Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: so many questions on 23/05/2011 11:30:05

Title: Is the total weight of Earth changing?
Post by: so many questions on 23/05/2011 11:30:05

Boyd Foster  asked the Naked Scientists:
   
Hi There Naked Scientists

Is the total weight of planet earth (inc its atmosphere) changing? The variables i can think of are the following.

We burn fossil fuels. Does this increase or decrease the weight?
Population growth (all animals). Is the weight of all species changing the total weight?

Is the only time when we change weight is when a bird fly's? we put a satellite into space? 

Does the weight change as the sun shines through the atmosphere onto the surface?

Does the atmosphere leak into space?

Are we gaining weight from in coming meteorites etc? 

I love your show (http://www.thenakedscientists.com/HTML/podcasts/) and I hope you get a chance to answer my question. I will know if you do or don't as i listen to every podcast (http://www.thenakedscientists.com/HTML/podcasts/).

Boyd from Melbourne Australia.

What do you think?

Title: Is the total weight of Earth changing?
Post by: Phractality on 23/05/2011 21:03:07

You should be asking about mass, not weight. The mass of Earth does increase slightly due to the accumulation of meteors and comets. In the first billion years, a lot of mass was added this way, but the rate has since decreased to a few measely tons per day. The mass occasionally decreases when a very powerful volcanic eruption launches boulders into orbit and beyond. The eruptions of Pinatubo and Mt. StHelens probably sent a few tons of rock beyond Earth orbit. These changes are trivial; even the Chixulub meteor 65 million years ago was tiny compared to Earth. All mass exchanges other than comets, meteors and volcanoes, are many times smaller, still. The total mass has not changed significantly since the formation of the moon and oceans, billions of years ago.

Title: Is the total weight of Earth changing?
Post by: CliffordK on 24/05/2011 09:03:38

The mass of the Earth is generally assumed to include the mass of the atmosphere.  We have burnt several gigatons worth of fossil fuels, enough that there would be a measurable difference in the mass of the crust of the earth, but no difference when you include the mass of the earth & atmosphere together (which is what the sun, moon, and other planets interact with).  This is due to the basic conservation of matter with chemical reactions.

A very slight negative mass change happens in all the nuclear reactors & nuclear weapons.

Not only do meteorites and micrometeorites contain mass, but the solar wind and cosmic ray also contain particles, some of which is absorbed by Earth.  Most of the Carbon-14 on Earth that is used for Carbon Dating is of relatively recent solar origin.  Yet, likely some particles are ejected at the same time the solar wind particles are absorbed with little net change.

The Helium in your party balloons is generally from ancient radioactive decay, and mined along with oil and natural gas.  As the balloons leak or burst, this helium may actually escape Earth's atmosphere.  Notes indicate that in 2008, we mined nearly 30,000 tons of Helium.  Presumably the majority of that was lost into the atmosphere and lost into space.

http://minerals.usgs.gov/ds/2005/140/helium.pdf

If there is actually a mass imbalance, then the loss of fossil fuel Helium might be one contributor to a negative mass balance. 

But, if the Earth weighs
5973600000000000000000000 kg

And we loose
30000000 kg of helium each year.

The loss would still be pretty insignificant.