Final answer:
When carbon dioxide levels were lower due to decreased atmospheric presence, the energy absorbed by Earth's surface decreased, leading to a cooler climate and, in extreme cases, ice ages.
Step-by-step explanation:
When climate researchers in Greenland discovered an ice core sample that displayed a period of decreased carbon dioxide in the atmosphere, the amount of energy absorbed by Earth's surface during this time likely decreased. Carbon dioxide is a greenhouse gas that contributes to the greenhouse effect, a natural process that warms the Earth's surface. When the levels of carbon dioxide are lower, this effect becomes less intense, allowing less heat to be trapped and causing the overall temperature of the planet to cool down. As such, past periods with low carbon dioxide levels have even been linked to ice ages, times when the planet's surface was extensively covered by ice and snow.