【正文】 ually bad news. An anism often can not survive with a mutated gene. And so a gene usually can not be passed on, unless it?s an exact copy. For memes however, fidelity is not always so important. For example, if you tell someone the alligator story I told you today, it probably won?t be word for word exactly as I said it. Still, it will be basically the same story, and the person who hears the story will be able to pass it along. Other memes are replicated with higher fidelity though, like the twinkle, twinkle song. It had the exact same words 20 years ago as it does now. Well, that?s because we see songs as something that has to be performed accurately each time. If you change a word, the others will usually bring you in line. They?ll say, ?that?s not how you sing it?, right? So, you can see how looking at pieces of cultural information as replicators, as memes, and analyzing them in terms of longevity, fecundity and fidelity, we can gain some inside about how they spread, persist or change Lecture 2 Astronomy Narrator Listen to part of a lecture in an Astronomy Class Professor: Last week, we covered some arguments against going back to the Moon. But there are pelling reasons in favor of another Moon landing too, um… not the least of which is trying to pinpoint the moon?s age. We could do this in theory by studying an enormous impact crater, known as the South PoleAitken Basin. Um…it?s located in the moon?s South Polar Region. But, since it?s on the far side of the moon, it can only be seen from space. Here is an image of…we?ll call it the SPA Basin. This colorcoated image of the SPA Basin, those aren?t its actual colors obviously, this image is from the mid 90s, from the American spacecraft called Clementine. Um… unlike earlier lunar missions, Clementine didn?t orbit only around the moon?s equator. Its orbits enable it to send back data to create this topographical map of … well, the grey and white area towards the bottom is the South Pole, the purples and blues in the middle correspond to low elevations the SPA Basin itself, the oranges and reds around it are higher elevations. The basin measures an amazing 2,500 km in diameter, and its average depth is 12 km. That makes it the biggest known crater in our solar system and it may well be the oldest. You know plaary researchers love studying deep craters until learn about the impacts that created them, how they redistributed pieces of a pla?s crust and in this case, we especially want to know if any of the mantle, the layer beneath the crust, was exposed by the impact. Not everyone agrees, but some experts are convinced that whatever created the SPA Basin did perate the Moon?s mantle. And we need to find out, because much more than the crust, the mantle contains information about a pla?s or Moon?s total position. And that?s key to understanding pla formation. Um… Dian? Dian: So, the only way to know the basin?s age is to study its rocks directly? Professor: well, from radio survey data, we know that the basin contains lots of smaller craters. So it must be really old, about 4 billion years, give or take a few hundred million years. But that?s not very precise. If we had rock samples to study, we?d know whether the small craters were formed by impacts during the final stages of plaary formation, or if they resulted from later meteor showers. Dian: But if we know around how old the Basin is, I?m not sure that?s reason enough to go to the Moon again. Professor: No…, but such crude estimates…um…we can do better than that. Besides, there are other things worth investigating, like is there water ice on the moon? Clementine?s data indicated that the wall of the southpolar crater was more reflective than expected. So some experts think there?s probably ice there. Also, data from a later mission indicates significant concentrations of hydrogen and by inference water less than a meter underground at both poles. Student: Well if there?s water, how did it get there? Underground rivers? Professor: We think meteors that crashed into the moon or tails of passing ets may have introduced water molecules. Any water molecules that found their way to the floors of craters near the moon?s poles, that water would be perpetually frozen, because the floors of those craters are always in shadow. Um…furthermore, if the water ice was mixed in with rock and dust, it would be protected from evaporation. Dian: So are you saying there might be primitive life on the moon? Professor: that?s not my point at all. Um… ., say there is water ice on the moon. That would be a very practical value for a future moon base for astronauts. Water ice could be melted and purified for drinking. It could also be broken down into its ponent parts oxygen and hydrogen. Oxygen could be used to breathe, and hydrogen could be turned into fuel, rocket fuel. So water ice could enable the cr