What will happen to the earth when we begin mining and returning materials from space?

It would keep on spinning.

See: Minerals: large spaces are left behind which usually fill with rainwater/groundwater. Most mines require constant water pumping to keep dry, so once people leave nature takes over. Mines above the water table stay open or sealed as man-made caves until the roof supports decay, and someday they'll collapse. Oil: What happens to the space inside a tire when you let 20% of the air out? Nothing signficant happens at all. The pressure inside that volume goes down, but compressed fluids expand to compensate for the removed fluid. Oil wells stop flowing when the pressure is depleted -- we never vacuum all the oil out from between the rock grains. There is never, ever an empty space. It's really not physically possible. Subsidence can ONLY occur in uncompacted reservoir rocks. In deep reservoirs, the weight of rock above (1 psi per foot depth) crushes and compacts the rock until it adopts a highly compression-resistant lithology. The pressure of the oil/gas/water inside the pores doesn't affect it much, so removing some pressure has no impact. Whereas for SHALLOW rocks, the weight above is not so great and you have weaker, looser uncompacted rock that is partially supported by the fluid pressure inside it -- exactly like a pressurized car tire. When you let the oil flow out, the loose rock grains can no longer support the weight above, and they squish down into denser forms, shrinking the pores between the grains. Likewise letting air out of a car tire makes the car sink toward the ground.

In my experience, water, either from below the formation or, from within the rock itself, replaces the hydrocarbons produced. Many times we are only able to remove 20-30% of the oil &/or gas from the rock formation during primary production because the space occupied by these fluids isn't connected to the other surrounding spaces within the rock and will not flow to the wellbore. Sometimes the formation will allow us to pump water, CO2, etc.down injection wells to help push additional oil & gas to the producing wells but, we are still only able to recover maybe 50% of what is there. We have not seen any impact on the surface or downhole from this extraction process.

It depends upon the mining method. I assume you are referring to underground mining. Many hard rock mining methods leave a relatively stable landform afterwards, but methods like block caving will subside and leave a deep final void. Underground coal mining by longwall methods are designed to subside behing the mining equipment, and the final landform may be lower - approximately 90% of the depth of the extracted coal seam(s) with a 26.5 deg. angle of draw (general assumption used in NSW).

I'm not familiar with the oil side, but as far as minerals go, reclamation varies greatly based on the political jurisdiction.  In the United States, most mines cannot even begin production until a reclamation bond has been floated.  This bond covers all anticipated costs of reclamation for the entire mined out area even if the company goes belly up.  As Rick Muller said, it totally depends on the mining method and what the permit says.  The United States is one of the most difficult countries in the world to start a mining project because of all the permitting and environmental feasibility studies that must be completed.  Open Pit mines usually have to be backfilled with waste rock as much as possible, and then the entire area must be re-contoured as close as possible to its original shape.  Sometimes this isn't completely attainable, and reservoirs are created for recreational use.  As far as vegetation goes, most states require a "hoop throw" vegetation replacement.  Essentially, a biologist or naturalist will throw a series of hoops over the property, and sample the vegetation contained therein.  This mix of vegetation must then be restored in all areas affected by mining. Underground mines have a different reclamation procedure.  I only have experience in Nevada and a few other areas, but typically the mining company must backfill all open areas with mine waste underground.  Hydrologic monitoring wells are drilled to monitor any unlikely contamination to ground water.  Once the mine has been backfilled as much as possible, the mine is capped.  Block caving results in a type of "glory hole" on the surface, but these mines are not very common. Mining has a very negative history associated it; however mining companies today don't survive very long if they treat the environment or their neighbors poorly.  It is always cheaper to completely clean up the site than it is to be a bad mining company and trash the area. I could go into a lot more detail on this if anyone is truly interested.  Most people in the resource development industry want to conserve our natural areas and environment, rather than "rape" it. Some additional reading: http://www.osmre.gov/index.shtm http://www.osmre.gov/topic/awards/Awards.shtm http://www.imcc.isa.us/Photos/Photos.htm http://en.wikipedia.org/wiki/Superfund

Just to be clear, oil production and mineral extraction are quite different cases. Oil and water are held in tiny pores within rock formations (usually sandstone or limestone).  Typically the amount of pore space within deeply buried rocks ranges from nearly 0% up to perhaps 15%.  If the pore space in rocks is connected (referred to as "permeability"), then fluids can circulate through the rocks.  The vast majority of subsurface fluid is water, with oil only occurring under certain conditions.  An oil reservoir usually occurs in a subsurface rock structure where a permeable reservoir rock is covered by an impermeable rock layer, trapping an accumulation of fluids underneath.  Just as on the surface, oil floats on water, so an oil well will tap the layer of oil in the upper part.   As the oil is removed it is usually replaced by water from below.   (In rare instances - usually very shallow wells - the reservoir rock may not be fully compacted or consolidated, so eventually removing fluid & lowering pressure will cause the overlying ground to settle.  This is unusual, however.)  In summary, the overall impact on the planet is pretty small.  "Oceans" of oil might be overstating the case... perhaps "lakes" is more to scale. Most minerals & metals, on the other hand, are tightly bound to the rocks they occur in.  Extracting them is mostly a brute-force exercise in digging up the rock and grinding it up.  Depending on the nature of the mineral, that means either underground mines or large open-pit excavations.    In the worst cases these may end up as eyesores and sources of groundwater pollution.  But as noted elsewhere, they can also be refilled & reclaimed, or turned into lakes.  While it may seem that mankind's impacts on Earth are dramatic, I find it helpful to remember that the planetary time scale is millions-to-billions of years.  In a few million years, virtually all evidence of current human activities will have been eroded away.

Chuquicamata Chile  over 4 km wide and almost 1 km deep Russia   note proximity to town Peru  next to populated area The differences in environmental regulation in the US and abroad is starkly shown by open pit mines next to populated areas. In the US coal mines have to be returned to their former state at the expense of the mining company. If a former gold mine in South Africa looks better it is only because rain turned it into a lake. It does not rain in the desert areas of Chile and the copper in Chuquicamata is endless. The story of the largest open pit mine, Chuquicamata, reads like a melodrama of predatory capitalism. It was owned by Anaconda, which had a bad reputation in both Montana and Chile. At one time or another Anaconda was owned by the Rockefellers, the Rothchilds and the father of William Randolph Heast. It was nationalized in 1971 by the Socialists. When the CIA and Pinochet got rid of the Socialists the Constitution was re-written by the military to give 10% of the income from copper to themselves. Predatory unregulated mining companies are not only create scars in the earth but in the lives of  entire societies.

Mass of the earth = 5.972x10^24 kg 1 Trillion = 1x10^12 Lets say we bring back 100 trillion kg of materials New Earth Mass = 5.9720000001x10^24 Gravity is g=G*Me/Re^2 So old gravity is        6.67300x10^-11(5.972x10^24)/(6371x10^3)^2        = 9.81806072145m/s^2 And the new gravity is        6.67300x10^-11(5.9720000001x10^24)/(6371x10^3)^2        = 9.81806072161m/s^2 This seems like quite a negligible difference so I would not expect much to change because of it.

Water is pumped down old oil wells to flush out the last of the oil, the water is left behind. Opencast  mines are often allowed to flood to form lakes which are then used for fishing, boating and yacht clubs etc or used as waste dumps. In remote areas worked out opencast mines are quite often just left. Deep mines are usually just capped and left.