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mroulston@yahoo.com
2008-Feb-22, 08:54 AM
Just thinking about Mass and energy. When Crops and trees etc grow does the mass of the earth increase, When these resorces get used what is the result ? What Im really thinking about, does the process of life produce Mass directly from energy, (Sunlight) We are more familiar with converting Mass to Energy, burning fossil fuels and so on. Is Life the most efficent way of producing Mass from Energy? What other process can you think of that do what life does?

Ken G
2008-Feb-22, 09:24 AM
Every time the Earth stores heat from the Sun, its mass increases-- but by an extremely tiny amount. Life does not necessarily cause the permanent storage of heat-- plants do store that energy, but animals that eat plants release that energy. Any overall planet in equilibrium would have it "come out in the wash" when you also factor in death, decomposition, etc. However, on a planet that is growing huge forests where there were none, I think you can say that a tiny tiny mass increase does occur, not because of the mass of the trees, but because of the tiny amounts of chemical energy stored in those trees that was not stored previously.

JohnD
2008-Feb-22, 09:30 AM
mr,
You confuse mass to energy with the energy involved in synthesising molecules and breaking them down again.

Mass to energy only occurs when an atom's nucleus decays, with the release of several particles and nuclear fragments, or with the fusion of nuclei with a bit of energy left over.

Crops and trees grow by taking existing atoms and sythesize them into new molecules, using sun energy to bond them with new interatomic bonds that leave the nuclei unchanged. When those bonds are broken, by digesting food or burning wood, the stored energy is released. The Law of Conservation of Mass states that in chemical reactions the mas of the compounds involved is constant, and this was an important developemt in our understanding of chemistry. The concept lead to the the Law of conservation of energy, the First Law of Thermodynamics. Ultimately, it might be said to lead to Einstein and e=mc^2, which says that energy AND mass are conserved, and cannot be created or destroyed, but may be converted into one another.
See:http://dbhs.wvusd.k12.ca.us/webdocs/Thermochem/Law-Cons-Mass-Energy.html

John

Delvo
2008-Feb-22, 01:40 PM
Ken G's talking about the way movement increases an object's or particle's mass as it gets closer to the speed of light, or the fact that the interchangibility of matter and energy means that an energy increase could be described as a mass increase. When something gets warmer, the particles it's made of move more, and more movement means more mass in that sense. (Particles' masses are normally given as constants, but that refers to "rest mass", which doesn't include the "relativistic mass" that it gains with movement.) But the effect is so tiny that it's practically zero because things generally move at much closer to zero speed than to light speed, and it's not specific to plants but applies to anything that gets warm in sunlight, and it doesn't explain what plants really do with sunlight or where a plant's mass really comes from. So the answer is off-topic and unnecessarily confusing for the inquirer, but accurate.

The real way to answer the given question is to describe what plants do with sunlight and where the mass of a plant's body comes from. It has nothing to do with matter/energy conversion or the change in mass that occurs with speed; it's chemistry, not relativity. When compounds in the plants called "pigments" (a word biologists use for substances whose role or job to an organism has to do with absorbing and reflecting light) absorb the sunlight, those molecules end up at a higher energy level than before, meaning that the molecule's constituent particles are in an "excited" state and interacting with each other a bit differently from the way they were before. It's chemical energy now instead of radiation, and chemical energy can be passed from one molecule to another, drive some chemical reactions or be shed by other chemical reactions in the form of new radiation, and change the structure of molecules. What the plants do with that energy is the same thing that non-photosynthesizing organisms like us do with the chemical energy in the food we consume: use it to move atoms and molecules around and rearrange them in the forms we want... metabolism/digestion, catabolism, immune system activity, physical movement, growth, mitosis, reproduction, excretion, healing injuries, filtering out or destroying toxins, controlling internal fluid pressure and pH...

So, because what plants do with sunlight is just move atoms around, that means that every atom of a plant's body was somewhere else before the plant collected them. And how it got them is different for different elements. By far the vast majority of any organism's mass is composed of four elements: carbon, hydrogen, oxygen, and nitrogen (sometimes abbreviated together as the pseudo-word "CHON"). A plant gets carbon and oxygen from the gases of the air. It also gets hydrogen from the air indirectly, from water in the form of rain which soaks into the soil and is absorbed by the roots. It gets nitrogen from the air even less directly than that: some kinds of bacteria which live in soil can take in atmospheric nitrogen gas, then excrete simple nitrogen radicals like nitrite or nitrate (I don't think it's both but I forget which), which are soluble in water, which means a plant can absorb those radicals by its roots as it absorbs water from the soil.

