CSET Requirement 3.1a: Compare the amount of incoming solar energy, the Earth’s internal energy, the energy used by society, and the energy reflected back to space.
Solar Energy
Because of the tilt of the Earth's axis, incoming solar radiation is not evenly distributed on the Earth's surface and seasonal changes occur. The Sun is not in the exact center of the Earth's orbit. During the Southern hemisphere summer the Earth is closer to the Sun than during the Northern hemisphere summer. The Earth is farthest from the Sun during the Southern hemisphere winter. As the Sun's electromagnetic radiation penetrates the Earth's atmosphere it is selectively absorbed and scattered by molecules of gases, liquids, and solids. The energy coming from the Sun to the Earth's surface is called solar insolation or shortwave energy.
Energy goes back to space from the Earth system in two ways: reflection and emission. Part of the solar energy that comes to Earth is reflected back out to space in the same, short wavelengths in which it came to Earth. The percentage of solar energy that is reflected back to space is called the albedo. Different surfaces have different albedos. Over the whole surface of the Earth, about 30 percent of incoming solar energy is reflected back to space. Ocean surfaces (26% albedo) and rain forests (15% albedo) reflect only a small portion of the Sun's energy. A cloud usually has a higher albedo than the surface beneath it, the cloud reflects more shortwave radiation back to space than the surface would in the absence of the cloud, thus leaving less solar energy available to heat the surface and atmosphere. A cloud can absorb radiation emitted by the Earth's surface and radiates in all directions.
Energy goes back to space from the Earth system in two ways: reflection and emission. Part of the solar energy that comes to Earth is reflected back out to space in the same, short wavelengths in which it came to Earth. The percentage of solar energy that is reflected back to space is called the albedo. Different surfaces have different albedos. Over the whole surface of the Earth, about 30 percent of incoming solar energy is reflected back to space. Ocean surfaces (26% albedo) and rain forests (15% albedo) reflect only a small portion of the Sun's energy. A cloud usually has a higher albedo than the surface beneath it, the cloud reflects more shortwave radiation back to space than the surface would in the absence of the cloud, thus leaving less solar energy available to heat the surface and atmosphere. A cloud can absorb radiation emitted by the Earth's surface and radiates in all directions.
Earth's Internal Energy
The Earth's internal heat source provides the energy for our dynamic planet, supplying it with the driving force for plate-tectonic motion, and for on-going catastrophic events such as earthquakes and volcanic eruptions. This internal heat energy was much greater in the early stages of the Earth than it is today, having accumulated rapidly by heat conversion associated with three separate processes, all of which were most intense during the first few hundred thousand years of the Earth's history: (1) extraterrestrial impacts, (2) gravitational contraction of the Earth's interior, and (3) the radioactive decay of unstable isotopes.
Most scientists believe that our solar system evolved from the accretion of solid particles derived from a large nebular cloud - the so-called Nebular Hypothesis. Under this scenario, proto-planet Earth would have grown over time from a barrage of extraterrestrial impacts, increasing its mass with each bombardment. As the proto-planet grew in size its increased gravitational field would have attracted even more objects its surface. The composition of these colliding bodies would have included metal-rich fragments, rocky fragments, and icy fragments. Although accretion was much more prevalent in the early stages of the Earth's history, these extraterrestrial collisions are still occurring today, exemplified by shooting stars and fireballs in the night sky, and by the occasional impact of larger bodies on the Earth's surface. Such particles travel at great velocities, typically ~30,000--50,000 km/hr, similar to that of the Earth as it rotates around the Sun. The very large amount of kinetic energy inherent in these moving bodies is instantly converted to heat energy upon impact, thus providing a component to the Earth's internal heat source.
In the early stages of planetary accretion, the earth was much less compact than it is today. The accretionary process led to an increasingly greater gravitational attraction, forcing the Earth to contract into a smaller volume. Increased compaction resulted in the conversion of gravitational energy into heat energy, much like a bicycle pump heats up due to the compression of air inside it. Heat conducts very slowly through rock, so that the rapid build up of this heat source within the Earth was not accommodated by an equally rapid loss of heat through the surface.
Radioactive elements are inherently unstable, breaking down over time to more stable forms. The unstable isotope Uranium-238, for example, will slowly decay to Lead-206. All such radioactive decay processes release heat as a by product of the on-going reaction. In its early stages of formation, the young earth had a greater complement of radioactive elements, but many of these (e.g., aluminum-26) are short-lived and have decayed to near extinction. Others with a more lengthy rate of decay and are still undergoing this radioactive process, thus still releasing heat energy. The greater complement of unstable elements in the early Earth thus generated a greater amount of heat energy in its initial stages of formation.
The heat buildup inside earth reached a maxim early in the Earth's history and has declined significantly since. The greater heat content of the early Earth was the product of (1) a greater abundance of radioactive elements, (2) a greater number of impacts, and (3) the early gravitational crowding. The initial accretion of particles resulted in a rather homogeneous sphere composed of a loose amalgam of metallic fragments (iron meteorites), rocky fragments (stony meteorites), and icy fragments (comets). However, the increased heat content of the early Earth resulted in melting of the Earth's interior, so that the young planet became density stratified with the heavier (metallic) materials sinking to the center of the earth, and the lighter (rocky) materials floating upward toward the surface of the earth. The very lightest volatile materials (derived from comets) were easily melted or vaporized, rising beyond the earth's rocky surface to form the early oceans and the atmosphere. We now have a differentiated earth due to melting and mobilization of materials driven by the earth's internal heat engine. This has resulted in the development of a series of concentric layers that are both density and compositionally stratified.
