This mud tells a story. Paleoecology is the textbook.
Sherri's job is to read the story, and to interpret what the diatom and pollen species indicate about the environment.
More on Diatoms.

This micro-Coliseum is actually a diatom called Paralia sulcata. It lives on the bottom of estuaries and marine environments, and disappears if the water gets too fresh or silty.

Achnanthes delicatula is a common brackish water species. It is a good indicator of low salinity and warm temperatures.

Common in oceanic plankton, Actinoptychus senarius likes to catch a ride on other algae.

This is what Ragweed pollen (Ambrosia) looks like. No wonder it makes your nose itch!

This Oak pollen (Quercus) is a little less threatening.

The ratio of Oak to Ragweed pollen changed drastically when Europeans arrived and started clearing land for agriculture. As the trees were replaced by fields, the amount of Oak pollen that fell into the water decreased, and the amount of Ragweed pollen increased. This change is evident when you look at pollen in the sediments. Because we know the time period when land was cleared, we can tell the date when that sediment was deposited. Then we can extrapolate other dates by looking at the density of pollen, and deriving the rate at which the sediments were deposited.