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Past Climates

Over its long history, our planet has witnessed times when ice extended almost to the equator, as well as 'greenhouse' climates when it was warm enough for cold-blooded reptiles to live north of the present Arctic Circle. Many factors influence global climate such as patterns of ocean circulation, the position of the continents, changes in the Earth's orbit, and the concentration of greenhouse gases in the atmosphere. Studying greenhouse climates from Earth's past helps investigation of the future response of the climate system to man-made global warming.

Evidence for past climates and how they have changed is built up over millions of years in layers of sedimentary rocks and the fossils that they contain. Climatic variables can control both the chemistry of the oceans and how animals take up elements from seawater to make their shells. Some shelly animals alive today are also known in the fossil record. By measuring the chemistry of modern shells from different parts of the ocean, we can quantify relationships between climatic variables and shell chemistry. For example, we know that shells growing in warmer waters have higher magnesium/calcium ratios. Extending this relationship into the past, we can tell the temperature of ancient oceans by the 'proxy' of the Mg/Ca of fossil shells.

The projects below use such methods to study periods of great climatic change.