Earth Science

These images show several different species of diatoms, a type of algae that create houses (called valves) of silica (glass) to enclose their cell contents. As photosynthesizers, diatoms produce 20-25% of the oxygen we breathe.  They are found in all different types of waterbodies at Earth’s surface, including oceans, rivers, and lakes.  Different species have different ecological niches, with some species floating in the water column and others gluing themselves to sediments or plants via a type of mucus they secrete from slits in their valves.  Factors that control which species are found in a particular waterbody include water salinity, temperature, turbidity, nutrient levels (particularly nitrogen and phosphorus), acidity/alkalinity, and flowing versus quiet water, among others.  Because of this, diatoms preserved in lake and ocean sediments can be very helpful in climate reconstructions. 

Foraminifera are marine protists that can be found in environments ranging from the Hudson River Estuary to the deepest reaches of the sea floor. They make hard shells out of calcium carbonate which allows them to be easily preserved in the fossil record. A single teaspoon of marine sediment can contain millions of foraminifera shells, making them ideal microfossils for reconstructing ecosystem structure in the past. Foraminifera shells also record past climate in a different way- their shell chemistry records parameters like ocean temperature, pH, and oxygen. Lastly, foraminifera also contribute to the cycling of carbon and alkalinity in the ocean, making them key players in the climate system. At Vassar, we study living and fossil foraminifera ecology, calcification, and shell geochemistry in order to understand the past, present, and future of our oceans and estuaries.

These images are 1000X magnification of andesite scoria and dacite pumice clasts from Volcán Cosigüina, Nicaragua. We use these images to look at the number, size, and distribution of crystals and vesicles which gives us insight into pre-eruptive magmatic processes (Images 1 and 2). By mapping the distribution of elements using EDS, we can identify the actual phases present in samples. For example, the distribution of magnesium (Mg) in the map shows that we have multiple sizes of pyroxene crystals suggesting there were multiple stages of crystal nucleation before eruption (Figures 3 and 4). Individual crystals have the ability to preserve aspects of their history. The temperature, pressure, and compositional spaces the crystals have been in will affect their chemistry. EDS transects of the crystals can reveal zonation that isn’t easily visually recognizable, even in the BSE image (Image 5, Figure 1)