Chapter one can be found here.
Where Carbon Comes From
Water and element number six in the form of Carbon Dioxide are the two largest gaseous products of volcanic activity. Having floated around the universe for a while, element six was part of the cosmic dust that coalesced into our solar system and planet. Still mysterious internal churnings spew molten rock and these gasses continuously on our planet today. The current annual volcanic production of CO2 is thought to be only about a third of a gigaton, so it is considered insignificant in the annual Carbon cycle. Oxygen is two doors down at number eight in our cosmology and there are two of them in CO2. The atomic numbers are proportional to the weight so total annual volcanic Carbon is a measly tenth of a gigaton. We will be talking about gigatons a lot. It is easy to become cavalier about moving hundreds of them around. A gigaton is the weight (on earth) or mass of a cubic kilometer of water.
This is a USGS photo of a volcano in Alaska. If we take the tenth of a gigaton for an average year and extend it back three billion years to when things had settled down enough for the earth to have a crust and some sort of oceans with stromatolites in it, we get three hundred million gigatons of Carbon that should be found in various reservoirs. The totals for the reservoirs in a typical Carbon Cycle imodel are only about sixty thousand gigatons, so you can see we have a lot of missing Carbon. More serious estimates put the total Carbon stored in the earth’s crust at as carbonate and fossil fuels as high as one hundred million gigatons. This is still short by two thirds.
Stromatolites like these in Australia were producing Oxygen from CO2 three billion years ago. The real question seems not to be where did the Carbon come from, but where did the Carbon go?
Some carbonate is subducted back into the crust at ocean trenches. There is reason to believe that volcanic activity may have been higher in the dinosaur era but we really don’t have much to go by before that because the ocean floor has been recycled. It is possible we live in a volcanically active time that does not accurately represent the last three billion years.
We will chalk the missing Carbon up to just another unsolved mystery. It seems more than just coincidence that volcanoes produce the elements essential to life. Carbon and Oxygen alone comprise eighty three percent of human body weight and that lightweight Hydrogen another ten percent. For all this you can thank volcanoes. You can also thank them for the water in the oceans.