How is the level of carbon dioxide determined from ice core samples?

The correct answer is determined by measuring the CO2 concentration in trapped air bubbles within the ice core samples. Ice cores are composed of layers that have accumulated over thousands of years, capturing air and other environmental data. As snow accumulates and compresses into ice, it traps small bubbles of air from the atmosphere at that time. Scientists extract these cores and analyze the composition of the gas in the bubbles, specifically measuring the concentration of carbon dioxide.

This method provides a historical record of atmospheric CO2 levels, which is crucial for understanding climate change and the Earth's past climate conditions. The trapped air bubbles act as time capsules, allowing researchers to correlate changes in CO2 concentration with historical temperature data and other climatic events.

Other methods, such as analyzing the color of the ice, calculating the density, or determining the thickness of the layers, do not provide direct information about carbon dioxide levels. While these factors can give insight into various conditions of ice formation and the climate at the time, they do not measure gas concentrations directly, making them less relevant for assessing CO2 levels specifically.