12 September, 1997

One of our daily rituals is a group meeting after lunch. This is a time when Fiona reviews the mission's progress and individual teams report any findings or concerns that have developed over the past 24 hours. The last half-hour is designated for "science tidbits", a general overview of one of the scientist's work or interests. I always look forward to these lessons. Today, Paul and Gary, environmental chemists who study contaminants in the sediments, described how they plan to determine the age of the core samples they are collecting.

Their dating techniques make use of two events that left a time stamp on our planet, the ban on atmospheric nuclear testing in 1963 and the melt down of the reactor core at the Chernobyl nuclear power plant in 1986. These events altered the amount of a radioactive isotope of cesium in our atmosphere. The concentration peaked in 1963 when testing stopped and has been decreasing since because the isotope decays with a half-life of 30 years. When their samples are returned to the lab, they will cut it into 5mm thick sections. The concentration of Cs-137, along with a number of other elements and compounds, will be measured in each section. When they find the section with the highest value, they can date the layer as 1963. By a similar technique, using a naturally occurring radioactive isotope, Pb-210, they will determine the rate that sediments are accumulating. With this information they will not only be able to detect the presence of contaminants but will also know when they were first introduced into this environment and the rate they are increasing or decreasing.

Another core sample