I would like to know what percentage of the Earth's crust is made up of organic material (dead plants & animals, aka soil)?
Also, if you happen to know… what is the rate at which organic material on the Earth expands or grows deeper?
Interesting question. There are several types of organic matter in the Earth's crust: soil/sediment organics and fossil organics (coal, oil) at deeper levels. I suppose the total percentage of organic material in the crust should be small, but here's an attempt to put some numbers behind that:
A high average organic content for soil is 5%, and the soil layer is just a couple meters deep. Let's assume that the ocean sediment layer is similar in organic content and somewhat deeper than soil layers. Therefore, let's assume the depth of the soil/sediment layer is averages 10 meters. This yields an average 50 cm depth of organic matter in the soil/sediment layer.
Coal is the primary component of fossil organics. An area rich in coal would have multiple seams, with each seam being tens of meters thick, so let's assume a total depth of 100 meters. Perhaps 1% of Earth's surface contains such rich coal deposits, so spread over the entire Earth's surface, this would yield an average coal depth of 1 meter. *
The depth of the Earth's crust varies from about 5km on the ocean floor to about 40km over land, and there's roughly 3x more ocean area than land, so let's say the global average depth of crust is 15km.
Using the assumptions above, all of which purposefully lean towards the upside, a first order approximation of the organic content of the Earth's crust would be: (.5 m soil + 1.0 m fossil organics) / (15,000m) = 0.0001
So, as an upper limit, perhaps about 0.01% of the Earth's crust would be organic material.
….
Another answer here looks at the question from a geological perspective, and includes limestone as organic because it is derived from organic material, which is true. But from a chemical perspective, limestone (CaCO3) is usually considered to be inorganic, because it doesn't contain a carbon-hydrogen (C-H) bond. And from a biology perspective, even coal would be considered inorganic, because it isn't biologically active. Unfortunately, the distinction between organic and inorganic is, in some cases, a matter of definition….
http://chemed.chem.purdue.edu/genchem/topicreview/bp/1organic/organic.html
…. and so the answer to your question would also depend on which definition of "organic" is most relevant to your problem.