Structural Function

Wood exists for a reason.

When plant life started to boom on the early earth, light became the most sought-after commodity. To get more light meant to become taller than the surrounding plants. The only way to become tall is to build structural support. A few million years of this constant struggle and voila, wood.

Sixty percent of the mass in all living organisms at any given time is the wood from some 3,000,000,000,000 (trillion) trees. In terms of carbon, that is 300 gigatons.