This is an explanation for passage 1 of LSAT preptest 62, the December 2010 LSAT. This passage is about the use of lichenometry in studying earthquakes. The author discusses how lichenometry works and its advantages over radio-carbon dating.
This section has paragraph summaries and an analysis of the passage, links to the explanations for the questions are below.
Paragraph Summaries
- Radio-carbon dating is the traditional method of dating past earthquakes.
- Lichens grow at a constant rate, and they grow on rocks exposed by earthquakes. Geologists are now using lichens to date past earthquakes.
- Lichenometry is more accurate, but only for the past 500 years. Weather must be taken into account.
Analysis
This is a detail-heavy passage. It’s not an argument. Instead, it’s a scientific discussion of the advantages and disadvantages of lichenometry.
You shouldn’t try to memorize all the details on a passage like this, but you should know roughly where they are. For example, if a question asks about how lichenometry works, that’s the second paragraph. If it asks when to use lichenometry, that’s the third paragraph.
You should retain a few key points as well. The summaries I wrote above are what I remember from each paragraph. I know more than that of course, but I know the details I wrote especially well.
If you had trouble understanding this passage, then I recommend you go to the library, and get 20-30 back issues of the Economist. Then read their science section. Each issue has 2-3 pages of science.
The Economist’s science section is very well written. It doesn’t dumb down the science, but it’s written at a level that an intelligent non-scientist can understand. If you read many of these articles, you’ll develop a base of general scientific knowledge that will serve you well on all science passages.
Lichenometry is a new method that offers some advantages over radio-carbon dating
The gist of this passage is that when there’s an earthquake, rock is exposed. The largest amounts of rock are exposed at the center of the quake. When rock is exposed, lichen grows on it. And lichen grows at the same speed, for a very long time.
So you can identify when and where an earthquake happened by studying lichen. It’s generally quite accurate, though there are a few factors that affect lichen growth (lines 54-58), so these must be accounted for.
Radio-carbon dating is the traditional approach, but the third paragraph explains that it can be inaccurate in some circumstances. I didn’t memorize the specifics, I just made sure I knew where they are in case a question asks about them.
Note that lichenometry is new. It has some advantages, but the passage is not saying that we should get rid of radiocarbon dating and only use lichenometry. We have know idea if many scientists use lichenometry. Perhaps only its inventors, Bull and Brandon, use it.
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