Supply of energy is not infinite. Longevity of energy is.
I sent your question to a friend of mine who is a hard rock geologist who scouts for mines. - here is his answer - Let me know what you think.
He’s got reserve and resource backward. Also, there are no categorized resources in space or “the deep core of earth”. The second last question makes my head hurt, and seems like a non-sequitur. The last one makes me wonder what he means by “limited or decrease”.
The price of commodities will incorporate the energy cost to get it out of the ground in the long run. That’s supply and demand. The definition of ‘reserve’ is that which can me mined at a profit. Resources are defined as extensions of reserves which might be mined, based on statistically less certain drill data. Resources can be brought into the reserve category or condemned with further drilling. If energy prices make mining unprofitable, mines will close. Then commodity prices will rise to cover the shortage and many of them will become economic again.
I get old. I mixed up resources and reserves.
What your friend tells you is pretty much what I have learned on university. If you spend half an oil field in energy and a billion Dollar on equipment, no matter what it is, you will probably get it out of the ground, so supply in this sense is not limited.
But this relation holds not true for mining energy itself. If you spend more energy than you extract afterwards, than by definition you are running a monetary loss, as well (energy as a factor of production and hence price). But whether you regard the monetary balance or the energy balance, energy in this case becomes limited - in either sense you can’t extract it economically.