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Aliens Are there other forms of

游客2024-05-11  0
问题                                             Aliens
    Are there other forms of life in the universe’? The scientific search for extraterrestrial (ET) life forms has been bolstered by two recent discoveries. First, the discovery of life forms in exotic environments on Earth indicates that life is very hearty and can adapt to the strangest and most hostile environments. Second, astronomers found planets orbiting stars besides our sun—over 50 extrasolar planets have been discovered as of 2001. Are there alien life forms on any of these planets?
    If alien life does exist, what might it be like? Would it be simple forms of life such as bacteria, viruses or algae, or more advanced, multi-cellular creatures, perhaps even intelligent beings? Would aliens be animals, plants or have characteristics of both? Would they have arms and legs and walk upright as we do? Would they depend upon vision as their primary sense or use another way to gather information about their surroundings? Would they "breathe" oxygen or some other gas?
Greetings, Carbon-based Bipeds(两足动物)!
     Most of us picture alien life the way it’s portrayed in movies, where aliens are commonly depicted as human-like forms because they use actors either to play the roles directly in make up or to be models for computer-generated animation. Also, audiences relate to human-like aliens better than to more exotic, monster like. However, the human body plan bilateral symmetry with one
head, two legs and two arms—stems from when early animals such as lizard, crocodile, or dinosaur colonized the Earth’s land masses, and it seems unlikely that such a shape would evolve on an alien world. So, let’s forget Hollywood for the moment and look closely at the real science of astrobiology.
    Astrobiology is the scientific study of life in the universe. Astrobiologists seek to understand (among other things) how life arose and evolved on Earth, what governs the way life is organized and what makes a planet habitable.
    Astrobiology combines the disciplines of biology, chemistry, physics, geology and astronomy. Often, astrobiologists must use the information learned about life on Earth as a guide for studying life elsewhere. Let’s examine some of the unusual things that we have learned from life on Earth:
Life in the Extreme
    Up until about 30 years ago, it was believed that all life on Earth was dependent upon energy from the sun. Furthermore, it was thought that you would probably not find life where temperatures were extremely hot, like in geysers or hot springs, or extremely cold,’ like in the Antarctic desert.
    These ideas changed when oceanographers explored hydrothermal vents, openings in the ocean floor  where extremely hot, mineral-rich water erupts from the crust. Hydrothermal vents are located several miles below the surface, on the ocean floor, where the surrounding water is at or near freezing, it is absolutely dark and the pressure is high. In organized communities around the bases of these vents, called black smokers, scientists found clams, crabs and exotic, giant tubeworms measuring 6 feet (2 meters) long. The water coming out of these vents is 230 to 662 degrees Fahrenheit (110 to 350 degrees Celsius).
    How can these animals survive so far from the sunlight, under these extreme conditions? In the water, scientists found species of bacteria that split hydrogen sulfide(硫化物)from the water to get energy to make organic compounds. The tubeworms have bacteria in their tissues that help them derive energy from the water. The clams feed on the bacteria, and the crabs feed on the tubeworms.
    The discovery of hydrothermal-vent communities showed that it is possible for life to evolve in places without light from the sun, and in other worlds without sufficient light from the parent star. In view of the discovery of hydrothermal vents, it may be possible that life exists on Europa, an icy moon of Jupiter, which scientists believe has a water ocean beneath its icy crust.
    Life has been found in other extreme environments as well. Scientists discovered microcolonies of lichens(地衣) called cryptoendoliths in rock samples of the Antarctic desert, where temperatures  often drop to 100 degrees below zero and there is little or no liquid water. In contrast, thermophilic (heat-loving) bacteria have been found in hot springs where temperatures exceed the boiling point of water.
    If life can evolve in extreme environments on Earth, it seems possible that life may exist in the extreme environments of other worlds such as mars.
Speculation: What Might Aliens be Like?
    Since no extraterrestrial life forms have been conclusively discovered, alien physiology lies in the realm of our imagination. Science-fiction authors, especially the "hard" ones who try to adhere strictly to real science, have been doing this for years. They first design or build a world, carefully working out its physical, astronomical and ecological characteristics. Next, they work out what type of aliens could exist in that world. An example of one such world-building exercise can be found at the Epona Project, where several science-fiction writers came together to create a world called Epona, complete with planetary, geological and ecological data. One artist, Steven Hanly, created Epona creatures.
    For his novel "Mission of Gravity," Hal Clement created a world called Mesklin that circles a double star. Mesklin rotates once every eighteen minutes and has a flattened shape caused by its rotation. The gravity of Mesklin ranges from three times Earth’s gravity, at the equator, to seven hundred times at the poles. Mesklin has a hydrogen atmosphere and methane(甲烷) oceans. Mesklinites, one of the planet’s life forms, are small, centipede-like creatures made of an insect skeletal protein called chitin. They have 18 pairs of legs that end in sucker-like feet, forward pinchers for grasping, a strong circulatory system and absorb hydrogen right through their shells. They are immensely strong—a result of living on a high-gravity world, yet they have a fear of being picked up because a fall from a small height could be fatal on such high gravity.
    Previously we’ve envisioned an alien world and alien life forms. In our world, the planet orbits a bright star. Only 10 percent of the world is covered with surface water, but throughout the land mass there are pockets of water that collect under the sands from the sparse rainfall. The enyironment is hot and arid and the sunshine is bright. The planet is massive and has gravity that is one-hundred times stronger than that of Earth. The atmosphere is an Earth-like air mixture of helium, oxygen and carbon dioxide.
    The two alien life forms that we envision for this world are animals—mobile predators that live around the planet’s few small bodies of surface water. Both aliens are short, about 1 foot (30 centimeters) tall, with thick limbs to support their weight against the immense gravity. Both have thick coverings or skins to minimize evaporation and conserve water. To gather information, one relies primarily on vision, while the other uses chemical senses (taste and smell).
    The Lashlarm is our first alien predator. It looks like a walking toilet bowl. The mouth portion is supported by three stalky legs connected to a flat base. Underneath the base are many scales, so the base glides across the surface of the sand much like a snake moves along the ground. It has several sensory appendages that allow it to locate prey by chemical means. It hunts near the small bodies of surface water, feeling along the water’s edge and tasting the sand and water for other animals. Upon locating prey, the Lashlarm crouches down and glides up to it. The Lashlarm then opens its large mouth and springs down upon the prey, swallowing it whole.
    The Nirba is slightly larger than the Lashlarm. It lives in the water, near the edge, much like a crocodile or alligator but is not fully aquatic(水栖的). The Nirba comes out to prey on other animals that come down to the water, particularly the Lashlarm. It has a large head with nostrils located on top of its nose so it can breathe while mostly submerged. The Nirba has thick skin, to prevent dehydration while out of the water in the hot sun, and big, muscular front legs with large claws for killing its prey. A long tail helps it swim in the water, and the "arrowhead" end assists in hunting and territorial defense.
选项 A、Y
B、N
C、NG
答案 B
解析 由题干关键词50 extrasolar planets可将答案定位至第一段第四句。该句的意思是，天文学家发现了很多围绕除太阳以外的恒星运转的行星，到2001年为止就发现了50多颗太阳系以外的行星。原文中的as of意为“到…为止”，而题干错误理解为在2001年发现了50多个行星。
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