When studying the issues concerning Mars colonization, one thing that struck me was the problem of hydrocarbons, e.g. lubricants and plastics. On Earth, we get mineral oil based lubricants and plastics almost for "free". They come from petroleum, natural gas and coal tar. The cost on Earth for these products is poking a hole in ground, shipping the raw material to a refinery and then shipping the finished product to the consumer. On Mars, carbon dioxide from the atmosphere and water ice stripped mined from the ground need to be chemically recombined using an energy source into a hydrocarbon (methane or cellulose). The methane/cellulose then needs to be polymerized into lubricants and plastics. This is all very expensive. Here's a quick quiz: Which is more valuable to a Martian? A machine made drinking cup of pure gold or a hand made foot stool of ordinary pine? Answer: Wood products and human labor are much more valuable on Mars.

Gary