So, most of any organism's mass is converted air. The small fraction that's left over aside from those consists of a lot of different random other elements like sodium, iron, potassium, and copper. These are also soluble in water, and can be found in tiny amounts in almost any soil, dissolved in the thin layers of water that adhere to the surfaces of soil particles. When plants absorb the water, they absorb these other dissolved elements, and the rest of us get them when we eat plants or eat something else that ate plants.

Ken G
2008-Feb-22, 01:41 PM
Mass to energy only occurs when an atom's nucleus decays, with the release of several particles and nuclear fragments, or with the fusion of nuclei with a bit of energy left over.No, the only difference between nuclear energy and chemical energy is that nuclear energy is generally almost a million times more, per particle. Still, anything that stores energy, nuclear or chemical in nature, increases mass. However, you are right that this is almost never included in chemical energy equations because the effect is so very tiny, and it might not be what the OP is addressing.

Hornblower
2008-Feb-22, 01:44 PM
mr,
You confuse mass to energy with the energy involved in synthesising molecules and breaking them down again.

Mass to energy only occurs when an atom's nucleus decays, with the release of several particles and nuclear fragments, or with the fusion of nuclei with a bit of energy left over.

Crops and trees grow by taking existing atoms and sythesize them into new molecules, using sun energy to bond them with new interatomic bonds that leave the nuclei unchanged. When those bonds are broken, by digesting food or burning wood, the stored energy is released. The Law of Conservation of Mass states that in chemical reactions the mas of the compounds involved is constant, and this was an important developemt in our understanding of chemistry. The concept lead to the the Law of conservation of energy, the First Law of Thermodynamics. Ultimately, it might be said to lead to Einstein and e=mc^2, which says that energy AND mass are conserved, and cannot be created or destroyed, but may be converted into one another.
See:http://dbhs.wvusd.k12.ca.us/webdocs/Thermochem/Law-Cons-Mass-Energy.html

JohnI disagree. As I understand the meaning of the famous equation E = mc2, any absorption or release of energy is reflected reflected as a respective gain or loss of mass in the involved object. In theory it is not restricted to nuclear reactions. It just happens to be too slight in ordinary chemical reactions to be detected with any laboratory balance. Sure, we could in principle create a theory in which it applies only to nuclear reactions, but I prefer to invoke Occam's Razor and take Einstein's work as correct.

mugaliens
2008-Feb-22, 02:15 PM
Yes, some sunlight is stored in the growth of plant matter (photosynthesis). It's miniscule, however, compared to the energy given off by the Earth.

JohnD
2008-Feb-23, 10:11 AM
Yes, some sunlight is stored in the growth of plant matter (photosynthesis). It's miniscule, however, compared to the energy given off by the Earth.

Mugs
"the energy given off by the Earth"
Please, please explain!
Have you hit on the answer to all our energy problems?

Horns,
Does that mean that when I stretch a rubber band, its mass is increased?
You invoke Occam's razor, but energy is not converted into anything but energy when it is stored as potential energy, in a (relatively) motionless spring, or a chemical bond. Why use Relativity, when ordinary mechanics can explain, especially when the alternative involves changes in mass 'too small to measure'.
John

Hornblower
2008-Feb-23, 03:14 PM
Mugs
"the energy given off by the Earth"
Please, please explain!
Have you hit on the answer to all our energy problems?The Earth is very hot inside, and that heat is gradually leaking out through the surface. In theory, we could install heat exchangers deep underground and tap into this heat to meet our energy needs. In present day practice, this is more expensive than using fossil fuels. When those fuels eventually run out, we might find the geothermal approach to be profitable.


Horns,
Does that mean that when I stretch a rubber band, its mass is increased?If Einstein and his successors are right, the answer is yes, by a very tiny amount. For such a small amount of energy there is not a balance on the face of the Earth that can detect it.

