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Although this image could be mistaken for a catastrophic planetary event, it is actually a living microorganism, a foraminifer—about the size of a grain of sand. Ironically, fossilized foraminifera in limestone deposits around the planet have provided evidence that an asteroid struck the Earth some 66 million years ago. Foraminifera are one of the most-used archives of past ocean chemistry. It is from the foraminifera that scientists first understood that ice ages occurred periodically with a regular timing over the last million or so years. They also provide a window into how the planet responded to an acidified and hot ocean, the Paleocene-Eocene Thermal Maximum (PETM), which occurred around 56 million years ago, when the climate was warm, and an ocean acidification event killed off many marine taxa—the most recent event in the history of the earth that is comparable with current global warming.
Celebrate Asteroid Day on Friday, 30th June, 2017.
Living foraminifera are plucked out of the water by hand, and placed one-by-one into glass jars while diving. In fact, a trained diver can distinguish foraminifera from the rest of the plankton using the glint of the sun off their spines, and identify and select foraminifera by species while in the water. This living foraminifer was photographed in the laboratory using dark field light microscopy. The little granules on the spines are dinoflagellate photo symbionts. The foraminifera are about 500µm–1mm across.
Alex Gagnon, PhD, School of Oceanography, University of Washington, Seattle and Howard Spero, PhD, University of California at Davis.