On Tuesday, August 2, 2005, at 08:09  PM, Keith Thomas wrote:
> CO2 with modern equivalents. He found that today's plants had the
> lowest levels of calcium,
> copper, iron, potassium, magnesium, sodium, sulphur, and zinc than at
> any time in the last three
> centuries."

This may just be a fertilization effect. CO2 is a plant nutrient. When
the level is high, plants grow faster and so other nutrient levels are
lower. Same thing is true if you use lots of N. Anything that speeds
plant growth will have this effect.

Co2 levels have risen and fallen quite a bit over the course of time.
Currently they are in the lower end of the range. Plants are adapted to
much higher levels than current.