You invoke Occam's razor, but energy is not converted into anything but energy when it is stored as potential energy, in a (relatively) motionless spring, or a chemical bond. Why use Relativity, when ordinary mechanics can explain, especially when the alternative involves changes in mass 'too small to measure'.
JohnThat is a very good question, and the act of answering it is a good educational experience for both of us. My reasoning is as follows:

In "ordinary mechanics" as understood before the 20th century, we developed a concept of potential energy to interpret the observed behavior of a rubber band as it was stretched by measurable forces. This was consistent with the general theory of energy as firmed up by Newton and others. In the general theory energy is an attribute of the system which can be transformed from one variety to another while ultimately being concerved. These varieties include kinetic energy, gravitational potential, elastic potential (in the stretched rubber band), to name a few. In no cases at the time was there a measurable change in mass when energy was gained or lost, and there was no motive for considering a hypothetical change.

In the 20th century we were aware of reactions in which extremely large gains or losses of energy are accompanied by measurable mass changes. At the same time improved instruments were showing that the measured speed of light was independent of the observer's motion. These phenomena, along with some unsolved electromagnetic mysteries, led Einstein to develop his comprehensive theory in which matter and energy are equivalent, rather than being separate attributes.

If we accept the idea that Einstein's theory applies to all varieties of energy, including the rubber band stretch potential, it will predict that the rubber band is more massive in its stretched state. Since the amount is too small to be measured on any device we have been able to make, there is no conflict with the results of our experiments in "ordinary mechanics". Thus we invoke Occam's Razor and do not bother trying to create a different theory for this variety of energy.

In a thought experiment we could create a balance capable of measuring the change in mass, and in doing so we could test the theory for these small amounts of energy. If we were to find no mass change for this example, we would know that Einstein's theory is oversimplified and that more research is needed to explain this type of energy. If we do find the change predicted by Einstein, we uphold his work and conclude that our superduper instruments have refuted the previous "ordinary mechanics" theory.

JohnD
2008-Feb-23, 06:20 PM
Thank you, Horns, for such a measured (!) answer.
I am educated.
Would the OP's question, about the gain in Earth's mass from growing crops,trees etc. be a measurable quantity with your imaginary scales? Of course as Ken said, this will probably be balanced across the globe by the complementary growing cycles at different latitudes through the year.

But I'm still not convinced by geothermal energy. Sure, we could and probably will have to, tap into that but how much escapes every year, compare with the amount of solar energy available? Maybe Mugs should answer, but how does the "energy from the earth" compare with the energy fixed by plants?

John

Ken G
2008-Feb-23, 06:54 PM
If we accept the idea that Einstein's theory applies to all varieties of energy, including the rubber band stretch potential, it will predict that the rubber band is more massive in its stretched state. Since the amount is too small to be measured on any device we have been able to make, there is no conflict with the results of our experiments in "ordinary mechanics". Thus we invoke Occam's Razor and do not bother trying to create a different theory for this variety of energy.You're right that we don't know if rubber-band potential energy works that way (or at least neither of us have heard of such an experiment), and that we will expect it does until we have a reason to think otherwise. One form of potential energy that we do have experiments on is gravitational potential energy, which is kind of self-referential when dealing with gravity itself so I don't claim it's the same as a rubber band. But the gravitational potential energy of a neutron star has a very noticeable effect on reducing the mass of the neutron star (by perhaps 20% or so IIRC). Were that not the case, neutron stars might be impossible-- their own self-gravity might always crush them into black holes, and we shouldn't have pulsars.

Hornblower
2008-Feb-23, 08:04 PM
Thank you, Horns, for such a measured (!) answer.
I am educated.
Would the OP's question, about the gain in Earth's mass from growing crops,trees etc. be a measurable quantity with your imaginary scales? Of course as Ken said, this will probably be balanced across the globe by the complementary growing cycles at different latitudes through the year.That depends on how sensitive we make our thought-experiment balance. Typical chemical reactions have a predicted mass change on the order of 1 part in 10 billion. If we could build a balance capable of detecting 1 part per trillion and used it to weigh the reactants before and after photosynthesis, we could detect it.


But I'm still not convinced by geothermal energy. Sure, we could and probably will have to, tap into that but how much escapes every year, compare with the amount of solar energy available? Maybe Mugs should answer, but how does the "energy from the earth" compare with the energy fixed by plants?

