Summary:
- The article discusses the Phanerozoic eon, which spans the last 541 million years of Earth's history, and the reconstruction of atmospheric CO2 levels during this time period.
- It highlights the use of various proxies, such as the stomatal density of plant fossils and the isotopic composition of marine carbonates, to estimate past CO2 concentrations.
- The article suggests that the Phanerozoic eon has experienced significant fluctuations in atmospheric CO2 levels, which have had a profound impact on the evolution of life on Earth.