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14 How Aliens Work 14 How Aliens Work How Aliens Work How Aliens Work and evolved on Earth, what governs the way life following points to it: is organized and what makes a planet habitable. Similar organisms reproduce similar Astrobiology combines the disciplines organisms -- a dog reproduces a dog, a of biology, chemistry, physics, geology and dandelion reproduces dandelions and a fish astronomy. Often, astrobiologists must use the reproduces a fish. information learned about life on Earth as a O ften, the number of offspring are guide for studying life elsewhere. Let's examine overproduced such that the number that survive some of the things that we have learned from is fewer than the number reproduced. life on Earth. In any population, individuals vary with respect to any given trait, such as height, skin What is Life? color, fur color or shape of beaks, and these variations can be passed on to the next While it is hard to pen a clear definition of generation. "life," most biologists agree that there are many Some variations are favorable, in that characteristics in common among living things. they make those individuals best-suited to their If an object meets these characteristics, it is environment, and some are not. Those considered alive: organisms with favorable variations will survive Organized - Living things are made of and pass those traits on to their offspring; those by Craig Freudenrich, Ph.D. atoms and molecules that are organized into individuals with unfavorable variations will die by Craig Freudenrich, Ph.D. and not pass on their traits -- this is natural cells. The cells in an organism can be either uniform or specialized for various functions. selection. Are there other forms of life in the The cells can be further organized into tissues, Given sufficient time, natural selection universe? The scientific search for organs and systems. Living things on Earth are will accumulate these favorable traits. The extraterrestrial life forms has been bolstered by quite diverse as to their organization and species will evolve. two recent discoveries. First, the discovery of complexity. Although Darwin's theory of evolution life forms in exotic environments on Earth Homeostatic - Living things carry out was proposed to explain changes in Earth-based indicates that life is very hearty and can adapt to functions that keep them in a constant, species, its principles are general enough that it the strangest and most hostile environments. relatively unchanging state called homeostasis. could be applied elsewhere in the universe as Second, astronomers found planets orbiting For example, your body has systems that keep well. stars besides our sun -- over 50 extrasolar your body temperature constant -- you shiver if planets have been discovered as of 2001. Are you're cold, sweat if you're hot. Life in the Extreme there alien life forms on any of these planets? Reproduces - Living things make If alien life does exist, what might it be copies of themselves, either exact copies Up until about 30 years ago, it was like? Would it be simple forms of life such as (clones) by asexual reproduction or similar believed that all life on Earth was dependent bacteria, viruses or algae, or more advanced, copies by sexual reproduction. upon energy from the sun. Furthermore, it was multi-cellular creatures, perhaps even Grows/develops - Living things grow thought that you would probably not find life intelligent beings? Would aliens be animals, and develop from smaller and/or simpler forms. where temperatures were extremely hot, like in plants or have characteristics of both? Would For example, a human begins life as a fertilized geysers or hot springs, or extremely cold, like in they have arms and legs and walk upright as we egg, developing into an embryo, fetus and then the Antarctic desert. do? Would they depend upon vision as their a baby. The baby subsequently grows into a These ideas changed when primary sense or use another way to gather toddler, adolescent and adult. oceanographers explored hydrothermal vents, information about their surroundings? Would Takes in energy from the environment openings in the ocean floor where extremely they "breathe" oxygen or some other gas? - Staying in a relatively constant, organized hot, mineral-rich water erupts from the crust. Speculation about aliens has typically state violates the second law of Hydrothermal vents are located several miles been left to science-fiction authors, science- thermodynamics, which states that the degree of below the surface, on the ocean floor, where the fiction readers and Hollywood writers and disorder (entropy) of all objects increases. For a surrounding water is at or near freezing, it is directors. In this article, we will examine living organism to maintain organization, it absolutely dark and the pressure is high. In astrobiology, the scientific search for must take in, process and expend energy. The organized communities around the bases of extraterrestrial life. We'll apply what we have way humans and other animals do this is by these vents, called black smokers, scientists learned about life on Earth to speculate about eating food and extracting energy from it. found clams, crabs and exotic, giant tubeworms what alien life forms might be like. Responds to stimuli - Living things measuring 6 feet (2 meters) long. The water respond to changes in their environment. For coming out of these vents is 230 to 662 degrees example, if a stimulus causes you pain, you Fahrenheit (110 to 350 degrees Celsius). Greetings, Carbon-based Bipeds! respond by moving away from that object. If you place a plant near a well-lit window, the Continued on Page 15 Most of us picture alien life the way it's branches or shoots grow toward the light portrayed in movies, where aliens are (phototropism). For protection, some animals commonly depicted as human-like forms change color to blend in with their surroundings because they use actors either to play the roles (camouflage). directly in make-up or to be models for Adapted to its environment - The computer-generated animation. Also, audiences characteristics of a living thing tend to be suited relate to human-like aliens better than to more for its environment. For example, the fins of a exotic, monster-like creatures. However, the dolphin are flat and adapted for swimming. The human body plan -- bilateral symmetry with wing of a bat has the same basic structure as the one head, two legs and two arms -- stems from bones in a dolphin's fin, but has a thin when early amphibians and reptiles colonized membrane that enables flight. the Earth's land masses, and it seems unlikely that such a shape would evolve on an alien Now that we've got a definition of what world. So, let's forget Hollywood for the life is, we need to look at how it changes over moment and look closely at the real science of vast expanses of time. The basic rules governing astrobiology. whether species arise, live, remain unchanged Astrobiology is the scientific study of or become extinct are those of evolution by life in the universe. Astrobiologists seek to natural selection as proposed by Charles understand (among other things) how life arose Darwin. Darwin's theory of evolution has the