How do scientists determine how much CO2 was in the atmosphere thousands of years ago, and to what level of certainty are they able to perform these calculations?

Question

How do scientists determine how much CO2 was in the atmosphere thousands of years ago, and to what level of certainty are they able to perform these calculations?

In: Earth Science

Answer 1

One method is to analyze ice. They drill deep holes in very thick glaciers. So the ice from down below is very old, even thousand of years and hast small bubbles of gas included. This gas is very old air which can then be analyzed.
Almost a million years ago, the ratio of heavy and light isotopes of oxygen (O 16/ O 18, H / D or hydrogen to deuterium) provides us with information about temperature. It is crucial that in the process of evaporation of the ocean water, i.e. the phase transition from liquid to gaseous, the isotopes of the constituents of the molecule water (H2O), i.e. O 18 or D compared to the “normal” atoms O 16 or H, depending on the the temperature of the ocean water changes into the gaseous phase at different speeds. Isotope physicists speak of temperature-dependent defraction