Mostly comes from Algae from lake bottoms I believe many years ago.
NOt singling you out. Just wanted to educate some on Carbon.
Carbon is an Element And is on The Periodic table of Elements. Remember that from grade school?
Carbon is not created on Earth or any planet. Carbon is crated at the center of a star. Fusion at stars, similar to our sun, fuse three Helium nuclei into one Helium atom.
So Carbon is only created in a sun or by the death of a sun. If a star is large enough, it will go super nova and spread Carbon and all other elements. Planets form because new sun and solar systems form with these ashes from a dead star.
So, all the Carbon that exists on Earth was here at the beginning of Earth as a hot molten proto planet. Maybe a meteorite with Carbon hits the earth. Only way to add. Launching rockets contain Carbon. Only way remove.
All life on Earth is a Carbon based life form. So any life; plant, animal, fungi, bacteria, algae, etc has Carbon in it. All that eventually dies and puts the Carbon back in the earth. Earth is estimated to be 4.5 billion years old. Plate tectonics crate subduction zones where an entire plate of Earths surface is being pushed under another continental plate. This is how the Carbon gets pushed underground.
We will never run out of fossil fuels. As the price goes up, new technology will be financially feasible to get the oil. Fracking developed thusly.