#dennistavery

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helices

7y

Science 0180

When our deciduous trees evolved about 160 million years ago, the CO2 level was about 2,200 ppm - still five times the current level #DennisTAvery

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helices

7y

Science 0178

Our evergreen trees & shrubs evolved about 360 million years ago, with CO2 levels at about 4,000 ppm #DennisTAvery

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helices

7y

Science 0176

Our crop plants evolved about 400 million years ago, when CO2 in the atmosphere was about 5000 parts per million! #DennisTAvery