© 2000, Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, CA 94112.
by Jodi Asbell-Clarke and Jeff Lockwood
(or Whom) Are We Looking For?
Where Do We Look?
Lessons from Our Past
The Search Is On
What Does the Public Have to Learn from All This?
A High School Curriculum in Astrobiology
Illustration courtesy of and © 2000 by Kathleen L. Blakeslee.
Astrobiology seems to be all the buzz these days. It was the focus of the ASP science symposium this summer; the University of Washington is offering it as a new Ph.D. program, and TERC (Technical Education Research Center) is developing a high school integrated science course based on it. So what is astrobiology?
The NASA Astrobiology Institute defines this new discipline as the study of the origin, evolution, distribution, and destiny of life in the Universe. What this means for scientists is finding the means to blend research fields such as microbiology, geoscience, and astrophysics to collectively answer the largest looming questions of humankind. What it means for educators is an engaging and exciting discipline that is ripe for an integrated approach to science education. Virtually every topic that one deals with in high school science is embedded in astrobiology.
What (or Whom) Are We Looking For?
Movies and television shows such as Contact and Star Trek have teased viewers with the idea of life on other planets and even in other galaxies. These fictional accounts almost always deal with intelligent beings that have evolved to a point of being able to communicate with humans. This is very appealing and makes for a great storyline, but in reality, it is much more likely that the Universe may be teeming with life on a much more basic level. Even on Earth, an overwhelming majority of the biomass with which we share our planet is in the form of microorganisms. So the first thing we have to do is understand what we mean by "life on other worlds" and figure out how to search for it.
Earth is the only known case study, and we must take from it any lessons we can. Apparently, as soon as Earth was mature enough for life to form here, it did. We have evidence of microbial life dating back 3.9 billion years, over 80 percent of the entire lifetime of the planet. This is helpful since it means that someone searching for life on Earth would have had a long timeframe within which to find it. Searching for microbial life elsewhere may not be as easy as finding an alien knocking on our back door, but it certainly seems a more likely prospect.
Because we are not going to be able to observe microbes, or even human-sized creatures, on other planets, we have to look for secondary evidence of life, called "biomarkers." These include the trace gases and elements given off as byproducts of microbial life. For example, oxygen, detected in a planetary atmosphere or in an auroral discharge, would be indicative of plant life. Detecting methane or sulfur compounds might indicate energy processes of microbial life such as bacteria. By using spectroscopy and other remote sensing devices, we can search for these elements on bodies in our Solar System and perhaps in the future we will be able to detect these elements on the planets being discovered around other stars.
Where Do We Look?
Deep ocean vents are essentially geysers on the ocean floor and are associated with areas of active seafloor spreading. Spewing hot, mineral-rich material into the frigid, surrounding water, such vents are known to harbor bacterial life. Photo courtesy of the University of Delaware College of Marine Studies.
One may be tempted to rule out various places in our Solar System as sites that harbor life because of their extreme conditions. Planets too far from the Sun seem far too cold and dark to host life, right? Not necessarily. We only have to look as far as our own terrestrial backyard to find contradictions to this intuition about life.
Extremophiles are creatures living at what are considered extreme conditions with respect to human life. Different life forms have been found on Earth at temperatures greater than waters boiling point and below its freezing point, in high acid and base conditions, at 4 km below the land surface and at 6 km below sea level. Microbes have lived in space for years, unprotected from extreme radiation.
A crucial example of life under extreme conditions resides in deep-sea vents first discovered in 1977. At depths of 2,100 meters on the floors of the Atlantic and Pacific Oceans, these chimney-like vents spew water heated by a geothermal energy source along with minerals that help support life forms such as tubeworms, clams, and shrimp. The water temperature reaches 750° F but does not boil because it is under tremendous pressure on the ocean floor.
At the other extreme, Lake Vostok sits 4,000 meters under the ice about 1,000 km from the South Pole. This lake provides an Earth-based laboratory that may provide great insight into what is occurring elsewhere in the Solar System. It is thought to have conditions similar to one of Jupiters moons, Europa. Lake Vostok is a unique and precious resource, and scientists must collect samples and pursue investigations without contaminating it. The introduction of any kind of evolved life form into Lake Vostok could perturb this ecosystem so that it no longer serves a purpose for astrobiology.
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