Most scientists believe that our solar system evolved from the accretion of solid particles derived from a large nebular cloud - the so-called Nebular Hypothesis. Under this scenario, proto-planet Earth would have grown over time from a barrage of extraterrestrial impacts, increasing its mass with each bombardment. As the proto-planet grew in size its increased gravitational field would have attracted even more objects its surface. The composition of these colliding bodies would have included metal-rich fragments, rocky fragments, and icy fragments. Although accretion was much more prevalent in the early stages of the Earth's history, these extraterrestrial collisions are still occurring today, exemplified by shooting stars and fireballs in the night sky, and by the occasional impact of larger bodies on the Earth's surface. Such particles travel at great velocities, typically ~30,000--50,000 km/hr, similar to that of the Earth as it rotates around the Sun. The very large amount of kinetic energy inherent in these moving bodies is instantly converted to heat energy upon impact, thus providing a component to the Earth's internal heat source.
In the early stages of planetary accretion, the earth was much less compact than it is today. The accretionary process led to an increasingly greater gravitational attraction, forcing the Earth to contract into a smaller volume. Increased compaction resulted in the conversion of gravitational energy into heat energy, much like a bicycle pump heats up due to the compression of air inside it. Heat conducts very slowly through rock, so that the rapid build up of this heat source within the Earth was not accommodated by an equally rapid loss of heat through the surface.
Radioactive elements are inherently unstable, breaking down over time to more stable forms. The unstable isotope Uranium-238, for example, will slowly decay to Lead-206. All such radioactive decay processes release heat as a by product of the on-going reaction. In its early stages of formation, the young earth had a greater complement of radioactive elements, but many of these (e.g., aluminum-26) are short-lived and have decayed to near extinction. Others with a more lengthy rate of decay and are still undergoing this radioactive process, thus still releasing heat energy. The greater complement of unstable elements in the early Earth thus generated a greater amount of heat energy in its initial stages of formation.
The heat buildup inside earth reached a maxim early in the Earth's history and has declined significantly since. The greater heat content of the early Earth was the product of (1) a greater abundance of radioactive elements, (2) a greater number of impacts, and (3) the early gravitational crowding. The initial accretion of particles resulted in a rather homogeneous sphere composed of a loose amalgam of metallic fragments (iron meteorites), rocky fragments (stony meteorites), and icy fragments (comets). However, the increased heat content of the early Earth resulted in melting of the Earth's interior, so that the young planet became density stratified with the heavier (metallic) materials sinking to the center of the earth, and the lighter (rocky) materials floating upward toward the surface of the earth. The very lightest volatile materials (derived from comets) were easily melted or vaporized, rising beyond the earth's rocky surface to form the early oceans and the atmosphere. We now have a differentiated earth due to melting and mobilization of materials driven by the earth's internal heat engine. This has resulted in the development of a series of concentric layers that are both density and compositionally stratified.
Energy Used by Society
Energy in forms other than food is also essential for the functioning of a technical society. For example, in the United States, many times more energy in the form of engine fuel goes into the agricultural enterprise than is obtained in the useful food Calorie content of the food produced. Prodigious amounts of energy are also used to power automobiles, heat homes, manufacture products, generate electricity, and perform various other tasks. In order for our society to
function in its present patterns, vast amounts of coal, natural gas, and oil are extracted from the earth and burned to provide this energy. To a lesser extent we also derive energy from hydroelectric plants, nuclear reactors, electric wind generators, and geothermal plants, and, of course, we all benefit enormously from the energy obtained directly from the sun.The fossil fuels: coal, natural gas, and oil, supply about 85% of the energy used
in the United States. These resources evolved hundreds of millions of years ago as plant and animal matter decomposed and was converted under conditions of high temperature and pressure under the earth’s surface into the hydrocarbon compounds that we now call fossil fuels. Since the beginning of the machine age, industrial societies have become increasingly dependent on fossil fuels. A hundred and fifty years ago, the muscular effort of humans and animals played an important role in the American economy, and firewood supplied most of the heat energy. Now less than one percent of our energy comes from firewood and we rely much less on the physical effort of people and animals.
function in its present patterns, vast amounts of coal, natural gas, and oil are extracted from the earth and burned to provide this energy. To a lesser extent we also derive energy from hydroelectric plants, nuclear reactors, electric wind generators, and geothermal plants, and, of course, we all benefit enormously from the energy obtained directly from the sun.The fossil fuels: coal, natural gas, and oil, supply about 85% of the energy used
in the United States. These resources evolved hundreds of millions of years ago as plant and animal matter decomposed and was converted under conditions of high temperature and pressure under the earth’s surface into the hydrocarbon compounds that we now call fossil fuels. Since the beginning of the machine age, industrial societies have become increasingly dependent on fossil fuels. A hundred and fifty years ago, the muscular effort of humans and animals played an important role in the American economy, and firewood supplied most of the heat energy. Now less than one percent of our energy comes from firewood and we rely much less on the physical effort of people and animals.