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Is Mother Earth getting fatter ?

  1. Sep 7, 2004 #1
    Is Mother Earth getting "fatter"?

    I was wondering if during the process of photosynthesis if energy from the sun is actually converted into matter, such as sugers and plant material. I found in a reference book that stated that plants use the energy from the sun for growth but it didn't state at that point that plants actually convert energy from the sun into matter. Later on the article states that plants absorbed energy (light) from the sun.

    I once read that 8 pounds of sunlight hits the Earth every second. What do you say? Is the Earth getting fatter in this respect?
  2. jcsd
  3. Sep 7, 2004 #2
    No. The light energy is not being converted into matter. The light is used in the process of photosynthesis to break bonds, the plants are using matter that is already on earth and are making products that remain on earth. The products of plants are used by other organisms, and ultimately everything returns back to the plants.

    It's a cycle. The most basic way to think of it is plants take in CO2, and make O2. People take in O2 and make CO2. There is a lot more to it than that, but the matter stays in a cycle.
  4. Sep 7, 2004 #3
    are photons considered to be a matter?
  5. Sep 7, 2004 #4
    Are photons particles or waves


    From the newly-created Physics Forums glossary:

    • photon The photon (from Greek, photos, meaning light) is a quantum of excitation of the electromagnetic field and is one of the elementary particles studied by quantum electrodynamics (QED).

      In layman's terms, photons are the particles that make up electromagnetic radiation, although, according to quantum mechanics, all particles, including the photon, also have some of the properties of a wave.

    Interestingly, Wikipedia had earlier posted an identically-worded definition.
  6. Sep 7, 2004 #5
    Yes, the earth does get heavier as a result of photosynthesis

    Your answer violates one or more laws of conservation of mass-energy. The correct answer is, "Yes. The process of photosynthesis converts energy from the sun into matter. The matter is incorporated into chemical-energy-storage items such as sugars and plant material, though not discretely. The added material is in the form of additional mass."

    Photons have mass. Eight pounds of photons drop on the earth every second. This photonic mass does not magically disappear. Some of it radiates away, but whatever is stored as potential chemical (petrochemicals) or potential kinetic (water in a hydropower reservoir) adds mass to the earth.

    Yes. And energy is stored as potential energy when these bonds are broken. Creation of potential energy always results in proportional creation of matter. Lift a pencil from a floor to a desk and mass has been added to the pencil. Knock that pencil off the desk and the same amount of mass converts into energy. Shine sunlight on plant material so that it grows and eventually decays into butane and mass – exactly proportional to the addional potential chemical energy – has been added to the material. Flick a lighter filled with that butane and the chemically stored mass-energy is released, making the earth then a little lighter and a little hotter since mass was converted into energy.

    The energy in coal is put there ultimately from sunlight. Is the earth's coal carrying the weight of ancient photons? Yes. The photonic mass never went anywhere. Any photons that have been captured by the earth and turned into potential chemical energy have contributed to the mass of the earth. How much mass? For every year that a typically-sized gigawatt-electrical coal power plant runs, almost one kilogram of matter is turned into energy.

    In converting back into energy, the mass has literally vanished from the universe. But it isn't magic. It is simply an aspect of the laws of conservation of mass-energy.

    Normally we associate conversion of mass into energy with nuclear processes. For example, running a typically-sized gigawatt-electrical nuclear power plant for a year also converts about a kilogram of mass into energy (the nuke plant converts a little more per equivalent amounts of electricity produced since nuke plants are not as thermally efficient as coal plants and the amount of mass converted into energy depends directly upon how much thermal energy is produced). However, storage of energy in the form of mass, and re-conversion of that mass back into energy, generalized broadly – to pencils, to butane, to coal, and to nukes.

    To reiterate for the original poster: Yes, the earth does get heavier as a result of photosynthesis.
  7. Sep 8, 2004 #6
    To: hitssquad

    I disagree. Photons do not have mass. The sentence I said about "8 pounds of sunlight strikes the Earth every second" was not to be taken literally. That conclusion of "8 pounds" was brought about by using Einstein's famous field equation of e=mc^2. Using this equation one can find the potential amount of mass of a certain amount of energy has.

    I know that the earth is gaining mass from dust and other particle material that falls to the earth from the solar system.
  8. Sep 8, 2004 #7
    Accounting for the 8 pounds of mass-energy

    Thanks for the correction. Per Wikipedia, for a particle to have invariant mass it needs both energy and momentum, and a photon only has energy. Regardless, the earth gains weight when photosynthesis occurs, and the weight gain is both equal to 1. the potential chemical energy newly stored in the plant during any given period of photosynthesis; and 2. the energy of the photons absorbed that is not accounted for by heating of the plant or any other energizing of the plant by the photons.

    The 8 pounds of mass-energy still has to be accounted for. It is either (immediately or after a short while in the form of radiated heat) radiated away into space or absorbed as potential energy (at least, but not necessarily limited to, potential kinetic and potential chemical energy).
  9. Sep 8, 2004 #8
    It is mainly semantics, but I (and more importantly many respectable physicists) consider light not to be classified as matter.

    Bosons, such as light, are forces mediators. You can fill a box with as many photons as you want (until the box blows up for energetical reasons)

    Fermions do not like each other. You can fill a box with fermions until no more can be added. Fermions are considered as matter.
  10. Sep 8, 2004 #9
    Notice also that, if you fill a box with photons, and nothing goes out to the outside the box gets more and more heavy.
    Last edited: Sep 8, 2004
  11. Sep 8, 2004 #10
    This is way more relevant.
  12. Sep 8, 2004 #11


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    ... and while we're at it ... it loses billions of tonnes (every year?) of hydrogen through photodissociation of water at the top of the atmosphere (also some helium).
  13. Mar 2, 2005 #12
    It might be irrelevant. but I got a Question to ask…What would happen if plants are put in different PH of water? If plants are denaturated where would the energy then go? Back to mother earth?
  14. Mar 2, 2005 #13


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    ...and the Earth gains over 100 tons every day from impacting micrometeors
  15. Mar 2, 2005 #14


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    The Earth is an equilibrium system as far as energy is concerned -- it gains energy from sunlight, and loses roughly the same amount of energy via infrared radiation, etc. If it weren't in equilibrium, its temperature (or accumulation of chemical energy stores) would be rising constantly, or falling constantly, global warming excepted.

    That said, the Earth is not getting more massive due to photosynthesis -- the light that falls on plants is eventually converted to heat (perhaps by an animal down the food chain a bit), which then escapes the Earth as infrared radiation. The exact same thing happens with light that hits bare ground, but the process has fewer steps.

    I should also note that whether or not light has "mass" is an irrelevant question, loaded with all kinds of complicated nuances. It is much easier to consider that in general relativity, the theory which describes gravity, both matter and radiation are treated simultaneously in the same way. In other words, both matter and radiation are affected by gravity, and affect other objects gravitationally. As far as gravity is concerned, matter and radiation are the same stuff, and it doesn't really matter what other labels you want to apply to them.

    - Warren
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