What is crude oils function within the ecosystem of the planet?

Crude oil is the product of chemical reduction of carbon based life forms that have died and have been buried under ground. (reduction is the reverse of oxidation) The reduction causes the formation of hydrocarbons. To generalize hydrocarbons are chemicals that are in a cl called lipids (or fats, inedible fats in the case of crude oil but fat none the less). Also over time hydrocarbons can form into more complex molecules called paraffin(wax). They move out of their source rock and get washed along underground by ground water through the pore spaces in rocks. Since oil floats on water the hydrocarbons float up into traps where a curious creature on this planet can drill it out of the ground and use it for a wide variety of uses. Otherwise over millions of years it will slowly seep up to the Earth's surface and dissipate into the ecosystem. There are also subterranean bacterias that can make a meal of oil but are not sufficiently present to eat it all up. If you want to get rid of carbon dioxide from the atmosphere the best way is to get the oceans to eat it. I wouldn't worry about running out of hydrocarbons any time soon. There is pleanty of source rock full of oxygen deprived carbon based rocks still producing new hydrocarbons. Be sure when your oil well stops producing oil to plug the formations up tight with cement they will slowly start to refill again. Finally I would like to say that there are no big holes in the ground full of oil. An oil reservoir is just pore spaces in rocks that are filled with oil and natural gas. As the oil is pumped out ground water fills in right behind it. Drilling oil out of the ground has no effect on the temperature in the Earth's core. Heat is transported from the core by convection in the Earth's mantle. The heat comes up places where it meets the least resistance, mainly the mid-ocean ridges, and volcanos. Every time a volcano goes boom heat is let out from the inside. Please remember that the temperatures inside the core are hot enough to melt rock into liquid and thats how the heat gets out. One of the main sources of heat in the Earth's core is the decay of radioactive potium isotopes, this is also true in the mantle and crust. One of its left overs is a stable atom of Argon. Argon is nearly 1% of the Earth's atmosphere by volume.