course of geologic time there have been drastic changes in the flow of energy through the Earth. For example, the Earth was entirely molten early in its geologic history and was covered in ice during the PreCambrian period. The Sun was once 30% dimmer than it is today. These dramatic changes illustrate how changing energy flows through the Earth system have altered the course of Earth's history. Presently humans are changing Earth's energy balance by increasing concentrations of greenhouse gases in the atmosphere. By examining changes in energy flow, students can appreciate how the planet has evolved and how humans are altering the balance over time.

What makes this principle challenging to teach?

This principle is subtle. It is far easier to grasp a familiar, observable physical process than it is to comprehend the energy that drives it. However, teachers can use this principle to reinforce the concepts in Energy Principle 1, and can point out the many places in which energy is the driver for a physical process, such as how energy flow affects weather and climate. Effective teaching of this principle will involve the students in using a systems approach to understand the interconnectedness between Earth's various systems.

Strategies for teaching this principle

This principle is largely about physical processes and flows of energy through the Earth system. This principle can be embedded in lessons about Earth processes so that students gain familiarity with the idea that energy is an integral part of nearly all processes on Earth. Teaching the energy flow in systems is one way to encourage systems thinking in students.

For middle school students, these dynamic processes can be illustrated by animations, videos and role-playing activities. Global Energy Balance is an animation that illustrates different pathways for incoming and outgoing radiation. Similarly, this Carbon Cycle interactive graphic outlines the carbon cycle, with clickable text boxes that explain and elaborate each component.

As with Energy Principle 1, concept sketching can be used for students to draw the flow of energy from one part of the Earth system to another. Incorporating animations and interactive visualizations into activities that include energy flow offer another pedagogic pathway.

High school students may benefit from learning this principle with a systems-based approach. Students may be more able to trace the flow of energy within a given part of the Earth system. For example, what form(s) of energy drive the atmosphere and the climate system? Students can trace the ways that solar energy enters the Earth system and the multitude of effects driven by this energy. Other examples of energy flow that lend themselves to a systems-based approach are processes at the interior of the Earth or the carbon cycle.

The Earth is a System visualization helps explain why understanding Earth as an integrated system of components and processes is essential to science education. In the Star Power! activity students estimate the energy output of the Sun by doing a simple experiment and discover how much energy sunlight provides to Earth and the role of the Sun in the Earth system. The video Striking a Solar Balance uses colorful animations to illustrate Earth's energy balance.

Related teaching materials

Teaching Systems Thinking for college-level students

Teaching Complex Systems with STELLA

College students will study physical processes as part of courses in geology, oceanography, atmospheric science or environmental science. In the context of these courses, students will be able to understand that energy drives Earth processes, and they can also begin to quantify flows of energy within and between various systems. The activity Modeling Earth's Energy Balance uses the STELLA box modeling software to determine Earth's temperature based on incoming and outgoing radiation, albedo, and a complex atmosphere with latent and sensible heat fluxes.

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