

Earth Mass Gain and Gravitational Field Intensity
Name: Robert
Status: other
Grade: other
Location: CA
Country: USA
Date: Winter 20122013
Question:
The earth gains approximately 40,000 tons a year in mass through dust and meteor strikes. That is 2,600,000,000,000 tons since the KT event. What effect on earths gravity would that have?
Replies:
It would have a negligible effect. That mass is around 12 orders of magnitude less than the mass of the earth.
Tim Mooney
Hi Robert,
Thanks for the question. Remember that the mass of the Earth is on the order of 10^24 kg. The number of tons you quote below is a small fraction of this mass, so we should expect little effect from this added mass. However, adding mass to the Earth does two things: it increases the gravitational force that objects experience and it increases the radius of Earth. These effects are seen by Newton's Law of Gravitation.
I hope this helps. Please let me know if you have any additional questions.
Thanks
Jeff Grell
Good question, but considering all the things that have gone on since then such as erosion of mountains, continents drifting, mountains being created and so on, I would be willing to say any effect of that mass has been overpowered by all the other changes.
I do not think we can separate the effect of the mass from everything else that has gone on. Earth is a really big place if the addition of that much mass can be lost "in the noise", isn't it?
Hope that helps.
Robert Avakian
Robert,
Negligible. You need to compare the added mass to the total mass of the earth which is about 6x10^24 kg (6 followed by 24 zeros). I use this notation, called scientific notation, since it is easier to deal with such large numbers. Using your value for the added mass, the earth has added about 3x10^9 kg. If we divide this number by the total mass, we get 5x10(14). In other words, the earth has added 0.000000000005 % of its total mass since the KT event. This total increase would have negligible (essentially zero) effect on Earth's gravity.
Kyle Bunch, PhD, PE
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Update: November 2011

