Dating sediment cores


Anyone with a messy desk understands one of the cornerstones of earth sciences: newer stuff collects on top of older stuff.It’s this fact that allows us to reconstruct the past using ice and sediment cores drilled from ice sheets and from the sea floor.The enormous ice sheets that cover Greenland and Antarctica are up to several miles thick.They contain layer upon layer of snow that fell, never melted, and compacted into glacial ice.Within this ice are clues to past climate known as For example, gas bubbles trapped in the ice contain chemical clues that reveal past temperature.The same bubbles tell us the concentration of atmospheric gases—including important greenhouse gases such as carbon dioxide and methane.



Most of this sediment is made up of the miniscule shells of microscopic sea life.Since particular microbes live only under particular environmental conditions, scientists can use them to track changes in water temperature and chemistry over millions of years.As with ice cores, ash, dust, and pollen found among the layers can tell of other environmental events and conditions taking place around the globe at that time.An apparently strong argument for an old earth is the seeming agreement between multiple (and supposedly independent) dating methods which yield “millions of years.” Uniformitarian scientists claim that chemical clues within the seafloor sediments tell a “story” of climate change over millions of years and that this “story” agrees well with expectations of the astronomical (or Milankovitch) theory of Pleistocene ice ages.

Yet secular scientists routinely use the astronomical theory to date the seafloor sediments in a technique called “orbital tuning.” Of course, this argument is circular, since the astronomical theory of ice ages is simply assumed to be correct and is used as a framework for interpreting chemical clues within the seafloor sediments.

Secular scientists have recognized the circularity in this argument and have attempted to guard against it by using “independent” checks on the orbital tuning method.