How do Scientists Know about 1 Million Years of Climate Change? (2024)

Marine Isotope Stages (abbreviated MIS), sometimes referred to as Oxygen Isotope Stages (OIS), are the discovered pieces of a chronological listing of alternating cold and warm periods on our planet, going back to at least 2.6 million years. Developed by successive and collaborative work by pioneer paleoclimatologists Harold Urey, Cesare Emiliani, John Imbrie, Nicholas Shackleton, and a host of others, MIS uses the balance of oxygen isotopes in stacked fossil plankton (foraminifera) deposits on the bottom of the oceans to build an environmental history of our planet. The changing oxygen isotope ratios hold information about the presence of ice sheets, and thus planetary climate changes, on our earth's surface.

How Measuring Marine Isotope Stages Work

Scientists take sediment cores from the bottom of the ocean all over the worldand then measure the ratio of Oxygen 16 to Oxygen 18 in the calcite shells of the foraminifera. Oxygen 16 is preferentially evaporated from the oceans, some of which falls as snow on continents. Times when snow and glacial ice buildup occur therefore see a corresponding enrichment of the oceans in Oxygen 18. Thus the O18/O16 ratiochanges over time, mostly as a function of the volume of glacial ice on the planet.

Supporting evidence for the use of oxygen isotope ratios as proxies of climate change is reflected in the matching record of what scientists believe the reason for the changing amount of glacier ice on our planet. The primary reasons glacial ice varies on our planet was described by Serbian geophysicist and astronomer Milutin Milankovic (or Milankovitch) as the combination of the eccentricity of Earth's orbit around the sun, the tilt of the Earth's axis and the wobble of the planet bringing the northern latitudes nearer to or farther from the sun's orbit, all of which changes the distribution of incoming solar radiation to the planet.

Sorting Out Competing Factors

The problem is, however, that although scientists have been able to identify an extensive record of global ice volume changes through time, the exact amount of sea level rise, or temperature decline, or even ice volume, is not generally available through measurements of isotope balance, because these different factors are interrelated. However, sea level changes cansometimes be identified directly in the geological record: for example, datable cave encrustations which develop at sea levels (see Dorale and colleagues). This type of additional evidence ultimately helps sorts out the competing factors in establishing a more rigorous estimation of past temperature, sea level, or the amount of ice on the planet.

Climate Change on Earth

The following table lists a paleo-chronology of life on earth, including how the major cultural steps fit in, for the past 1 million years. Scholars have taken the MIS/OIS listing well beyond that.

Table of Marine Isotope Stages