Earth processes play out at different rates--a hurricane grows in strength in a few days whereas it takes many millennia to grow an ice sheet. Understanding the rate of change in different parts of the Earth system naturally requires having accurate geological clocks that tell us when and how long events happened in the past. In 'deep time', millions of years ago, we have been successful in identifying a regular cycle in Earth history produced by changes in Earth's orbit around the sun.  This 'orbital chronometer' has been calibrated to 'tell time' back to about 40 million years.  Unfortunately, the astronomers cannot uniquely determine Earth's orbital chronology before this, resulting a series of alternative time scales for Earth events. So while there is one "Earth clock" for the past 40 million years, we have a number of alternative clocks for time before 40 million years ago, only one of which is telling 'true time'.  Which clock should we pay attention to in the deep past?

Our project was designed to link the well known astronomical clock for the past 40 million years with one of the 'floating' chronologies for times older than this.  We did this by reconstructing the most highly resolved record yet of the orbital climate cycle to provide a unique 'clock' of Earth history. We used a marine sediment record from the North Atlantic which we believe has a continuous record of environmental change in the deep sea.  We extracted microfossils from the sediment and analyzed their chemistry, which gave us a detailed record of environmental change.  In turn, we compared that record to the various orbital clocks to see which ones match best.

Last Modified: 10/08/2016
Modified by: Richard D Norris