Life is a collective phenomenon without a reductionist definition. Chemical biosignatures can suggest the presence of life, but in order to conclusively detect extant life, a relatively long list of life-defining features must be observed: complexity, motion, reproduction, assimilation of nutrients, and metabolism are usually included in the definition. While all of these are to some degree necessary to define a lifeform, not all features are shown by each individual (e.g. reproduction) or measurable on a timescale of a single lifetime (e.g. evolution).
Simple visualization of complex organisms is usually sufficient to show that they are alive. With prokaryotes—bacteria and archaea—the situation is more complex. Cells contain few features to suggest metabolism or complexity, and even electron microscopic levels of resolution cannot necessarily confirm that single microbial cells are alive. Even on Earth, there are significant controversies surrounding “nanobacteria” and the oldest fossils.
Some recent work in the U.S. and elsewhere, particularly Japan, has focused on creating instrument suites containing microscopes for life detection. This lecture will cover some results of this work and ideas for future developments on Earth and in space.
Jay L. Nadeau is a Professor of Physics at Portland State University (2017-present) after 10 years at McGill University in Montreal, Canada, whose research interests include nanoparticles, fluorescence imaging, and development of instrumentation for detection of life elsewhere in the Solar System. Her group was the first to label bacteria with quantum dots, and to explore the possibility of using fluorescent labels as tools for detection of traces of extraterrestrial life. She has published over seventy papers on topics ranging from theoretical condensed matter physics to experimental neurobiology to development of anti-cancer drugs. A believer in bringing biology to the physicists as well as physics to the biologists, she has created seven graduate level courses and written a textbook, Introduction to Molecular Biophysics (Taylor &Francis). She received her PhD in physics from the University of Minnesota in 1996.
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