Carbon dioxide constitutes 0.04% of the earth's atmosphere. At the outset of the industrial revolution in the late 1700s, this figure was about 0.03%. Carbon dioxide is a generally "colorless, odorless, non-toxic, non-combustible gas." It is also (1) the most significant manmade greenhouse gas and "contributes more" to the greenhouse effect than "any other gas" released by human activity, (2) "required for the photosynthesis of all plants," and (3) "vital to life" because "almost all biochemicals found within living creatures derive directly or indirectly from" it.