There is much more geologic evidence for the younger geologic ages, such as the Quaternary period, which spans the last 2 million years of the Earth's history. During the Quaternary, global climate has alternated between times of warmth and frigidity—interglacial and glacial episodes. The Quaternary is separated into two epochs, the Pleistocene (10,000 years to 2 million years ago) and the Holocene (10,000 years to the present).
The Pleistocene is best known for its glacial and interglacial intervals. Geologists have been able to find an abundance of evidence with which to reconstruct the geologic past during this time frame. Through the analysis of deep-sea sediment cores and windblown loess deposits on land, geologists have been able to determine when, where, and how long glaciers advanced across the Earth's surface. Loess is silt that has been deposited by wind action. It usually forms near the borders of continental glaciers and is the material eroded by glacial meltwater and then transported by wind.
One of the more helpful techniques used to study past climate change is analysis of oxygen isotopes. By studying fluctuations in oxy-gen-18 (18O), it is possible to calculate past ocean temperature and global ice volume. The 18O ratios are studied in ice cores obtained by scientists in places such as Greenland and Antarctica. The 18O trapped in the ice gives climatologists a clear indication of what climate was like when it was deposited. Many scientists believe the glacial cycles during this period were driven by influences from the Milankovitch cycles— changes in the Earth's tilt, eccentricity, and precession.
Variations in atmospheric CO2 are considered another major factor in determining the climate during the Pleistocene. Climatologists agree that a strong correlation exists between temperature and CO2 levels, that is, that the greenhouse effect has played a significant role in the Earth's global climate, especially over the past 160,000 years. A redistribution of carbon took place among the various carbon reservoirs on Earth—the atmosphere, ocean, land, and biosphere—but the exact relationship that triggered the glacial and interglacial intervals is not clearly understood. Three notable events occurred during this time period: (1) the Penultimate Interglacial period, (2) the Dansgaard-Oeschger events, and (3) the Heinrich events.
Was this article helpful?