Increasing mass of Earth

Main Question or Discussion Point

Since each day we are illuminated by the sun, plants convert that energy into glucose etc does this indicate an increase in mass of the earth if losses due to heat radiating out and gains such as meteors are ignored?

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mgb_phys
Homework Helper
Plants don't convert sunlight into food by E=mc^2
They just use the energy of sunlight to cause a chemical reaction (making sugar from CO2+water) when they eat the sugar it goes back to CO2 and H2O - rther like a rechargeble battery/

The Earth's mass does increase mainly from dust and ice that falls from space plus a lot of charged particles form the sun

Xnn
Plants don't convert sunlight into food by E=mc^2

Sorry, Einstein didn't make an exception for plants!
However, plants store energy by converting sunlight into chemical bonds.

So, the real question is if CH2O and O2 weigh more than CO2 and H2O.

Will have to check this out later...

Astronuc
Staff Emeritus
So, the real question is if CH2O and O2 weigh more than CO2 and H2O.

Will have to check this out later...
The cellulose and plant structure should weigh less than the constituent CO2 and H2O, but the difference is going to be very small, probably in the ppb range since the bond energies are on the order of eV, not MeV or GeV.

Light enables plants to restructure CO2 and H2O into more complex molecules, but the number of nucleons and electrons doesn't change, and that is what mgb_phys was indicating. Matter is not created, it is only transformed. But one is right, the sunlight energy becomes stored chemical energy.

On the other hand, the earth does capture some of the solar wind, so it does gain mass that way, and there is the odd meterorite that strikes the earth.

Earth's heat balance is pretty stringently balanced. A tiny, tiny fraction of the incident energy might be stored as chemical bonds and a certain amount of carbon is buried each year, thus leading to a net rise in oxygen levels - i.e. it's stuff that can potentially burn, but hasn't.

Meteors and interplanetary dust particles add about 40,000 tons of mass to Earth each year, but it loses a couple of kilograms of gas per second, thus there's actually a net decrease of about 20,000 tons per year.

The cellulose and plant structure should weigh less than the constituent CO2 and H2O, but the difference is going to be very small, probably in the ppb range since the bond energies are on the order of eV, not MeV or GeV.
The photosynthesis (Calvin) cycle is

6CO2 + 6H2O + ~ 48 photons <-----> C6H12O6 + 6O2

The heat of oxidation of this reaction is about 29 eV. The total mass of the sugar + oxygen is ~272 AMU = ~346 MeV. The energy difference is about 84 ppb. Where is the 29 eV (heat of oxidation) stored? Is the chemical (potential energy) stored as a mass difference?