《Humanity 》作者：- Jerry Oltion 【EPUB】

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ISAAC ASIMOV’S ROBOT CITY ?? ROBOTS AND ALIENS ?? Book 6 ?? Humanity by Jerry Oltion ?? Copyright ?? 1990 ?? ?? ROBOTS AND EVOLUTION BY ISAAC ASIMOV ?? In general there are two types of change that take place in the Universe: catastrophic andevolutionary. A catastrophic change is characterized by a large alteration of conditions in a short period oftime. An evolutionary change is characterized by slow alterations of conditions over a longperiod of time. Clearly catastrophic change is more dramatic but if we observe the Universe around us it isequally clear that evolutionary change is the rule. A star shines for anywhere from many millions to many billions of years slowly evolving untilit reaches a point where if it is large enough there is an overbalancing so to speak andin the space of a few minutes or a few hours it explodes as a supernova and collapses.Catastrophe But thereafter it exists as a white dwarf neutron star or black hole andreturns to prolonged evolutionary change. Again a huge cloud of dust and gas slowly circling and condensing undergoes evolutionarychange until its center reaches the level of temperature and pressure where nuclear fusion canbegin. There is then ignition and a sun is born. Catastrophe But thereafter a planetarysystem evolves over the space of a few million years achieves equilibrium and continues toevolve over the space of a few billion years. Still again a planet like Earth can evolve geologically over a period of millions of yearsperhaps even billions undergoing slow changes that result in sea-floor spreading movingplates and shifting continents rising and eroding of mountain chains and so on. There arepunctuations in the form of minor catastrophes an earthquake here a volcanic eruption therea sudden flooding yon but beyond and between such events