I learned in a physics class that energy cannot be either created or destroyed. It just changes form. Almost all energy on earth comes or came from the sun. The exceptions would be nuclear and geothermal. My question concerns geothermal energy. I am assuming (perhaps incorrectly) that the earths molten core gets its heat from gravitational compression of the planet. If this is true it seems that if there was a practical way to tap into this geothermal energy it would be a never ending source of energy as long as you didn’t use it at a faster rate than it is replenished. This leads to my real question; where is the replenishment coming from? Are there waves of “gravitational energy” flowing through the universe? Perhaps my assumption that the energy is being replenished is wrong and the core heat is just residual from the formation of the planet and not from gravitational compression at all.
A certain amount of the heat is coming from friction due to the innards of the earth being pulled back and forth by the graviational pull from the Moon. Also, just because there’s a whole lot of something doesn’t mean it’s infinite. There is more than enough geothermal heat to satisfy energy needs pretty much forever if a way is found to harness it safely and effectively.
I thought it was conjectured that a large portion of the heat which we currently have in the Earth is a result of nuclear decay products?
You wouldn’t be getting an endless supply of energy by tapping geothermal sources. You’d just get a seemingly endless supply of energy.
The earth is hot from impacts of meteors and the like (in the early formation of the earth) and more now by radioactive decay and compression. Right now the earth is cooling off and has been cooling for about 3-4 billion years or so.
In that time we have managed to form a crust several miles thick in some places but that still leaves several thousands of miles of molten mantle and solid (but very hot) core underneath us.
If we started tapping geothermal energy for our use we would accelerate the process of cooling. Given the tremendous amount of energy present in the earth’s mantle and core it would take eons for man’s energy consumption to put much of a noticeable dent in it much less exhaust it. You are not getting a perpetually renewing source of energy however. Keep at it long enough and eventually you’d cool the earth into a solid ball of rock.
Unfortunately tapping geothermal energy is easier said than done and so far hasn’t proven very cost effective. Still you never know…maybe someday.
Check here: http://renewable.greenhouse.gov.au/technologies/geo/geothermal.html for a good source of info on geothermal energy.
Small scale extraction of geothermal energy in localized and concentrated areas is practical where hot springs, driven by lower volcanic action, reach the surface. New Zealand and Iceland are good examples, but it is used in lots of other countries.
As the web site explains, you could regard geothermal energy as a renewable resource and ‘energy forever’, but the current extraction is not, as involves extracting a localised resource at a greater rate than it is created. These sites are effectively being mined.
Unfortunately the means to extract geothermal energy in any other way is currently beyond us.
I recently went on a tour of a geothermal power plant (my power company gets 50% of its power from geothermal sources). Their pamphlet had an URL of a slideshow which may answer your question. It’s 122 screens, so you’ll have to check for yourself:
http://geothermal.marin.org/GEOpresentation/sld001.htm