Take an Imaginary Trip.


Think of a place on our planet that hasn’t been significantly disturbed by humans in a hundred years or more, a place that you might describe as a “wilderness area.” Envision yourself exploring the area—very carefully, since too much interference by humans might upset the delicate environment. What would you see? Shut your eyes. What would you hear or smell? How would the area feel?Depending on your choice, there could be many species or only a few. The vegetation could be thick or sparse. You might identify large animals, or have to search for small ones. But it’s inevitable that the organisms you find will be part of a delicate and dynamic balance; a system of energy and nutrient use that has been negotiated over many years of growth. You’ll experience an ecosystem. If you are standing (or floating) on the surface of the Earth, the energy that powers that ecosystem will have come from the sun. (Gravity provides additional energy for weather, and there are massive ecosystems at the bottom of the ocean with very different sources of energy, but that’s a different course!) It will have been captured by organisms that can make organic molecules—food. We call them producers. Most people think of producers as plants, but they can be Archaea*, Bacteria, or Protists as well. In fact, in some ecosystems the bulk of the work of producing organic food is done by the one-celled residents.

*The domain Archaea includes bacteria-like organisms that live in extreme environments. Biologists once thought they were just another form of bacteria, but we now know their genomes are a bit more like those of plants and animals, and their ways of living very different. You are most likely to find them in salt marshes, hot springs and at the bottom of ocean trenches.

Photo credit: NASA






Content Link: Energy and Planet Earth


Physicists begin the calculation of the amount of energy that a planet could absorb using an ideal case, as if the planet were a “black body.” But of course, Earth isn’t black at all. The relative reflectivity of the surface is called albedo. (Technically, it’s defined as the ratio between the reflected and incoming energies.)


Earth is also more or less spherical, not flat, and its axis tilts at 23.5o away from the plane of rotation. For all of those reasons, the distribution of energy that reaches the surface is unequal.


Electromagnetic radiation exists in a wide range of wavelengths from long radio waves, to cosmic, gamma and x rays.  But 99% of the solar radiation which reaches Earth is found in the region from 0.3 to 3.0 µM, mostly ultraviolet, visible and infrared light.  We often think of visible light as distinct colors with names--red, orange, yellow, green, blue, indigo, violet--but it's really a continuum. At some times of the day the atmosphere skews the colors of light we see, like a "rosy" dawn or a "purple" sunset. And most plants prefer some colors of light to others, even responding to various times of day by opening or closing flowers


The graph at the right shows the relationship of solar energy to latitude. Note that the solar energy is about) the same at the equator in June and December, but at 40o latitude (middle states) there is potentially more solar radiation than at the equator in June. Remember, this graph shows just the theoretical radiation.


Between the equator and 15o N or south (the equatorial belt), it would seem likely that the highest solar radiation would be absorbed. But the cloud cover is a bit higher there. So in the equatorial belt, sunshine is estimated at ~2,500 hours/year. Just north and south of the equatorial belt (15-35o N) there is a lower average cloud cover. There, over 3,000 hours/year of sunshine occurs.


When the radiation reaches Earth’s surface, it is converted to heat, and is transferred by conduction and convection. Often, it’s the atmosphere that transfers the heat. The energy that propels the atmosphere includes heat, but also the energy of Earth’s rotation and gravitation.


You can calculate the solar radiation at your latitude or the latitude of the area where you are taking your “virtual field trip” at http://www.jgsee.kmutt.ac.th/exell/Solar/SolradJS.htm


Photo credit for the Effects of Solar Radiation on Earth’s Atmosphere: USGS http://landsat.usgs.gov/resources/remote_sensing/radiation.php