Source: Origins, A NOVA Presentation: "Where are the Aliens?"
Earth provides a comfortable and temperate environment for a wide variety of living organisms. However, in the past few decades, scientists have discovered unusual life forms thriving in areas where the majority of living things on Earth could never survive, such as by deep sea vents or in dry deserts. This video segment, adapted from NOVA, explores extreme forms of life on Earth, the importance of liquid water, and the possibilities of life elsewhere in the solar system.
Since the 1970s, a number of unusual organisms have been discovered in environments that are hostile to other living things. These organisms, called extremophiles because of their ability to survive at the extremes of typically hospitable conditions, thrive where other life would perish. For example, microbial life has been found deep underground in tiny spaces within rocks, in the frozen environment of Antarctica, in the searing hot waters of deep sea vents and hot springs, and in the harsh environments of dry deserts. Life has also been found in extreme conditions of high radiation, pressure, acidity, alkalinity, or salinity. With the discovery of such organisms, some scientists have broadened their definition of what a habitable environment might be to include a greater range of potential environments for extraterrestrial life.
All life has three main requirements for existence: elements, a source of energy, and a medium that allows for chemical reactions to occur. The first two requirements are readily available throughout the universe. The third requirement causes more controversy. On Earth, liquid water is that essential medium, but is it the only solvent that could sustain life?
Liquid ammonia could possibly fulfill the role of water. In our solar system, liquid ammonia is common, and it is similar to water as a solvent. However, it would be difficult for life to survive in an ammonia environment because the temperature range in which it exists as a liquid, -78°C to -33°C (-108°F to -27°F), is very small and extremely cold. At such low temperatures, chemical reactions happen incredibly slowly, which makes it unlikely that life could arise. Based on our experience on Earth, water appears to be a crucial ingredient for life.
Nevertheless, The National Academy of Sciences has organized a group of scientists to address the limits of organic life of planetary systems. Rather than restrict the search for life to carbon and water-based organisms, the committee is evaluating the possibilities for "weird life." When stretched outside the rules of standard biology, the search for extraterrestrial life opens up even more.
Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
We assign reference terms to each statement within a standards document and to each media resource, and correlations are based upon matches of these terms for a given grade band. If a particular standards document of interest to you is not displayed yet, it most likely has not yet been processed by ASN or by Teachers' Domain. We will be adding social studies and arts correlations over the coming year, and also will be increasing the specificity of alignment.