Sediments in marshy water are instructive, she explains, because
they contain pollen, seeds, diatom skeletons, and other traces
of their time. These reveal the plant and animal life, and thus
the climate. The sediments "just lay down very slowly and
quietly," forming layers almost as clear as tree rings. So
today, looking at sediments from places like Dan's Bog,
Maryland, Brush can understand the climatic and ecological
shifts of the past 12,000 years. The sediments speak especially
clearly for the last 350 years, because since the original
forest was put to the plough, much more sediment has run off
into the water. By the late 1800s, Maryland was only 20 percent
forested. Brush says "you can correlate the amount of organic
carbon directly with human development in the drainage area."
Once, it took the mother of all hurricanes to lay down a
centimeter of sediment, more than 1,500 years to lay down 10
centimeters. Today, a centimeter may deposit in one routine
year. Brush says the most fundamental change has t