The researchers used the fossilized remains of ancient plant tissues to produce a new record of atmospheric CO2 that spans 23 million years of uninterrupted Earth history. They have shown elsewhere that as plants grow, the relative amount of the two stable isotopes of carbon, carbon-12 and carbon-13 changes in response to the amount of CO2 in the atmosphere. This research, published this week in Geology, is a next-level study measuring the relative amount of these carbon isotopes in fossil plant materials and calculating the CO2 concentration of the atmosphere under which the ancient plants grew. because major evolutionary changes over the past 23 million years were not accompanied by large changes in CO2, perhaps ecosystems and temperature might be more sensitive to smaller changes in CO2 than previously thought.
— source Geological Society of America | Jun 1, 2020