how we eavesdrop on ice and mud to hear what the planet's thermostat did before thermometers existed.
means the reconstructed record of earth's past climate, inferred from chemical and physical traces left in natural archives like ice, rock, and shells.
from scientists realized that oxygen isotopes trapped in ancient ice and marine shells shift ratio depending on the temperature when they formed, turning glaciers and seafloor mud into accidental thermometers going back millions of years.
vostok ice core — antarctica, drilled 1998, 420,000 years of climate data
epica dome c — antarctic core reaching 800,000 years, drilled 2004
greenland ice sheet — records abrupt warming events within single decades
foraminifera shells — seafloor fossils tracking ocean temperature over 100 million years