Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: thedoc on 04/08/2015 02:50:01
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Ken Devey asked the Naked Scientists:
I have always wondered about the amount of crude oil that has been extracted from the earth and the weight that has been taken from the earth. I know water enters the oil cavity but it does not replace the weight that has been taken out of our planet. Would this weight reduction effect the position of the earth at all?
What do you think?
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Extracting oil from the crust for use on the surface (or in the atmosphere) has no effect on the mass of the Earth! The mass just moves from one part of the Earth to another part, and therefore has negligible effects on the gravitational interaction between the Earth and the Sun.
Only when we launch rockets into space (beyond Earth orbit) is there any reduction of mass in the Earth, and this is also essentially negligible (all objects we have launched beyond the orbit of the Earth almost certainly add up to less than 1000000 kg, which would only be less than 0.00000000000000001% of the mass of the Earth)
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It seems we have move something like 135 billion tonnes of oil from the bottom of the wells to the top and then set fire to it.
But the earth weighs something like a thousand billion billion tones. (5.972 × 10^21 t from Google).
And, of course most of it only moved a few miles up (then spread round a bit)
To compensate the ground above the well will have fallen slightly too.
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Actually, there is a slight decrease in the Earth's mass.
Einstein's famous equation Ε = mc² describes the relationship between mass and energy. The mass of a single atom might be very small, but the c in that equation is the speed of light squared, or 300,000 kilometers per second times 300,000 kilometers per second. So, the number you're talking about is the mass of the atom times 90 billion.
To put this into perspective, think about what a particle accelerator does, which is basically working the opposite way. In that case, you take two protons, for instance, total mass of those protons combined is very low, but then they accelerate them to speeds approaching 300,000 kilometers per second and collide them. Even then, they can barely "create" "heavy" particles with mass out of protons colliding at high speed despite the tremendous amount of kinetic energy added by two protons moving at that speed.
At any rate, whenever energy is "created" by some sort of process to fuel some sort of process or activity, there is a loss in mass, but since the speed of light squared is such a huge number, the actual mass lost is negligible. It's sort of like burning a log. If you could gather together all the ashes, evaporated water, soot particles that floated away, etc, and collect them back together, you would nearly equal the mass you had previously, but some of it would have escaped and dissipated as photons, energy that was helping to hold all that stuff together as mass, energy that was originally incorporated into those molecules when the tree built it out of soil and water using photons.
At any rate, without doing any math, just guesstimating, I would say you could probably burn a trillion tons of coal and that would only amount to a few grams of lost mass, or something like that, not enough to throw off most chemists' observations of processes involving trillions of molecules.
Of course, one might argue that photons are massless, but that's only when they are travelling through space as "free energy." When they are bound to a system, as they are in energy-containing molecules used for fuel, they do indeed contribute to mass.
All this stuff is generally known as Mass-Energy Equivalence, other related specific concepts would be Binding Energy, Combustion, and Photosynthesis.
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Actually, there is a slight decrease in the Earth's mass.
Einstein's famous equation Ε = mc² describes the relationship between mass and energy. The mass of a single atom might be very small, but the c in that equation is the speed of light squared, or 300,000 kilometers per second times 300,000 kilometers per second. So, the number you're talking about is the mass of the atom times 90 billion.
I presume, Craig, that you are assuming that all the thermal energy leaves the Earth system thus changing the planet's mass? If the heat from burning the oil remains behind, would that not contribute to increased mass of the hotter particles?
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I know water enters the oil cavity but it does not replace the weight that has been taken out of our planet.
Water is denser than oil, so the weight of the solid crust has increased.
When the oil is burned, it returns to the surface as water (directly) and carbon dioxide (sequestered by plants), so to a first approximation, there is no net loss of mass, just a redistribution.
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I presume, Craig, that you are assuming that all the thermal energy leaves the Earth system thus changing the planet's mass? If the heat from burning the oil remains behind, would that not contribute to increased mass of the hotter particles?
It's not like me to assume anything. Of course, some of the energy leaves the earth...
https://en.wikipedia.org/wiki/File:NPP_Ceres_Longwave_Radiation.ogv
... while some of it is trapped by the atmosphere, which makes the Earth habitable in the first place.
https://www.koshland-science-museum.org/sites/default/files/GreenhouseEffect.jpg
The Greenhouse Effect is a good thing. Climate Change is too much of a good thing.
Here's something related to your second question:
https://en.wikipedia.org/wiki/Binding_energy#Mass-energy_relation
Sorry, not sure why those didn't post as links. I'm pretty new here.