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If scientists want to know what Earth's climate was like in the past, they study  Rellenar huecos (1): JXUwMDJiJXUwMDE2JXUwMDAxJXUwMDBkJXUwMDA0JXUwMDA4JXUwMDBiJXUwMDFh  cores  and  ice Rellenar huecos (2): JXUwMDNiJXUwMDBjJXUwMDFkJXUwMDE3JXUwMDE2 . Rellenar huecos (3): JXUwMDBiJXUwMDM2JXUwMDAxJXUwMDBkJXUwMDA0JXUwMDA4JXUwMDBiJXUwMDFh cores come from the bottoms of lakes or the ocean floor. Rellenar huecos (4): JXUwMDExJXUwMDJhJXUwMDA2 cores are drilled from deep — sometimes miles — below the surface of the ice in places like Antarctica.

A drilled Rellenar huecos (5): JXUwMDMxJXUwMDBhJXUwMDA2 core kind of looks like what you get if you plunge a drinking straw into a slushy drink and pull it out with your finger over the end of the straw.