Which statement best describes what an ice core is?

• A. A sample of ice from a glacier used to study rock formation.
• B. A hollow cylinder used to store ice samples.
• C. A piece of ice formed from seawater.
• D. A cylinder-shaped sample of ice drilled from a glacier used to study past climate.

Answer: (D)

The main idea being tested is what an ice core is and how scientists use it to learn about past climate. An ice core is a cylinder-shaped sample of ice drilled from a glacier. As snow builds up and compresses into ice over many years, each layer traps air, dust, and other clues from that time. By analyzing these layers—including the trapped gases and isotopic ratios—researchers can infer past temperatures and atmospheric conditions, as well as events like volcanic eruptions. That combination of form (a drilled cylinder from a glacier) and purpose (to study past climate) is why this option is the best description. The other statements miss either the actual form, the source (glacier ice vs. seawater or stored samples), or the purpose of analyzing past climate.