John
See the thread about "Earth's intrinsic power" for reference.

A quick check with Wiki revealed about 15 terawatts for the worldwide human consumption of energy. If we were to get it by drawing down on the residual heat inside the planet, it would take billions of years to exhaust it. I estimated that from the known mass, rough estimates of heat capacity, and an internal temperature of several thousand degrees K.

The best estimates we have found in the midst of discussion on that thread indicate about 44 terawatts of leakage from the interior at the present time. Yet the core is still blazing hot after over 4 billion years. It simply is hard to grasp the vast amount of heat inside a planet.

JohnD
2008-Feb-24, 10:40 AM
I found a figure for the intensity of sunshine at Earth surface of 1 Kilowatt/m^2 (http://www.eppleylab.com/Intro.htm) Translating that into the solar radiation total for comparision with geothermal demands that the incidence of the sun onto the globe, duration of day at different latitudes is considered. So approximate by considering a flat surface the diameter of the Earth.

At 12736 kilometers diameter that's 127.4x10^6 k^2. (the coincidence of the digits is just that!)
Or 127.4x10^12 m^2
At 1kw/m^2 that's 127.4x10^15watts.
Or 127.4x10^3terawatts.
Compare with your figure of 44 terawatts of leakage from the core.
Ken? The sun provides three times as much radiation as the Earth's internal heat.
Please check my arithmentic - there are a lot of orders of magnitude there and a gross approximation!

As the climate is so dependent on the Sun's rays, and on how they are captured by surface and atmosphere, I'm still sceptical about how much that leakage contributes to plant growith, and the sums back me up.

John

Hornblower
2008-Feb-24, 01:08 PM
I found a figure for the intensity of sunshine at Earth surface of 1 Kilowatt/m^2 (http://www.eppleylab.com/Intro.htm) Translating that into the solar radiation total for comparision with geothermal demands that the incidence of the sun onto the globe, duration of day at different latitudes is considered. So approximate by considering a flat surface the diameter of the Earth.

At 12736 kilometers diameter that's 127.4x10^6 k^2. (the coincidence of the digits is just that!)
Or 127.4x10^12 m^2
At 1kw/m^2 that's 127.4x10^15watts.
Or 127.4x10^3terawatts.
Compare with your figure of 44 terawatts of leakage from the core.
Ken? The sun provides three times as much radiation as the Earth's internal heat.
Please check my arithmentic - there are a lot of orders of magnitude there and a gross approximation!

As the climate is so dependent on the Sun's rays, and on how they are captured by surface and atmosphere, I'm still sceptical about how much that leakage contributes to plant growith, and the sums back me up.

JohnYes indeed, the amount of solar energy absorbed by the surface and atmosphere vastly exceeds the amount that comes from the interior.

I never argued that the internal heat had much if any effect on plant growth, and I don't see any such discussion anywhere in this thread. This is a big digression from the OP topic concerning mass/energy equivalence.

Argos
2008-Feb-24, 01:44 PM
When Crops and trees etc grow does the mass of the earth increase,

I think there´s no need to complicate the answer ot this question. The mass contained in plants, animals, in the form of chemical elements was already present elsewhere on the planet. It is only transformed, something addressed by Antoine Lavoisier in the 18th century.

Ken G
2008-Feb-24, 02:02 PM
The sun provides three times as much radiation as the Earth's internal heat.
Please check my arithmentic - there are a lot of orders of magnitude there and a gross approximation!I think you mean three thousand times. So we basically have three heat fluxes to think about-- 127,000 terawatts directly from the Sun (at the cloud tops), a similar flux from the Earth that was absorbed from the Sun (we can't use it twice, but some things like wind power essentially draw from that second-chance pool), and 44 terawatts welling up from the core. Humans, on the other hand, use 14. So to use solar energy for all our needs, we'd need about 0.1% efficiency (pretty hard to imagine such a high efficiency over such a huge planet), and to use geothermal energy for all our needs, we'd need more like 30% efficiency (a completely impossible ideal). It would seem that solar, wind, and hydroelectric power will never be able to supply our growing energy needs, and geothermal will be a fairly negligible blip.

