Earth Mass Increasing? Photons and Photosynthesis making more matter on earth?

D H

... and if that were the case the Earth's surface would rather quickly warm to 5780 K or so.

bhj_dk

trying to sum this up:

through photosynthesis plants convert some of the incoming photons to chemically bound energy (=> mass gain).

plants get eaten by animals, insects, bacteria ect. This converts part of the stored chemical energy to heat which ultimately causes it to be re-radiated (=> mass loss).

But does mass-gain equal mass-loss? or does some of the chemically bound energy (gained mass) get stored?
The amounts of fossil fuels used over the last couple of centuries seems to suggest that some build up of chemically stored energy have taken place.

However; in the very long term the general trend toward entropy suggests an overall loss of mass.

Borek

Frequency doesn't matter here, no idea what you are talking about.

bhj_dk

This is how I understand it: difference in frequency is the same as difference in energy level. And the difference is thought to have been converted to chemically stored energy (= mass).

But argument seems to be based on a "one in/one out" scenario, which - as DaveC426913 writes - is questionable.

SidBala

Inside the sun, fusion takes place. Fusion is a process by which light elements combine to form heavier more tightly bound elements.

So basically:

A + B -> C + energy

But when we add the masses of A and B and then compare it to C, we see that C weighs less than the sum of (A+B). Where did the extra mass go? Well, it turns out that the mass lost is the same as the energy produced in that reaction divided by the square of the speed of light.

The mass lost by the sun is converted into energy that we see as sunlight.

When sunlight is absorbed by the earth, its mass increases by the corresponding factor. However, I have no idea what the scale of this mass increase is. Things like meteors falling into the earth probably far outweigh the increase in mass from this effect.

Photosynthesis - the mass you see as a pumpkin came from the carbon dioxide in the air, water and nutrients in the soil.

In short: yes there is mass lost by the sun and mass is gained by absorbing sunlight. But that is not related to photosynthesis.

Drakkith

Pretty much true, however this energy/mass is also lost as thermal radiation that is radiated away from the Earth constantly. The amount of energy absorbed is equal to the amount radiated away, resulting in no net gain or loss in mass.

Enoki

Bhj_dk has it basically correct. But it does not have to be a plant that absorbers the photon of light. Soil or skin or clouds that capture a photon of light also convert the energy of that photon into mass. The question is how often does that excited electron reradiate the energy versus storing it in a more permanent chemical bond. Both occur. Yes capturing a photon does increase the mass of the earth and yes some of that captured energy/mass does get incorporated into the earths crust.

Bobbywhy

Photosynthesis does not convert sunlight into mass. It converts sunlight into chemical energy (sugars). If one wants to argue the Mass/Energy equivalence, OK, but any increase in the total mass of the earth, if true, would be miniscule compared to the gain in mass from impacts of meteorites and cosmic dust, as several members here have already mentioned.

"The mass of the earth is 5 983 000 zettagrams, and it gains another 40 Gg (gigagrams) every year from captured meteorites and cosmic dust."

http://www.essex1.com/people/speer/large.html

Drakkith

Plus this mass would be lost when the sugar is used in cells, eventually ending up as thermal radiation.

DaleSpam

No, it is re radiated as a larger number of lower frequency photons, so the energy is the same but the entropy is much higher.

davenn

and further to that ... aren't photons supposed to be massless ?
so isnt it irrelevent to discuss their coming to and going from the earth causing an addition or loss of mass of the earth ?

Dave

Drakkith

I don't believe so. Before the photons are emitted the increased temperature of the Earth should result in it being more massive than after the photons are emitted.

D H

No, it's not irrelevant. You have to remember that mass is bound energy. There's two things going on here. Most of those incoming solar photons go into warming things up a bit. A few of those incoming solar photons fuel photosynthesis in plants.

A photon absorbed by a rock makes the rock a bit warmer, and this does make the rock a tiny bit heavier. The same rock is more massive (but only immeasurably) when it is hot compared to when it is cold. Thermal energy is bound energy. There's a problem with this point of view: It's only looking at one tiny part of the picture. Another part of the picture is that the rock cools at night. The rock's temperature exhibits periodic variations, but there is little if any secular drift. The Earth's surface is more or less in thermal equilibrium. This is still but a part of the picture. To look at the whole picture, you need to look at the thermal energy of the Earth as a whole. The Earth as a whole has been and continues to cool down from its very high temperature of 4.56 billion years. In this sense, the Earth isn't gaining mass; it's losing it. Imperceptibly so.

The other route sunlight could be viewed as increasing the mass of the Earth is photosynthesis. The mass of a sugar molecule is larger (imperceptibly so) than the masses of the compounds that went into the making of that sugar. Chemical potential energy is a kind of bound energy. So does this change the Earth's mass? Yes, but this too isn't looking at the whole picture. The plant itself uses most of that bound energy to make starches, cellulose, and other compounds. Animals and fungi eat plants, further reducing the mass gain. A tiny bit isn't recycled by life and will eventually become coal or oil. There is a mass gain here. This still isn't looking at the entire picture. The Earth went through a couple of episodes of "life gone wild!" in which life was very prolific, much more prolific than it is now. We humans have been burning the accumulated bound energy from those episodes at a prolific rate. That imperceptibly small increase in the Earth's mass due to photosynthesis today is more than offset by our consumption of fossil fuels. In this sense, the Earth once again isn't gaining mass; it's losing it. Imperceptibly so.

davenn

thanks for that DH

this isnt my particular field of physics so always willing to learn :)

so, I assume, we aren't even talking about rest mass of a photon, its purely the heating effect caused by the transfer of energy by the absorption of the photon ?

Dave

Drakkith

Exactly.

D H

Correct.

Incorrect. There's also chemistry. Photosynthesis is an endothermic reaction. The sugars created by photosynthesis are more massive than the masses of the compounds that went into forming those sugars; it's a consequence of an endothermic reaction.

DaleSpam

The statement that a photon is massless means that its energy equals its momentum in units where c=1. I.e. The formula for mass in such units is m^2=E^2-p^2. So, if you have an object with m=1 at rest (p=0 and E=1) and it absorbs a photon with E=1 (m=0 and p=1) then by conservation of momentum and energy after the absorption it has E=2 and p=1, which gives m=1.7 So even though a photon is massless another object can still gain mass when it absorbs one.