Quaternary Era

Proxy Data

Using the changing oxygen isotope ratios from ice cores and marine sediment cores, scientists have discovered global changes, recorded synchronously over a wide range of latitudes. One long climate proxy record was taken in the Antarctic, the Vostok core. From it, the inferred temperature over a long interval is based on the temperature-sensitive ratio of oxygen isotopes, 18O to 16O. In the Vostok core, isotopes of oxygen have been used to develop Earth temperature histories extending over 400,000 years. Trapped gas bubbles record the history of atmospheric CO2 concentrations for over this period (data from the National Climatic Data Center, Asheville, North Carolina). Because the isotope 18O is heavier than 16O, the proportions of each vary depending on the climate region. In alpine areas such as in the Alps of Switzerland and in the polar regions, 18O is more abundant, while in the lowlands of the middle and low latitudes 16O prevails in the atmosphere. By calibrating these, scientists can use the proportions of oxygen isotopes taken from ancient sediments or ice cores as an index of average annual temperature.

The changing proportions of isotopes can be matched and dated with a geomagnetic signal of polar reversals (the Earth's poles changed in magnetic signals), a known time scale based on isotopically dated magnetic signals that are worldwide. Another source of long climate records are the deep-sea sediment cores from which oxygen isotopes can be extracted from calcareous plankton (foraminifera). These data carry the paleoclimatic records back through more than 60 million years through the Tertiary period and the time of the last dinosaurs.

The Ice Ages, which comprised the main part the last million years, was a globally cold period with increasingly variable swings of climate. The glacial pattern continued over long intervals, with only a few comparatively short warm or interglacial periods. The last major glaciation came in two parts; in the United States, these are called the early Wisconsin (80,000–28,000 years before present, oxygen isotope stage 4) and the Full Glacial or late Wisconsin (23,000–15,000 years ago, oxygen isotope stage 2); between these a somewhat warmer middle Wisconsin period occurred 28,000–23,000 years ago. The maximum of the last major glaciation occurred about 18,000–15,000 years ago (called the Full Glacial). After 15,000 years ago, a global warming began, and continental ice sheets melted by about 10,000 years ago. The period after 10,000 years ago, or postglacial, is called the Holocene or Recent period representing the present interglacial.

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