please consider this botanical information:



C4 plants have a competitive advantage over plants possessing the more common C3 carbon fixation pathway under conditions of drought, high temperatures, and nitrogen or CO2 limitation.

C4 carbon fixation has evolved on up to 61 independent occasions in 19 different families of plants, making it a prime example of convergent evolution. This convergence may have been facilitated by the fact that many potential evolutionary pathways to a C4 phenotype exist, many of which involve initial evolutionary steps not directly related to photosynthesis. C4 plants arose around 35 million years ago during the Oligocene (precisely when is difficult to determine) and did not become ecologically significant until around 6 to 7 million years ago, in the Miocene.

[link to en.wikipedia.org (secure)]



C4 plants (such as grass) grow faster than C3 plants (such as tomatoes) in conditions of low carbon dioxide.

C4 plants evolved about 35 million years ago and started growing real fast about 6 or 7 million years ago.

This shows that the planet has had low carbon dioxide conditions, with C3 plants starving for carbon dioxide, for about 30 million years.

In the last 6 or 7 million years the carbon dioxide levels have got so low that the C4 plants are now consuming about a quarter of the terrestrial carbon dioxide. This is despite there being about 20 times as many C3 plants as C4 plants. The C3 plants can't compete at these low levels.


"Today, C4 plants represent about 5% of Earth's plant biomass and 3% of its known plant species. Despite this scarcity, they account for about 23% of terrestrial carbon fixation."