In the early 1600s, Johann Baptista Van Helmont grew a willow tree under very controlled conditions. He filled a pot with 200 pounds of kiln dried earth, planted a willow sprig, watered it with rainwater, and after five years, weighed the tree.
To quote Van Helmont: "... the tree sprung from thenc, did weight169 pounds, and about 3 ounces.... I computed not the weight of the leaves that feel off in the four Atumnes."
Further, he wrote: "At length, I again dried the earth of the vessel and there were found the same 200 pounds, wanting about two ounces."
To Van Helmont, the conclusion was obvious: "therefore, 164 pounds of wood, bark, and root arose out of water only."
Since two ounces of earth could not possibly have transmuted to 169 pounds of tree, the tree must be made from the rainwater that he had used to carefully water the growing tree over the years. As water was the only other ingredient present, what other explanation could there be?
Actually, he wasn't really that far off. Water from the soil and from the air is a chief component in the growth of all plant life. But more important is carbon dioxide. The photochemical reaction in which 6 water molecules and 6 carbon dioxide molecules are combined to give a glucose molecule and 6 oxygen molecules is the basis of life on Earth.
It perhaps was surprising to Van Helmont that soil is not really necessary for the growth of plant. Of course, many people now know this - just ask anyone who has grown plants or vegetables using hydroponics.
Indeed, this is why trees can be seen on mountain sides growing in the most inhospitable places such as tiny cracks in the face of a cliff. Tufts of grass and other vegetation can also been found in places with little or no soil.
All that is really required is carbon dioxide, water, and a small amount of minerals (the two ounces of soil in Van Helmont's experiment). It is the mineral content that does tie plants to earth and must be added to the water in hydroponics.
This very old experiment has some modern implications, though, for modern climate change mitigation strategies. In particular, there is considerable discussion in the international community about "carbon dioxide credits". (The provincial government is heavily vested in carbon credits.)
The idea is that where a country has growing forests that are soaking up carbon dioxide from the atmosphere, there is a sense that this should offset the cost of some of the total amount of carbon dioxide being produced through the combustion of fossil fuels by that country.
Indeed, there is an argument that with increasing carbon dioxide levels, the enhanced growth of the forests should make these "carbon dioxide credits" more significant.
Unfortunately, science doesn't agree. Many controlled experiments in which forests or agricultural stands have been exposed to artificially high levels of carbon dioxide have found that forests are not the insatiable sinks for carbon dioxide that global change studies often assume.
After an initial surge, the growth rate of the vegetation living in a region with an artificially enriched carbon dioxide atmosphere slowed down unless the plants are provided with additional minerals in the form of fertilizers. Multi-year studies do not find that plants are capable of soaking up the excess carbon dioxide emissions.
Further, experiments have demonstrated that while the amount of leaf litter on the forest floor increases, so did the rate of decay. This means that the carbon dioxide is not getting trapped in the leaves and needles to be eventually interred in the mineral layers of the soil but returning to the atmosphere.
The result is that while forests may act as "carbon dioxide credits", removing some of the carbon dioxide from the atmosphere, they are not going to respond to increasing carbon dioxide levels by gobbling up the excess and burying it in the ground.
The balance between the atmosphere and the biotic systems has been established over millions of years. It is an equilibrium predicated on predictable chemical processes.
By adding carbon that was interred millions of years ago and therefore removed from the carbon cycle back into this equilibrium, the whole system will shift to find a new equilibrium. That shift will have an impact on our climate. And as we keep adding more carbon to the atmosphere, a new equilibrium is not going to be established any time soon.
Vegetation may require carbon dioxide and water to grow but it is that couple of ounces of dirt that provide the nutrients. And without more nutrients, the plant life wherever it is found on Earth is not going to save us from increasing carbon dioxide levels.
