【正文】 aps one in 100,000 stars might have a lifebearing planet orbiting it. That means that our nearest neighbours are perhaps 100 light years away, which is almost next door in astronomical terms.DAn alien civilization could choose many different ways of sending information across the galaxy, but many of these either require too much energy, or else are severely attenuated while traversing the vast distances across the galaxy. It turns out that, for a given amount of transmitted power, radio waves in the frequency range 1000 to 3000 MHz travel the greatest distance, and so all searches to date have concentrated on looking for radio waves in this frequency range. So far there have been a number of searches by various groups around the world, including Australian searches using the radio telescope at Parkes, New South Wales. Until now there have not been any detections from the few hundred stars which have been searched. The scale of the searches has been increased dramatically since 1992, when the US Congress voted NASA $10 million per year for ten years to conduct a thorough search for extraterrestrial life. Much of the money in this project is being spent on developing the special hardware needed to search many frequencies at once. The project has two parts. One part is a targeted search using the world’s largest radio telescopes, the Americanoperated telescope in Arecibo, Puerto Rico and the French telescope in Nancy in France. This part of the project is searching the nearest 1000 likely stars with high sensitivity for signals in the frequency range 1000 to 3000 MHz. The other part of the project is an undirected search which is monitoring all of space with a lower sensitivity, using the smaller antennas of NASA’s Deep Space Network.EThere is considerable debate over how we should react if we detect a signal from an alien civilization. Everybody agrees that we should not reply immediately. Quite apart form the impracticality of sending a reply over such large distances at short notice, it raises a host of ethical questions that would have to be addressed by the global munity before any reply could be sent. Would the human race face the culture shock if faced with a superior and much older civilisaiton? Luckily, there is not urgency about this. The stars being searched are hundreds of light years away, so it takes hundreds of years for their signal to reach us, and a further few hundred years for our reply to reach them. It’s not important, then, if there’s a delay of a few years, or decades, while the human race debates the question of whether to replay, and perhaps carefully drafts a reply.Reading Passage 3The history of the Tortoise Richard Dawkins ,The Guardian, Saturday 26 February 2005。In the second of three essays written on a recent visit to the Gal225。pagos Islands, Richard Dawkins considers another of the extraordinary creatures that helped inspire Darwin39。s theory of evolution.If you go back far enough everything lived in the sea: watery alma mater of all life. At various points in evolutionary history, enterprising individuals within many different animal groups moved out onto the land, sometimes even to the most parched deserts, taking their own private sea water with them in blood and cellular fluids. In addition to the reptiles, birds, mammals and insects which we see all around us, other groups that have succeeded out of water include scorpions, snails, crustaceans such as woodlice and land crabs, millipedes and centipedes, spiders and their kin and various worms. And we mustn39。t forget the plants, without whose prior invasion of the land none of the other migrations could have happened.Moving from water to land involved a major redesign of every aspect of life, from breathing to reproduction: it was a great trek through biological space. Nevertheless, with what seems almost like perversity, a good number of thoroughgoing land animals later turned around, abandoned their hardearned terrestrial retooling, and trooped back into the water again. Seals and sea lions (such as the breathtakingly tame Gal225。pagos sea lion) have only gone partway back. They show us what the intermediates might have been like, on the way to extreme cases such as whales and dugongs. Whales (including the small whales we call dolphins), and dugongs with their close cousins the manatees, ceased to be land creatures altogether and reverted to the full marine habits of their remote ancestors. They don39。t even e ashore to breed. They do, however, still breathe air, having never developed anything equivalent to the gills of their earlier marine incarnation. Turtles went back to the sea much longer ago and, like all vertebrate returnees to the water, they breathe air. However, they are, in one respect, less fully given back to the water than whales or dugongs, for turtles still lay their eggs on beaches. There is evidence that all modern turtles are descended from a terrestrial ancestor which lived before most of the dinosaurs. There are two key fossils called Proganochelys quenstedti and Palaeochersis talampayensis dating from early dinosaur times, which appear to be close to the ancestry of all modern turtles and tortoises. You might wonder how we tell whether fossil animals, live on land or in water, especially if only fragments are found. Sometimes it39。s obvious. Ichthyosaurs were reptilian contemporaries of the dinosaurs, with fins and streamlined bodies. The fossils look like dolphins and they surely lived like dolphins, in the water. With turtles it is a little less obvious. One way to tell is by measuring the bones of their forelimbs.Walter Joyce and Jacques Gauthier, at Yale University, took three measurements in these particular bones of 71 species of living turtles and tortoises. They used a kind of triangular graph paper to plot the three measurements against one another. All the land tortoise species formed a tight cluster of points in the upper part of the triangle。 all the water turtles clust