16.6 Key Terms
Acidophiles: the most acid-tolerant organisms that are capable of living at pH values near zero—about ten million times more acidic than human blood. 16.3
Alkaliphiles: organisms that can grow at pH levels of about 13, which is comparable to the pH of household bleach and almost a million times more alkaline than human blood. 16.3
Amino acids: organic compounds that are the molecular building blocks of proteins. 16.3
Astrobiology: the multidisciplinary study of life in the universe: its origin, evolution, distribution, and fate; similar terms are exobiology and bioastronomy. 16.3
Biomarker: evidence of the presence of life, especially a global indication of life on a planet that could be detected remotely (such as an unusual atmospheric composition). 16.4
Continuously habitable zone: defined by the range of orbits that would remain within the habitable zone during the entire lifetime of the star system. 16.4
Copernican principle: the idea that there is nothing special about our place in the universe. 16.2
Deinococcus radiodurans: an organism that can tolerate ionizing radiation (such as that released by radioactive elements) a thousand times more intense than humans would be able to withstand. 16.3
DNA (deoxyribonucleic acid): a molecule that stores information about how to replicate a cell and its chemical and structural components. 16.3
Drake equation: a formula for estimating the number of intelligent, technological civilizations in our Galaxy, first suggested by Frank Drake. 16.5
Extremophile: an organism (usually a microbe) that tolerates or even thrives under conditions that most of the life around us would consider hostile, such as very high or low temperature or acidity. 16.3
Fermi paradox: question asked by physicist Enrico Fermi based on teh Copernican principle’s suggestion that intelligent life like us might be common: “Where are they? If life and intelligence are common and have such tremendous capacity for growth, why is there not a network of galactic civilizations whose presence extends even into a “latecomer” planetary system like ours?” 16.2
Gene: the basic functional unit that carries the genetic (hereditary) material contained in a cell. 16.3
Habitable environment: an environment capable of hosting life. 16.3
Habitable zone: a region around a star where suitable conditions might exist for life. 16.4
Organic compound: a compound containing carbon, especially a complex carbon compound; not necessarily produced by life. 16.3
Organic molecule: a combination of carbon and other atoms—primarily hydrogen, oxygen, nitrogen, phosphorus, and sulfur—some of which serve as the basis for our biochemistry. 16.2
Oxidizing chemistry: a chemistry where molecules tend to accept electrons readily. 16.4
Photosynthesis: a complex sequence of chemical reactions through which some living things can use sunlight to manufacture products that store energy (such as carbohydrates), releasing oxygen as one by-product. 16.3
Protein: a key biological molecule that provides the structure and function of the body’s tissues and organs, and essentially carries out the chemical work of the cell.
Psychrophiles: cold-adapted cells. 16.3
Reducing chemistry: a chemistry where molecules tend to give up electrons readily. 16.4
RNA (ribonucleic acid): a molecule that aids in the flow of genetic information from DNA to proteins. 16.3
SETI: the search for extraterrestrial intelligence; usually applied to searches for radio signals from other civilizations. 16.5
Stromatolites: solid, layered rock formations that are thought to be the fossils of oxygen-producing photosynthetic bacteria in rocks that are 3.5 billion years old. 16.3
Thermophile: an organism that can tolerate high temperatures. 16.3
Tholins: complex organic compounds formed when the Sun’s ultraviolet light breaks apart and recombines the nitrogen and methane present in the Titan’s upper atmosphere. 16.4