I realize it's a digression, but 14 terawatts works out to be about 2 kilowatts per human. So it is as though we all have 20 bright light bulbs on all the time (I realize we on here use ten times that share). The geothermal heat is like 60 bright light bulbs per human, and sunlight is like 200,000. That sounds like a lot, but the sunlight that actually hits our body is only about one bright bulb. Note this also means each person could live alone in a land area about 10,000 square m. That's an average distance of roughly 100 meters between people on land. Interesting numbers, it's a pretty crowded planet after all.

JohnD
2008-Feb-24, 09:34 PM
Thank you, Ken, three thousand it is!

Argos, please read the whole thread above - it gave me something to think about, even if only about mass changes too small to measure! If Ken and Horns are right then added energy will ADD to the original mass of the elements that originally made up the Earth, and like Newton, Lavousier was only right until Einstein.

John

George
2008-Feb-24, 09:51 PM
I realize it's a digression, but 14 terawatts works out to be about 2 kilowatts per human. So it is as though we all have 20 bright light bulbs on all the time (I realize we on here use ten times that share). The geothermal heat is like 60 bright light bulbs per human, and sunlight is like 200,000. That sounds like a lot, but the sunlight that actually hits our body is only about one bright bulb. Note this also means each person could live alone in a land area about 10,000 square m. That's an average distance of roughly 100 meters between people on land. Interesting numbers, it's a pretty crowded planet after all.
Using solar energy, 2kw doesn't seem all that difficult to acquire. One half of a roof, the sunny half, might be around 65 m2 for an average house. At 10% efficency, only about 12 m2 is needed assuming an average of 340w/m2, the average solar energy across the planet, falls on the collector over a 10 hour period.

Of course, trees could be a problem. If your neighbor has trees that block your collectors, just make him cut them down, even if they are Redwoods (http://www.mercurynews.com/ci_8063034). :doh: It is worth mentioning that the daily household a/c need drops dramatically given a house shaded by trees.

[BTW, were you thinking of the cross sectional area of the Earth (127 million sq. km.)? The Sun gives us 174 terawatts above the clouds, at least per Wiki. This changes almost nothing of what you've said, however.]

Argos
2008-Feb-24, 10:17 PM
Argos, please read the whole thread above

My mistake. I thought the question was simpler. Hasty reading. Gotta be more careful in the future.


Lavousier was only right until Einstein.

Needless to say ;)

Ken G
2008-Feb-24, 11:25 PM
2[/sup] is needed assuming an average of 340w/m2, the average solar energy across the planet, falls on the collector over a 10 hour period. But a family of 4 needs 4 times as much on average...

[BTW, were you thinking of the cross sectional area of the Earth (127 million sq. km.)? The Sun gives us 174 terawatts above the clouds, at least per Wiki. This changes almost nothing of what you've said, however.]

Gosh I hope that's not true-- if humans use 14 and the Sun only sends us 174 total, we'd need almost 8% efficiency over the whole planet, so more like 30% on land. Did you mean 174,000 terawatts? At least that only requires 0.03%, which sounds a bit more reassuring.

George
2008-Feb-25, 03:52 AM
But a family of 4 needs 4 times as much on average... A very good point. :) Perhaps 48 sq. meters of roof is needed of the 65 available. Probably all 65 sq. meters, or whatever is the more accurate figure, could be utilized, which might eliminate the shingle costs by replacing them with collectors, somehow. The surplus wattage could go into the grid to serve the clouded areas.


Gosh I hope that's not true-- if humans use 14 and the Sun only sends us 174 total, we'd need almost 8% efficiency over the whole planet, so more like 30% on land. Did you mean 174,000 terawatts? At least that only requires 0.03%, which sounds a bit more reassuring. With your help, I think we now have it... 174,000 terawatts. :)

mroulston@yahoo.com
2008-Feb-29, 01:09 PM
Some great answers Gentlemen, Thanks for your thoughts on my question. If indeed there is a small increase in the earths mass, Is there any other process that can do what life does in this regard

Ken G
2008-Feb-29, 01:57 PM
Sure-- anything that stores energy does it. Take Venus-- it has a whopping greenhouse effect. Compared to a period prior to the onset of that greenhouse warming, Venus would now have a higher mass as a result of the greater heat. But the difference is so puny, compared to the mass of the planet itself, that I hesitate to even mention it-- you just seemed to be asking for the perfectly literal mass-energy equivalency.